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Emma Stein
Introductory Life Sciences
APES Notes
BIOL(1000)
2018
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Animal Structure and Function – Prof Graham Alexander
The Circulatory System:
↳ Rapid transport system
Functions of the Circulatory System:
1. Nutrient and waste transport:
- Ingestion ➞ digestion ➞ absorption ➞ assimilation ➞ egestion ➞ excretion
2. Oxygen and carbon dioxide transport:
- Oxygen is used by the circulatory system for metabolism
- Carbon dioxide is therefore the byproduct
3. Thermoregulation (physiological):
- Regulation of body temperature is split into two categories:
↳ Physiological and behavioural
4. Hormone control:
- Hormones are transported from the place of manufacture to the location of use by the
circulatory system
5. Body defences:
- The lymphatic system
6. Structural function:
- This occurs in the organs of some organisms, such as roundworms
- It doesn’t apply to mammals as they have bones for structure
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Types of Circulatory Systems:
1. No circulatory system:
- i.e. bacterium / flatworms (Platyhelminthes)
- Cells in organisms without a circulatory system rely on diffusion in order to receive
oxygen
- These organisms need to have a large surface area in order for diffusion to take
place and for the oxygen to reach the cells
- The diffused oxygen doesn’t need to diffuse very far because the cells which
are receiving oxygen are relatively close to the surface
2. Unspecialised system:
- i.e. roundworms (coelom / pseudocoelom)
- These organisms are filled with fluid, and they contain muscle cells
- They are thus able to move different molecules around the body quite easily by
contracting the muscle cells
- They also use the fluid as a rudimentary system
- They are able to change their shape due to hydrostatic pressure
3. Specialised, open system:
- i.e. insects, mollusks, sea-squirts and hagfish (which are partially open)
- Vessels run through the bodies of these organisms – the heart contracts and increases
the pressure in those vessels
- The fluid in the heart moves down a pressure gradient
- The vessels are open-ended; meaning that they open into the interstitial space
➢Systems which contain valves are responsible for restricting the direction of the
movement of fluid – sea-squirts do not contain valves; therefore, the direction of
the blood is determined by the contractions of the heart
➢Insect blood does not contain haemoglobin, and they don’t use their circulatory
system to transport oxygen; therefore, they have many airways which direct
oxygen to their cells
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4. Specialised, closed, one cycle system:
- i.e. fish / annelids (leaches / earthworms)
- Some organisms, such as annelids, can contain more than one heart which pumps the
blood in one direction
- The blood moves into vessels which then branch off into capillaries
- The capillaries then join to form one big vessel again which further directs the
blood back to the heart
➢These organisms collect oxygen from the body surface via diffusion
- In fish, blood gets pumped out of the heart and it moves to the gills (which are finely
branched vessels)
- Blood and oxygen are then pumped to the different vessels, capillaries and organs
➢When the blood moves into the capillaries, the pressure decreases – there is
friction in vessels, and the surface area in capillaries is greater than that of the
vessels; therefore, there is an increase in friction in the capillaries
➢In organisms with a one-cycle system, the blood pressure is often lower than that of
organisms with a two-cycle system
In closed systems:
- The movement of blood in these organisms is controllable
- These organisms have a high blood pressure
- The pressure differential allows for ultra filtration
5. Specialised, closed, two cycle system:
- i.e. mammals / birds
➢These organisms have lungs instead of gills
- Blood gets pumped out of the heart and goes to the lungs
- The blood gets oxygenated in the lungs, goes back to the heart, and is then
pumped out of the heart again to be sent to different parts of the body
- The blood is pumped out of the heart at a very high pressure
- For every time blood is delivered to the tissues, it has already been to the heart
twice – that is why it is called a ‘two cycle system’
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Components of the Circulatory System:
1. Heart – muscular organ
2. Arterial system – delivers blood from the
heart either to the lungs or the body
3. Capillaries – finely divided vessels with a
large surface area that result in the delivery
of oxygen
4. Venous system – vessels that collect blood
from the capillary bed and deliver it back to
the heart
5. Lymphatic system – responsible for taking
fluids that move out of the circulatory
system and putting them back in the
circulatory system
Mammalian Circulation:
➢The circulatory system is composed of two circulatory paths:
- Systemic circulatory system – occurs between the heart and the rest of the body
- Circulation of blood in which oxygenated blood is pumped from the heart to the
body and deoxygenated blood is returned back to the heart
- Pulmonary circulatory system – occurs between the heart and lungs
- Circulation of blood in which deoxygenated blood is pumped from the heart to
the lungs and oxygenated blood is returned to back to the heart
➢The flow rate in these two systems is exactly the same
- Right ventricle pumps blood to lungs via pulmonary arteries ➞ blood flows through
capillary beds in the lungs, and loads O2 and unloads CO2 ➞ oxygenated blood returns
to left atrium via pulmonary veins ➞ this blood moves from left atrium to left ventricle ➞
left ventricle pumps this blood to body tissues via the aorta ➞ blood moves from aorta
to capillary beds in head and arms, then abdomen, then legs ➞ capillaries rejoin to form
venules ➞ the deoxygenated blood now moves from venules to superior vena cava ➞
this blood returns back to right atrium, and then flows into the right ventricle
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The Heart:
- Most organisms have only one heart, but some may have more than one
- The heart is the primary pump of the circulatory system
- The ability of the heart to pump blood is based on its ability to contract
- The heart is essentially a muscle around a tube or chamber
- Two main types of hearts:
- Peristaltic hearts – generally limited to small organisms such as insects
- Chambered hearts – found mammals and birds
The Mammalian Heart:
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- The mammalian heart consists of four chambers: two atria and two ventricles
- Atrial walls are thinner than the ventricle walls
- Atria supply blood to ventricles, and ventricles supply blood to the rest of the body
➢The left ventricle is thicker than the right one; thus, it contracts with a greater
force than the right ventricle; however, the same volume of blood is pumped
during each contraction
- The ventricular septum separates ventricles
➢Once expelled from the venous system, blood doesn’t move back into the venous
system due to the presence of valves
- Valves work in relation to a pressure gradient
- Valves determine the direction of blood flow in the body
Systole and Diastole:
- During every cardiac cycle, the heart contracts and relaxes:
- Contracting = heart pumps out blood
- Relaxing = chambers of heart fill with blood
➢Contraction phase = systole, and relaxation phase = diastole
Phases of the Cardiac Cycle:
1.
Atrial and ventricular
diastole: all chambers
are relaxed, and blood
flows int the heart
2. Atrial systole and
ventricular diastole:
atria contract pushing
blood into the ventricles
3. Atrial diastole and
ventricular systole: after
atria relax, the ventricles
contract pushing blood
out of the heart
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Heart Attack (Myocardial Infarction):
- When blood exists the heart, several coronary arteries immediately branch off to supply
the heart muscle
- If one or more of these arteries are blocked, the heart muscle cells will quickly die,
and this is called a heart attack
Atherosclerosis:
- Chronic cardiovascular disease where blood vessels become impaired gradually
- Vessels are narrowed by plaques of cholesterol and other substances that form in
the inner walls of arteries
Hearts of a Hagfish:
Hagfish have three hearts which transport blood around the body. In most organisms,
usually blood only gets pumped out of the heart and not back in; however, hagfish hearts’
pump and suck blood – the hearts beat by moving blood from one side to another.
When the muscle contracts, the volume in the chamber on the right-hand side increases.
Then the T cartilage bends, pushing against the other chamber so blood leaves the heart.
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Arteries vs Veins:
- Blood pressure through arteries is very high
- Arteries have a thick sheath of connective tissue which gives the vessels resistance
to being damaged by the high pressure
- Inside the connective tissue is smooth muscle and a layer of endothelium,
which lines the inner surface of the vessel
- Veins have the same structure as arteries; however, veins also contain valves, whereas
arteries do not, due to the fact that the blood pressure in arteries is too high
➢The valves stop the back-flow of blood
➢The volume of blood in the venous system is greater than that of the arterial system
- The smooth muscle in veins is thinner than the smooth muscle in arteries
Capillaries:
- Capillaries do not contain smooth muscle
- Capillary beds rely on the arterial system
➢The biggest volume of blood per unit length is found in the capillary beds
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Reptilian Circulatory System:
In reptiles:
- The ventricular septum is incomplete
- There are two systemic arches
- Priorities are different from mammals
RA
LA
Body
Lungs
RV
LV
Turtle Thermoregulation:
- Turtles bask on surface of the water ➞ when conditions are calm, the protruding shell
becomes dry ➞ their lungs are below the highest point of their shell ➞ they undergo
intermittent breathing ➞ breath holding associated with contraction of pulmonary
sphincter ➞ the turtle then breathes and moves heat into body to regulate temperature
Turtle Circulatory System:
RA
LA
Lungs
Body
RV
LV
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Lymphatic System:
- Vessels in the lymphatic system are open ended
- It receives fluids that are forced across the capillary wall
- It contains one-way valves
- There are no pumps in mammals, but there are in other organisms
- Thicker vessels may be surrounded by smooth muscle, but movement is usually
achieved indirectly by skeletal muscles
- Thoracic ducts empty into the subclavian veins through a one-way valve
- The subclavian veins connect to the anterior vena cava to transport fluids into the
heart
- Movement of plasma and small molecules occurs down a pressure gradient
- The gaps that the small molecules move through are small, and thus function as a
sieve – larger molecules are too big to pass through
- There is an osmotic gradient that slows the movement of plasma (the blood plasma has
5x the concentration of proteins than the interstitial fluid)
- The osmotic gradient occurs in the opposite direction to the pressure gradient
How Does a Heart Beat?
Electrical Activity of the Heart:
1. Electrical activity is initiated in the pacemaker region of the heart and spreads from
there
2. Cells are electrically coupled via membrane junctions
3. Pacemaker cells are in the sinoatrial node are auto-rhythmic; meaning that the heart is
myogenic (originating in muscle tissue)
4. The cells with the fastest rhythm over-shadow the slower pacemaker cells – slower
cells are called ‘latent pacemakers’
5. A pulse consists of a rapid depolarisation and then slower repolarisation of the cells
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Heart Muscle Consists of Three Types of Fibres:
1. Muscle cells found in the sinoatrial node and the atrioventricular node:
- Small and only weakly contractile, and have very slow conduction between cells
- The cells in the sinoatrial node are auto-rhythmic (0.05 m.s-1)
2. Muscle cells in the ventricular endocardium:
- Also weakly contractile but have very fast conduction
- Large and constitute the system spreading the excitation over the heart (5.0 m.s-1)
3. The rest of the heart muscle cells make up the bulk of the heart:
- Intermediate in size and are strongly contractile
- They have a medium rate of spread (0.8 m.s-1)
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Transmission:
1. Sinoatrial node
2. Both atria in a concentric fashion (pushes blood from the atria to the ventricles)
3. Atrioventricular node
4. Junctional fibres
5. Nodal fibres
6. Bundles of His (left and right)
7. Purkinje fibres
8. Ventricles (pumps blood into the arterial system)
Human Foetal Heart:
- The intake of oxygen differs in foetuses and adults; adults receive oxygen from air,
whereas foetuses receive oxygen from their mother
- A foetus does not use its own lungs until birth; therefore, the foetal heart does not have
to pump blood to the lungs because the foetus receives oxygen from the placenta
➢The pulmonary artery and the aortic artery are connected by the ductus arteriosus
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Control of Blood Flow:
- Governed by demands of the animal
- Complex because there are many needs and functions that must be maintained
- Three main levels of control:
- Heart function (stroke volume and heart rate)
- Arterial blood flow
- Capillary blood flow
The Nervous System:
- The nervous system is split into two types: central nervous system (CNS), and
peripheral nervous system (PNS)
- CNS consists of the brain and spinal cord
- PNS consists of afferent and efferent nervous systems
- Afferent: receives signals from the body and sends them to the brain
- Efferent: takes messages from CNS to various points in the body
- The efferent nervous system is:
- Voluntary
- Neuro-endocrine
- Autonomic (sympathetic and parasympathetic)
Cardiovascular Control:
- Regulation of arterial pressure to maintain blood flow in capillaries
- Information from receptors is fed to the brain
- Integration in medulla oblongata where there is an accelerator and inhibitor centre
- Output is fed to autonomic motor neuron that innervates the heart
- Main effect is on the heart rate – tachycardia (increase in heart rate) and bradycardia
(decrease in heart rate)
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Nerves and Receptors:
- Baroreceptors: measures pressure in the arterial and venous systems, and is stimulated
by stretch
- Baroreceptors can essentially only stimulate high pressure
- Mechanoreceptors: found in the atrial and ventricular walls; it measures the force of
contraction and the degree of filling – it is stimulated by movement
- Chemoreceptors: measurement of the concentration of O2, CO2 and pH in the arterial
system – it is stimulated by low O2 and pH, and high CO2
- More CO2 in the blood leads to a lower pH
- Autonomic efferents:
- Parasympathetic nervous system slows down the heart by producing acetylcholine
at the sinoatrial node
- Sympathetic nervous system speeds up the heart by producing epinephrine
(adrenaline) at the sinoatrial node
Control of Arterial Blood Flow:
- It operates on a priority system – e.g. if the arterial pressure falls, blood flow to the gut,
liver and muscles is reduced to maintain blood flow to the brain and heart
- Arterioles are normally innervated by sympathetic nerves; but there are some exceptions
- These release norepinephrine from their endings, which bind to alpha receptors in
the vascular smooth muscle around the vessels
- This causes vasoconstriction, and thus a rise in blood pressure
- Vasodilation is stimulated by beta receptors
- Beta receptors are not innervated, but respond to changing levels of circulating
catecholamines
- Transmitters are released into the blood from the adrenal medulla
- An important constituent of these is epinephrine, which binds with the beta
receptors and causes vasodilation
- The release of epinephrine may still cause a rise in arterial blood
pressure because it also stimulates beta receptors in the heart; thus
causing an increase in cardiac output
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Summary of the Control of Arterial Blood Flow:
➢Vasoconstriction = narrowing of blood vessels
➢Vasodilation = widening of blood vessels
- Stimulation of sympathetic nerves causes peripheral vasoconstriction and a rise in
arterial blood pressure; whereas an increase in circulation of epinephrine causes a
decrease in peripheral resistance and a rise in arterial pressure
- Some arterioles are innervated by parasympathetic nerve circulation to the brain and
lungs
- These release acetylcholine when stimulated, and this causes vasodilation in these
vessels
- Response in any vascular bed depends on the type of catecholamine and the nature of
the receptors involved
Local Control at the Capillary Bed:
- The degree of dilation is dependent on local conditions of the tissues
- This ensures that the most active tissues have the most dilated vessels (the most
active tissues are supplied with the most blood)
- Active tissues produce CO2, H+ and other metabolites
- It is measured by chemoreceptors, and causes vasodilation and local
increases in blood flow
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Respiration:
- This is not metabolism; it refers to ‘breathing’
- The transfer of gases takes place in several stages:
1. Breathing movements ensure continuous supply of air / water to respiratory surface
2. Diffusion of O2 and CO2 across the respiratory epithelium
3. Bulk transport of gases by the blood
4. Diffusion of O2 and CO2 across capillary walls between blood and cells of tissues
Fick’s Law:
↳ M = rate of transfer
↳ D = diffusion co-efficient
↳ A = area
↳
= concentration gradient
↳ x = diffusion distance
Solution of Gases in Water:
- All respiratory epithelia must be kept moist; gases must be dissolved in water to be
taken up by the cells, and this can be a problem in terrestrial animals (especially in hot
and dry environments)
- Solubility of gases in water depend on several factors:
- Pressure / partial pressure of the gas
- Temperature (higher rates occur at higher temperatures)
- Solutes (solutes will decrease the solubility of gases)
- Solubility of the gas concerned (solubility can decrease with temperature)
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Counter Current Exchange:
100
90
100
10
80
70
80
30
60
50
60
50
40
30
55
55
20
10
55
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* Important Definitions:
- Diaphragm: muscular partition that separates the chest cavity from the abdominal
cavity, and plays a major role in breathing
- Trachea: the windpipe
- Bronchus: air passages beginning at the end of the trachea and branches into the lungs
- Bronchiole: tiny air tubes in the lungs that branch out from the bronchus
Air-sacs in Birds:
- The respiratory system in birds and mammals are very different
- Process of breathing in birds:
5. Bird breathes in, and air goes to posterior air sac; at the same time, air that was in
the lungs travel to anterior air sac
6. Bird breathes out, and air from anterior air sac leaves the body, and the air from the
posterior air sac goes into the lungs
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Advantage of Bird Respiratory System over Mammalian System:
- Mammals inhale, and then they exhale; however, when they exhale, there is still a very
small amount of air left in the lungs
- This is called ‘anatomical dead space’, and it occurs when they inhale, but the air
does not reach all places in the lungs
- With birds, there is no anatomical dead space because the air only flows in one
direction
➢The air sacs are the organs that are doing the pumping – muscle movement causes
compressions of the air sacs to suck and push out air respectively
Human Lungs:
- Surface area is 50-100 m2, and respiratory
epithelium is about 2 μm thick
- Ventilation is dependent on:
- Breathing rate
- Tidal volume
- Anatomical dead space (volume of the
non-respiratory trachea, bronchus and
bronchiole)
➢Mammals such as giraffes and elephants
probably have the largest anatomical dead space
* Important Definitions:
- Alveolar ventilation volume = tidal volume - anatomical dead space (avv = tv - ads)
- Total ventilation volume = alveolar ventilation volume x respiration frequency
- Anatomical dead space = 150 ml
- Residual volume = anatomical dead space + non-collapsing volume of deflated lung
(1.2 litres)
- Physiological dead space = air available for exchange but not functionally used
because of poor blood supply (150 ml)
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Breathing:
- At rest, breathing uses about 1-2% of total energy
- During exercise, breathing increases to 3-5%
- Energy goes into stretching the elastic connective tissue in the lungs and associated
muscles
- Most goes into overcoming the cohesive force of water molecules associated with
respiratory surface
- Septal cells of the alveolar epithelium produce a phospholipid mixture called the
pulmonary surfactant
➢Surfactant = a substance which tends to reduce the surface tension of a liquid in
which it is dissolved
- Intersperse between water molecules reduces cohesive forces so that the surface
tension of the water molecules, and thus the energy needed for ventilation, is reduced
- Air flow = pressure gradient / resistance
- Main factor affecting resistance is the diameter of the passageways
- Resistance is normally very low, and only 1-2 mm Hg is sufficient for effective
breathing
- Decrease in diameter or loss of surfactant can increase energy necessary for
breathing
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Control of Breathing:
- Control of the respiratory muscles can be very precise – allows for talking, whistling,
singing and breathing
- Intercostals and diaphragm are activated by the phrenic nerve and spinal motor neurons
- Mammalian respiratory centres are
found in the pons (pneumotaxic
centre) and the medulla
➢The pons is located above the
medulla oblongata in the brain
stem
- Inspiration centre and Expiration
centre make up the Central Rhythm
Generator
- Breathing can be controlled by
conscious violation
- Our voluntary nervous system
can override breathing; however,
most of the time breathing is
subconscious
Control of Breathing (Continued):
Breathing is mainly stimulated by CO2 (chemoreceptors) – the main effect of breathing
depends on the amount of CO2 in the body; not O2
Initiation of the inhalation phase
Expansion in the lung stimulates pulmonary stretch receptors
Termination of inhalation and the onset of exhalation
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Control of CO2 in the Lung:
CO2 levels in the alveoli increase
Relaxation of the bronchiolar smooth muscle
Bronchiodilation
More CO2 expired
Control of O2 in the Lung:
O2 levels in the alveoli decrease
Contraction of arteriolar smooth muscle
Vasoconstriction
Blood supply to the alveoli is reduced
Blood movement in arterioles is slowed
More time for O2 to diffuse
O2 Carrying Capacity:
- Volume of blood that has to be pumped is dependent on how much oxygen the blood
can carry
- If blood is more concentrated, less blood is needed to be pumped around the body
- There are adaptations for increasing oxygen carrying capacity of blood: haemoglobin
- In humans, 100 ml of blood can contain 20 ml of oxygen, and only about 0.5 ml of
oxygen is carried per 100 ml-1 in the plasma
➢The heart would have to pump 40x harder if we did not have haemoglobin
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The Exchange Process:
- O2 diffuses down the concentration gradient into the blood plasma
- It then diffuses into the red blood cells where it is bound by the haemoglobin
- This effectively removes the O2 from the solution so that the concentration of
free O2 in the plasma remains low
- This maintains the concentration gradient and allows as much as 40x the
amount of O2 to be carried by the blood
- Each haemoglobin molecule can carry four O2 molecules
- This molecule will then be considered 100% saturated
- Haemoglobin has a high affinity for O2 and it is due to this that it is so efficient at
mopping it out of the plasma
- If the O2 is so tightly bound to the haemoglobin, how is it given up where it is needed?
- The affinity of O2 and haemoglobin to each other is greatly affected by the pH and
CO2 concentration of the plasma
- At the cell site where oxygen is required, there is generally a higher concentration of CO2
- This causes the dissociation of the haemoglobin and O2
- This is known as the Bohr effect
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Dissociation Curve:
- At the lungs, where there is a high concentration of O2, the haemoglobin molecules will
be very saturated; but when there is a low concentration, the saturation of haemoglobin
is much lower
➢The Bohr Shift: additional O2 is released from haemoglobin when there is a lower pH
and higher CO2 concentration
➢The Bohr Effect means that haemoglobin will load more easily in the pulmonary
capillaries, and will unload more easily in the tissue capillaries
➢Low CO2 = high O2 affinity, and high CO2 = low O2 affinity
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- 20% of CO2 binds to haemoglobin
- Most CO2 is converted to bicarbonate and H+ in red blood cells by carbonate anhydrase
➢ CO2 + H2O ⇌ HCO3- + H+
➢Diffusion of O2 across the capillary wall into the alveolar happens when there is a
concentration gradient of CO2
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Metabolism:
➢This is the sum total of all chemical reactions in the body
- Two types of metabolism:
- Catabolism: break down of complex molecules into smaller, simpler molecules with
the release of energy / heat
- e.g. doing work
- Anabolism: construction of complex molecules with input of energy
- e.g. growth, healing (making things out of simple molecules)
Temperature and Metabolism:
- Temperature has a profound influence on organisms and their metabolic processes
- Active animal life ranges from about -2ºC to 50ºC body temperature (Tb), but most life is
generally between 3ºC and 40ºC
- Some animals can live in an inactive state outside of these temperatures
- Adaptation and tolerance of low temperatures is common, but adaptation to high
temperatures is rare
Temperature Classification of Animals:
- Most fundamental classification of animals is endotherm / ectotherm
- Endotherm: an animal that thermoregulates by balancing high rates of heat production
with high rates of heat loss
- i.e. they depend on internal generation of heat
- Ectotherm: an animal that thermoregulates by balancing heat gain and loss from the
environment
- i.e. they depend on external sources of body heat
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Relationship Between Environmental Temperature (Te) and Metabolism:
➞ There is a positive relationship
between temperature and metabolic
rate in ectotherms
➞ There is a negative relationship
between temperature and metabolic
rate in endotherms
- Thermal Conductance and Insulation: insulation is a consequence of conductance
- Metabolic Rate: endotherms have a higher metabolic rate than ectotherms
- Body Temperature (Tb): ectotherms have a lower body temperature than endotherms
Stability of Tb:
- Poikilotherm: variable Tb
- Tb is usually dependent on Te
- Homeotherm: Tb is constant and
independent of Te
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Heterothermy:
- Regional heterotherms are endothermic in parts of their bodies and ectothermic in
other parts – e.g. duck, tuna, marlin
- Temporal heterotherms are endothermic at one time and ectothermic at another – e.g.
naked mole rat, brooding python
Physiological Effects of Tb Change:
- Increase in body temperature usually increases rates of physiological processes
- Change in rates due to temperature are described by a coefficient called the Q10
- In general, a 10ºC change causes a rise in the rates of most processes 2 to 3 times
- If the rate doubles, the Q10 is 2; and if the rate trebles, the Q10 is 3
↳
Mechanism of Heat Death:
- Denaturation of proteins = thermal coagulation
- Thermal inactivation of enzymes
- Inadequate supply of oxygen
- Different temperature effects (Q10) on independent metabolic reactions
- Temperature effects on membrane structure
D
A
B
C
E
➢ The arrows above represent a Q10 coefficient
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Tolerance to Low Temperatures:
- The biggest problem with low Tb is danger of freezing
- When ice crystals form on the skin, the crystals penetrate the cell membrane, killing
the cells
- Some animals can tolerate freezing, but others die at much higher temperatures
- Two ways of dealing with freezing:
- Avoidance (depression of the freezing point; behaviour)
- Tolerance
- Those that cannot tolerate ice formation are called ‘freeze susceptible’
Freezing Avoidance: Antifreeze
- The body fluids of some cold-climate ectotherms contain antifreeze substances
- Some insects contain glycerol which increases in concentration during winter
➢Glycerol acts as an antifreeze
Freeze Tolerance:
- Few animals are freeze tolerant because:
- Freezing causes mechanical cell damage
- Freezing causes some organs to shut down before others
- Freeze tolerant animals prevent cell damage and organs are frozen in a sequence
- This is not such a problem with small animals
- In some species of beetles, extracellular fluids freeze in cold temperatures
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Freeze Tolerance (Continued):
1. Freezing of the intercellular water is induced
2. This increases the osmotic pressure in the intercellular spaces
- When the osmotic pressure increases, it causes a gradient, and due to this, the
concentration of the fluid in the intercellular spaces increases
3. Water is then drawn out of the cells
4. Intracellular osmotic concentration increases
5. This depresses the freezing point in the cell
Thermal Balance in Endotherms:
- Heat produced in the body must be transported to the surface before it can be lost;
therefore, the core must be warmer than the surface
- Organs in the chest and abdomen make up 6% mass, but produce 56% of heat at rest
- The brain can produce about 15% of heat
- Core and shell vary according to amount of heat produced and environmental
temperature, which affects heat loss rates
Mechanism of Tb Control:
- This happens at three levels:
1. Autonomic
2. Adaptive
3. Behavioural
- Control of hypothalamus: thermo-sensitive
and integrates input from afferents all over the
body
- Neurons in the hypothalamus increase in firing
rate above and below certain temperatures
- Range of Thyp between these levels is the ‘set
point range’ (Tset)
- This is referred to as the ‘dual threshold system’
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Variations in Tb in Endotherms:
- Tb is never entirely constant:
- In diurnal animals, Tb dips at night
- In nocturnal animals, Tb dips during the day
➢Human Tb varies by about 2ºC
- Torpor: many animals, especially small ones, allow Tb to drop much more on a daily
basis – an example of torpor is hibernation (on a seasonal basis)
Heat Production in Endotherms:
- Heat production cannot be turned down below a minimum level
- This is known as a ‘Basal Metabolic Rate’
- It can be turned up by:
- Muscular activity
- Shivering
- Non-shivering thermogenesis: metabolism of brown fat without noticeable
movement
➢Brown fat is found in young mammals, and it has high levels of mitochondria – this is
where the heat is produced
Heating and Cooling in Ectotherms:
- Ectothermic animals cannot modify their Tb by producing more heat
- But, they can modify rates of heat exchange with the environment
- When thermoregulating, they attempt to keep Tb near Tset
Cold
Hot
Tb
Te
Tb
Tset
Tb
Te
Tb
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Animal Structure and Function – Dr Darragh Woodford
Homeostasis:
Brief Outline of Human Organ Systems:
- Skeletal System: provides support and structure to the body, and protects internal
organs and soft tissues
- e.g. bones, tendons, ligaments, cartilage
- Muscular System: permits movement of the body, and provides support
- e.g. skeletal and smooth muscles
- Digestive System: breaks down food and absorbs its nutrients
- e.g. mouth, oesophagus, stomach, liver, pancreas, intestines, rectum, anus
- Respiratory System: takes in oxygen and releases waste gases
- e.g. nasal cavity, trachea, lungs
- Nervous System: network of cells and fibres that transmit nerve impulses between
different parts of the body – it controls sensation, thought, movement, and virtually all
other body activities
- e.g. brain, spinal cord, nerves, sensory organs
- Circulatory System: permits blood to circulate around the body and transport oxygen,
nutrients and other substances to cells, and carries away the waste
- e.g. heart, blood vessels, lungs
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- Lymphatic and Immune System: defence against infections
- e.g. bone marrow, lymph nodes, lymph vessels
- Excretory System: removal of metabolic waste, and controls osmotic balance
- e.g. kidneys, ureter, bladder, urethra
- Integumentary System: protection from mechanical injury and infections, protects
against dehydration, and is important for thermoregulation
- e.g. skin, hair, nails
- Endocrine System: chemical messenger system, and a regulatory system that coordinates body activities via hormone control
- e.g. pituitary gland, thyroid gland, adrenal gland, pancreas, testes, ovaries
- Reproductive System: reproduction
- e.g. testes, ovaries
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Exchange with the Environment:
➢ ICF = intracellular environment
➢ ECF = extracellular environment
Regulating the Internal Environment:
1. Mechanisms of Homeostasis Moderate Changes in the Internal Environment:
Claude Bernard (1859):
- External environment = surrounding the animal
- Internal environment = the place in which the cells of the animal actually live
- The internal environment of vertebrates is called the ‘interstitial fluid’
➢ Interstitial = between cells or tissues
- This fluid exchanges nutrients and waste with blood
➢The internal environment in vertebrates is constant even when the external environment
is changing
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Homeostasis:
- Homeostasis = ‘steady state’
- Homeo = same; stasis = staying
- e.g. the human body can maintain its internal environment at a constant
temperature of approximately 37ºC
- Dynamic equilibrium is maintained by negative feedback systems
- Regulators respond to counteract changes caused by stressors (such as a rapid
changes in external environment)
Three Models Resulting in Relative Homeostasis:
➞ Static equilibrium system in a
constant environment
➞ Open loop dynamic equilibrium
system
- When there is a change in the
external environment, the body
reacts to match that environment
➞ Closed feedback control loop
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2. Homeostasis Depending on Feedback Circuits:
- Any homeostatic control system has three functional components:
- The receptor detects a change in some variable in the animal’s internal
environment, such as a change in temperature
- The control centre processes the information it receives from the receptor and
directs an appropriate response by the effector
Negative Feedback:
Response loop
shuts off
Initial Stimulus
Response
Stimulus
- Change in the variable being monitored causes the control mechanism to counteract
further changes
- Owing to a time lag between receptor and response, the variable drifts slightly above
and below the set point
- There is constant overshooting and undershooting to ensure that the set point never
becomes too large or too small
Negative
Feedback
High
Homeostatic
Range
Negative
Feedback
Low
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➢ Body temperature is regulated / controlled by negative feedback
Positive Feedback:
Initial Stimulus
Response
Stimulus
Outside factor required
to shut off positive
feedback cycle
- Positive feedback involves a change in some variable that triggers mechanisms that
amplify change
- e.g. during childbirth, the pressure of the foetus’ head against sensors near the
opening of the uterus stimulates uterine contractions
- Positive feedback brings childbirth to completion; a very different sort of process
from maintaining a steady state
-
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Over the short term, homeostatic mechanisms can keep a process close to a set point
- e.g. body temperature
- Over the longer term, homeostasis allows regulated change in the body’s internal
environment
➢This is how bears are able to hibernate: they adjust their set points to slow down their
metabolism, which allows them to go for long periods of time without eating
- Internal regulation is expensive as energy is obtained from food
Physiological Systems of Animals Operate in a Fluid Environment:
- The relative concentrations of water and solutes in this environment must be maintained
within fairly narrow limits
- How? By balancing the uptake and loss of water, fluids and salts
Hypo-osmotic fresh water fish
Hyper-osmotic sea water fish
(hypertonic blood)
(hypotonic blood)
Osmoregulation:
- Osmoregulation is the active regulation of osmotic pressure of body fluids to maintain
homeostasis
- It regulates solute concentrations and balances the gain and loss of water in our
bodies
- All animals face the same central problem of osmoregulation
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Osmosis:
- Movement of water into and out of cells through a selectively permeable membrane
- Osmosis occurs whenever two solutions, separated by a membrane, differ in
osmotic pressure or osmolarity (moles of solute per litre of solution)
semi-permeable membrane
➢Water moves by osmosis into the solution of greater concentration until the volume
changes equalise the concentrations
➢The amount of pressure to counteract volume change is equal to the osmotic pressure of
the glucose solution
Diffusion vs Osmosis:
Diffusion:
Osmosis:
- Solvent and solute
particles move to
equalise
concentrations
- No semi-permeable
membrane is
involved
- Only solvent
Equalises
the concentration of two
solutions
particles move;
solute particles do
not move
- The movement is
through a semipermeable
membrane
➢An increase in osmotic pressure in a system will cause an increase in the diffusion of
water into the system
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Osmotic Challenges:
- Osmoconformers, such as marine animals, do not regulate their osmolarity
- Osmoregulators have to control water and salt levels in their bodies
Saltwater Fish:
- Most marine vertebrates are osmoregulators:
- Marine fishes constantly lose water through their skin and gills
- They obtain water in food and by drinking large amounts of seawater
- They excrete ions by active transport out of the gills
- Thus, they produce very little isotonic urine
Freshwater Fish:
- Freshwater fish are constantly gaining water by osmosis and losing salts by diffusion:
- They maintain water balance by excreting large amounts of very dilute (hypoosmotic) urine
- They regain lost salts in food
- Active uptake of salts from their surroundings
➢The body fluid of an osmoconformer would be iso-osmotic in a saltwater environment
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Freshwater Animals in Temporary Systems:
- Surviving periods of desiccation: anhydrobiosis
↳ an = without, hydro = water; and bioses = life
- Therefore, anhydrobiosis = life without water
- Resistant life stage (e.g. dormant, desiccated fairy shrimp eggs, or cysts)
- Adult cryptobiosis (e.g. tardigrades (water bears))
↳ crypto = hidden, and bioses = life
Land Animals:
- Land animals manage their water budgets:
- Drinking and eating moist foods
- Using metabolic water (water that can be stored in tissues in the body)
➢The threat of desiccation is perhaps the largest regulatory problem confronting terrestrial
animals – humans die if they lose about 12% of their body water
Terrestrial Environments:
Adaptations:
- Impermeable integument: humans do this to ensure that there is no passive water loss
though their skin
- Metabolic water
- Size: reduce the ratio between surface area and volume (the higher the surface area to
volume ratio, the easier it is to lose water)
- Specialised excretory organs: also to maintain salt balance
- Form in which nitrogen is excreted
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Nitrogenous Waste Reflecting Phylogeny and Habitat:
- During the breakdown of proteins and nucleic acids, enzymes remove nitrogen in the
form of ammonia (a small and toxic molecule)
- The type and quality of waste products has an impact on water balance
Nitrogenous Waste Products:
- Most aquatic animals (including most bony fishes) produce ammonia
➢Ammonia production = energy inefficient
- Mammals, most amphibians, sharks, and some bony fishes produce urea
➢Urea production = moderately energy efficient
- Reptiles, birds, insects and land snails produce uric acid
➢Uric acid production= energy inefficient, but water efficient
Water Balance Depends on Transport Epithelia:
- Transport epithelia move specific solutes in controlled amounts in particular directions
- They are arranged into complex tubular networks with extensive surface area
- e.g. the salt secreting glands of some marine birds secrete a fluid that is much
more salty than the sea
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Fluid Concentrations in Various Animals:
Fish:
- Blood concentration: hypo-osmotic with seawater
- Urine concentration: isotonic with blood
- Osmoregulation: aided by active ion secretion (gills)
Frog:
- Blood concentration: hyper-osmotic with freshwater
- Urine concentration: hypo-osmotic with blood (excretes ammonia as a tadpole, and
urea as a frog)
- Osmoregulation: aided by active ion absorption (skin)
Desert Mice:
- Urine concentration: hyper-osmotic with blood
- Osmoregulation: achieved through food and generation of metabolic water
Bird:
- Urine concentration: hyper-osmotic with blood (uric acid droppings)
- Osmoregulation: achieved by drinking fresh water; however, marine birds achieve this
by drinking sea water
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The Nervous System:
Forms of Communication to Maintain Homeostasis:
1. Neurons conduct signals quickly
2. Hormones conduct signals slowly
- Somatic = voluntary control of body movements (e.g. reflexes, blinking)
➢External and conscious
- Autonomic = control of bodily functions (e.g. regulation of body temperature, breathing)
➢Internal and unconscious
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General Arrangement of the Nervous System:
Neurons:
- Glial cells surround and support the neurons (glia = glue)
- Schwann cells form the lipid sheath called myelin
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Neurons Receive and Transmit Information:
- Dendrites receive signals and transmit them to the cell body
- Axons transmit signals to other neurons; e.g. a muscle, or a gland
- Synapses are junctions between neurons
Three Functional Types of Neurons:
Sensory Neurons
Efferent Neurons
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Nerve Signals:
1. Membrane Potential:
➢Every cell has voltage, or membrane potential across its plasma membrane:
- A membrane potential is a localised electrical gradient across a membrane
- Anions are more concentrated within a cell
- Cations are more concentrated in the extracellular fluid
Measuring membrane potentials:
➢An unstimulated cell usually has a resting potential of -70mV
How a cell maintains a membrane potential:
- Cations: K+ is the principle intracellular cation
Na+ is the principle extracellular cation
- Anions: Proteins, amino acids, sulphate and phosphate are principle intracellular anions
Cl- is the principle extracellular anion
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Equilibrium Situation:
IN (-VE)
OUT (+VE)
TYPE OF ION CHANNEL
[K+]
[K+]
Open at rest (not gateable)
x2
Pump
x3
[Na+]
[Na+]
Voltage dependent (gateable)
[A-]
None
None
[Cl-]
[Cl-]
Open at rest (not gateable)
Leakage
Movement across a cell membrane:
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Resting membrane potential is established due to:
- Very low permeability to Na+ ions
- Sodium-potassium ATPase pump ➞ pumps Na+ ions out as quickly as they move in
- The pump moves 3 Na+ ions out for every 2 K+ ions that come in
- Ungated ion channels allow ions to diffuse across the plasma membrane
- These channels are always open
➢Diffusion does not achieve equilibrium – ATPase pump transports ions against the
concentration gradient
2. Nerve Impulses:
➢Changes in the membrane potential of a neuron gives rise to nerve impulses:
- Excitable cells have the ability to generate large changes in their membrane
potentials
- Gated ion channels can open or close in response to stimuli
- Diffusion of these ions leads to a change in the membrane potential
Types of gated ion channels:
- Chemically-gated ion channels open or close in response to a chemical stimulus
- Voltage-gated ion channels open or close in response to a change in membrane
potential
Nerve impulses:
- Produced by changes in membrane permeability to ions
- Caused by the movement of ions
➢The more permeable the membrane is, the more ions it allows in
- This is referred to as the action potential
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Resting potentials:
1. Resting state:
- Voltage-activated Na+ and K+ channels are closed
2. Depolarisation:
- Voltage-activated Na+ channels open
- Na+ ions enter the cell, and the inside of the neuron becomes positive relative
to the outside
3. Repolarisation:
- Voltage-activated Na+ channels close
- K+ channels are open, and K+ moves out of the cell, restoring a negative charge
to the inside of the cell
4. Returning to resting state:
- Voltage-activated Na+ and K+ channels close
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Hyperpolarisation:
- Gated K+ channels open, and K+ diffuses out of the cell
- The membrane potential then becomes more negative
Depolarisation:
- Gated Na+ channels open, and Na+ diffuses into the cell
- The membrane potential then becomes less negative
The action potential:
- ‘All-or-nothing’ depolarisation
- i.e. either depolarisation happens or it does not
- If graded potentials sum to ≈ -55mV, a threshold potential is achieved
- This triggers the action potential, which takes place in the axons only
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Generation of action potentials:
1. Resting potential is established
2. Threshold potential is achieved (gates begin to open)
3. Depolarisation phase of the action potential occurs (Na+ gates open and Na+ moves in)
4. Repolarisation phase of the action potential occurs (K+ gates open and K+ moves out)
5. Undershoot occurs (Na+ gates close and K+ gates remain open)
- In the resting state, closed voltage-gated K+ channels open slowly in response to
depolarisation
- Voltage-gated Na+ channels have two gates
- Closed activation gates open rapidly in response to depolarisation
- Open inactivation gates close slowly in response to depolarisation
- During the undershoot, both the Na+ channel’s activation and inactivation gates are
closed
- At this time, the neuron cannot depolarise in response to another stimulus: this is
called the refractory period
➢It occurs when one of the action potentials is still finishing off, and thus another
one cannot be triggered until the first is finished
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Ion movement during the action potential:
Positive and negative feedback loops of action potentials:
Increase in membrane
conductance of sodium
Depolarisation
Increase in membrane
conductance of potassium
Depolarisation
Repolarisation
Na+ inflow
Positive Feedback
➢ g = membrane conductance
Negative Feedback
K+ outflow
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3. Propagation of Nerve Impulses:
➢Nerve impulses propagate themselves along an axon:
- The action potential is repeatedly regenerated along the length of the axon
- All-or-none action potentials are designed for long distance communication
- The refractory period makes impulse conduction unidirectional from the axon helix
to the end of the dendrite
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Recording the action potential:
- Movement of the action potential is called conduction
- Conduction is the flow of electrical energy from one part of the cell to another
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Propagation of a nerve impulse depends on:
- The electrical excitability of the axon membrane: the more gated ion channels the axon
membrane has, the quicker it can react to a change in the action potential
- Cable properties of the membrane
There are two types of conduction:
1. Continuous conduction:
- Takes place in unmyelinated neurons
- Involves the entire axon plasma membrane
2. Saltatory conduction:
- In myelinated neurons, only unmyelinated regions of the axon depolarises
- Thus, the impulse moves faster than in unmyelinated neurons
➢Blue arrows: in a myelinated axon, the depolarising current during an action potential
spreads along the interior of the axon
➢Red arrows: the action potential jumps from node to node as it travels along the axon
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4. Synapses:
➢Chemical or electrical communication between cells occurs at synapses:
Electrical synapses:
- Action potentials travel directly from the presynaptic to the postsynaptic cells via gap
junctions
Chemical synapses:
- More common than electrical synapses
- Postsynaptic chemically-gated channels exist for ions such as Na+, K+, and Cl- Depending on which gates open, the postsynaptic neuron can either depolarise
or hyperpolarise
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Events at the synapse:
1. Action potential coming down the axon depolarises the axon terminal
2. The depolarisation opens voltage-gated Ca2+ channels, and Ca2+ ions enter the cell
3. Calcium entry causes synaptic vesicles to fuse with the presynaptic membrane,
triggering exocytosis of their contents into the synaptic cleft
4. Neurotransmitter diffuses across the synaptic cleft, and binds with receptors on the
postsynaptic cell
Neurotransmitters:
- Acetylcholine: triggers contraction of skeletal muscles
- Glutamate: main excitatory neurotransmitter in the brain
- GABA: inhibitory neurotransmitter that triggers hyperpolarisation
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5. Neural Integration:
➢Neural integration occurs at the cellular level:
- Excitatory postsynaptic potentials (EPSP) depolarise the postsynaptic neuron
- Binding of neurotransmitters to postsynaptic receptors open gated channels
that allow Na+ to diffuse into the cell
- Inhibitory postsynaptic potentials (IPSP) hyperpolarise the postsynaptic neuron
- Binding of neurotransmitter to postsynaptic receptors open gated channels that
allow K+ to diffuse out of the cell and/or Cl- to diffuse into the cell
➢Potential depolarising = excitatory postsynaptic potential (EPSP)
➢Potential hyperpolarising = inhibitory postsynaptic potential (IPSP)
- This depends on the type of ion channel in the postsynaptic cell
- A postsynaptic neuron integrates incoming stimuli and ‘decides’ whether or not to fire
- Each EPSP or IPSP is a graded potential
- It varies in magnitude depending on the strength of the stimulus applied
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- The mechanism of neural integration is summation
- This is the process of adding and subtracting incoming signals
➢Summation: graded potentials (EPSPs and IPSPs) are summed to either
depolarise or hyperpolarise a postsynaptic neuron
Two types of summation:
1. Temporal Summation: repeated stimuli cause new EPSPs to develop before previous
EPSPs have decayed
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2. Spacial Summation: postsynaptic neuron stimulated at several different places
Summary:
Soma-dendrites
Axon
Analogue signals
Digital signals
Amplitude code
Frequency code
Electronic potentials
e.g. synaptic potentials, receptor
potentials, etc
Action potentials
Passive conduction
Active propagation
Ion channels open at rest (K+ and Cl-)
Ion channels open at rest, and are also
voltage gate-able (Na+ and K+)
Attenuation and distortion with distance
All-or-none regenerative
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Reflex action:
Withdrawal reflex:
- Sensory receptors ➞ sensory neurons ➞ interneurons ➞ motor neurons ➞ effectors
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Sensory Reception:
Sensory Receptors Transduce Stimulus Energy and Transmit Signals to the Nervous System:
- Sensations are action potentials that reach the brain via sensory neurons
- Perception is the awareness and interpretation of the sensation
Transduction of Stimulus Energy and Transmission of Signals:
- A transducer is a mechanism that translates energy or signals of one form into a
different kind of energy or signals
- Sensory receptors convey the energy of stimuli into the embrace potentials and they
transmit signals to the nervous system
- This involves detection of stimulus energy, sensory transduction, amplification,
transmission, and integration
Stimulus energy:
External signal
Radio waves
Receptor
Transducer
A radio
Amplifier
Response
Sound waves
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Sensory transduction:
- The conversion of stimulus energy into a change in membrane potential
- Receptor potential is a sensory receptor’s version of a graded potential
Amplification:
- The strengthening of stimulus energy that can be detected by the nervous system
Transmission:
- The conduction of sensory impulses to the central nervous system (CNS)
- Depending on the sensory receptors:
- The strength of the receptor potential affects the amount of neurotransmitter
released by the receptor
- Intensity of receptor potential affects the frequency of action potentials
Integration:
- The processing of sensory information begins at the sensory receptor
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Sensory Receptors:
➢Sensory receptors are categorised by the type of energy that they transduce:
Types of Sensory Receptors:
- Mechanoreceptors: respond to mechanical energy
- For example:
- Muscle spindles respond to stretching of skeletal muscles
- Hair cells detect motion
- Chemoreceptors: respond to chemical stimuli
- Internal chemoreceptors response to glucose, O2, CO2, and amino acids
- External chemoreceptors are gustatory receptors (found in the mouth) and olfactory
receptors (found in the nose)
- Thermoreceptors: respond to heat or cold (they respond to both surface and body core
temperatures)
- Electromagnetic receptors: respond to electromagnetic energy
- Photoreceptors: respond to radiation (visible light)
- Electroreceptors: respond to electric currents to locate objects (e.g. some fish use
electroreceptors to detect other fish)
- Tonic receptors: convey information about the duration of the stimulus
- Phasic receptors: rapidly adapt to a stimulus
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Vertebrate Nervous System:
The Vertebrate Nervous System Consists of:
Central Nervous System (CNS):
- Brain
- Dorsal, tubular spinal cord
Peripheral Nervous System (PNS):
- Sensory receptors
- Nerves
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The Brain:
Forebrain:
- Cerebrum: has of two hemispheres consisting of grey and white matter
- Left hemisphere is more adept at language, mathematics, and logical operations
- Right hemisphere is stronger at pattern recognition, nonverbal thinking, and
emotional processing
- Thalamus: relays motor and sensory signals to the cerebrum
- Hypothalamus: maintains homeostasis
Midbrain:
- The midbrain connects the forebrain to the hindbrain
Hindbrain:
- Pons and Medulla Oblongata: relay stations for information travelling between the
peripheral nervous system and the cerebrum
- Cerebellum: co-ordinates motor, perceptual and cognitive functions
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In the Motor Cortex and Somatosensory Cortex:
- Neurons are distributed according to the part of the body that generates sensory input
or receives motor input
The Spinal Cord:
Structure of the Spinal Cord:
Grey Matter:
- Composed of Glial cells, and is made up primarily of neural cell bodies
White Matter:
- Composed of Schwann cells, and consists of bundled axons
- Ascending tracks: transmits information to the brain
- Descending tracks: transmits information from the brain
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Peripheral Nervous System:
Peripheral Nervous System
Sensory (afferent) division
Sensing external
environment
Motor (efferent) division
Sensing internal
environment
Autonomic nervous
system
Parasympathetic
division
Somatic nervous
system
Sympathetic
division
- Autonomic Division: regulates the internal activities of the body (responding to visceral
stimuli)
- Somatic Division: responds to external stimuli (sensory organs)
- Parasympathetic System: influences organs to conserve and restore energy
- Sympathetic System: permits the body to respond to stressful situations
Sympathetic and Parasympathetic Nerves:
- Innervate many organs
- Functions in opposite ways; for example:
- Sympathetic system increases heart rate
- Parasympathetic system decreases heart rate
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Muscular System:
Types of Muscles:
Smooth Muscle: contracts involuntarily
Cardiac Muscle: contracts involuntarily
Skeletal Muscle: under voluntary control, and is essential for locomotion
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1. Striated Muscles Move Skeletal Parts by Contracting:
- Muscles come in antagonistic pairs
- i.e. in joints, one muscle attaches to one side of the joint, and another muscle
attaches to the other side of the joint (e.g. extender and flexor muscles)
Structure and Function of Vertebrate Skeletal Muscle:
- The sarcomere is the functional unit of muscle contraction
- Within the sarcomere, there are:
- Thin filaments consisting of two strands of actin and one tropomyosin are
coiled about each other
- Thick filaments consisting of myosin molecules
➢Actin and myosin are always the same length within the sarcomere
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Sarcomere:
- Reticulum: little net
- Terminal cisterna: storage sacs
- Sarcoplasmic reticulum: adapted for Ca2+ storage and release
- Sarcolemma: plasma membrane surrounding the muscle
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2. Interactions Between Myosin and Actin Generate Force During
Muscle Contraction:
- The sliding-filament model of muscle contraction
➢This is our understanding of what is happening to muscle fibres at a molecular level
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Length-Tension Relationship in Contracting Muscles:
➢The thinner the sarcomere gets, the greater the overlap of the thin and thick muscles
(greater tension = greater overlap)
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3. Calcium Ions (Ca2+) and Regulatory Proteins Control Muscle
Contraction:
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Energy Transduction in Muscles:
Electrical:
- Single nerve action potential arrives at the axon terminal to trigger the release of
acetylcholine
Chemical:
- Action potential releases a neurotransmitter, which triggers depolarisation
Electrical:
- An endplate potential is converted into an all-or-nothing action potential
Electrical:
- All-or-none muscle action potential triggers individual muscle contractions
Excitation-Contraction Coupling Process Occurs
Mechanical:
- Mechanical contraction of the muscle triggers a single twitch contraction
Relaxation of the Muscle Occurs
Control of Muscle Contraction:
- At rest, tropomyosin blocks the
myosin binding sites on actin
- Calcium binds to the troponin
complex to expose myosin binding
sites
- When an action potential meets the
muscle cell’s sarcoplasmic
reticulum, stored Ca2+ ions are
released into muscle fibres
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Review of Skeletal Muscle Contraction:
Events Controlling a Contraction of a Skeletal Muscle:
1. Endplate Potential (EPP) ➞ Muscle Action potential (MAP)
2. Signal conducted along T-tubules
3. Signal spreads from T-tubules to sarcoplasmic reticulum
4. Release of Ca2+
5. Calcium binds to troponin and a conformational change takes place
6. Change in position of the tropomyosin molecule
7. Cross bridges attach to the actin filaments
8. Active sliding of actin filaments into the A-band
9. ADP is released – the myosin head detaches from the actin filament (during a single
contraction, each cross bridge attaches, pulls and detaches many times)
10. Active calcium uptake by the sarcoplasmic reticulum – tropomyosin inhibits cross
bridges, causing the muscle to relax
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4. Diverse Body Movements Require Variation in Muscle Activity:
- An individual muscle cell (fibre) either contracts completely, or not at all
- Individual muscles, composed of many individual muscle fibres, can contact to varying
degrees
Three Phases of a Muscle Twitch:
1. Latent period: first few milliseconds after stimulation when excitation-contraction
coupling is taking place
2. Period of contraction: cross bridges actively form and the muscle shortens
3. Period of relaxation: Ca2+ is re-absorbed into the sarcoplasmic reticulum, and muscle
tension goes to zero
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Graded Muscle Responses:
- Variations in the degree of muscle contraction
- Required for proper control of skeletal movement
- Responses are graded by changing:
- Frequency of stimulation
- Strength of the stimulus
Tetanus Definition:
- The prolonged contraction of a muscle caused by rapidly repeated stimuli
Muscle Response:
- Threshold stimulus: the stimulus strength at which the first observable muscle
contraction occurs
- Beyond threshold, the muscle contracts more vigorously as stimulus strength is
increased
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Muscle Tension Depends On:
1. Frequency of stimulation
2. Number of motor units involved
- Graded muscle contraction is also controlled by regulating the number of motor units
involved in the contraction
- Each motor unit controls between four and a few hundreds of fibres
- The force of contraction is controlled by multiple motor unit summation, called
recruitment
- Recruitment of motor neurons increases the number of muscle cells involved in a
contraction
- Some muscles are always at least partially contracted (e.g. muscles responsible for
maintaining posture)
- Fatigue is avoided by rotating among motor units
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Two Types of Muscle Contractions:
- Isometric contraction: increasing muscle tension (the muscle does not shorten during
the contraction)
- Isotonic contraction: decreasing muscle length (muscle shortens during contraction)
- Fast muscle fibres are adapted for rapid, powerful contractions
- They become fatigued relatively quickly
- Slow muscle fibres are adapted for sustained contraction
- Relative to fast fibres, slow fibres have:
- Less sarcoplasmic reticulum ➞ Ca2+ remains in the cytosol longer
- More mitochondria present
- A better blood supply
- Myoglobin
Musculoskeletal System:
Antagonistic Action of Skeletal Muscles:
- Agonist muscle contracts
- Antagonist muscle relaxes
- These groups of muscles work together to allow for an overall movement of a joint
- Separately, closely timed stimuli produce smooth, sustained contractions
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Adaptations for Strength and Speed:
- Long muscles shorten faster
- Linear function of the number of sarcomeres
➢The longer and more elongated an animal’s legs, the faster they can run (in general)
Levels of Functional Organisation in a Skeletal Muscle:
- Muscles consist of bundles of muscle fibres (fascicles)
- Each fascicle has individual muscle fibres
- Each muscle fibre contains hundreds of myofibrils, and is innervated by a motor
neuron
- Myofibrils are bundles of myofilaments (actin and myosin)
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The Endocrine System:
The Endocrine System Consists of:
- Neurotransmitters: sends local chemical messages across a synapse
- Neuropeptides: generated in axon terminals – they are very similar to neurotransmitters;
however, they enter the blood stream to a target cells in different organs
- Hormones: regulatory substance that is transported in tissue fluids to stimulate specific
cells or tissues
- Pheromones: chemical substance produced and released into the environment by an
animal, affecting the behaviour or physiology of others of the same species
Glands:
- Exocrine glands: secrete their products outside the body via ducts
- Endocrine glands: secrete their products into the blood; however, they do not contain
ducts
➢Humans have nine endocrine glands
Page 85
Hormone Properties:
1. Hormones are produced and secreted by endocrine cells
2. They circulate in the blood and reach all tissues
3. They react with specific receptor molecules present in certain target cells
4. A single hormone may have multiple effects on the receiving target cell
Chemical Classes of Hormones:
- Polypeptides (proteins and peptides)
- Amines derived from amino acids
- Steroid hormones (derived from cholesterol)
- Prostaglandins (fatty acids)
Mechanism of Hormone Control:
1. Fixed Membrane Receptor Mechanism:
- Receptor in found in the plasma membrane
- Proteins and amines are water soluble, and are thus dissolved into the blood
➢Many transduction signals are needed in order to receive a response
Signal transduction
triggered by a cell-surface
hormone receptor
Page 86
2. Mobile Receptor Mechanism:
- Intracellular receptor
- Steroids are lipid soluble, and can thus move through the phospholipid layer of a cell
membrane
Direct regulation of gene
expression by a steroid
hormone receptor
Multiple Effects of Hormones:
- The same hormone may have different effects on target cells that have:
- Different receptors for the hormone
- Different transduction pathways
-
Page 87
Different signal transduction pathways in different cells can lead to different responses
to the same signal
- Signal transduction pathways allow for small amounts of a hormone to have a large
effect
Page 88
Chemical Signals in Animals – The Vertebrate
Endocrine System:
Hypothalamus and Pituitary Gland:
➢The hypothalamus and pituitary integrate many functions of the vertebrate endocrine
system
- The hypothalamus integrates endocrine and nervous function
- Neurosecretory cells of the hypothalamus produce:
- Releasing hormones: stimulate the anterior pituitary (adenohypophysis) to
secrete hormones
- Inhibiting hormones: prevent the anterior pituitary from secreting hormones
- The posterior pituitary (neurohypophysis) stores and secretes hormones produced by
the hypothalamus
Page 89
Types of Hormones:
Posterior Pituitary Hormones:
Oxytocin: a peptide
- Stimulates contraction of the uterus and mammary glands
- Secretion is regulated by the nervous system
Antidiuretic Hormone (ADH): a peptide
- Promotes retention of water by the kidneys
- Secretion is regulated by water / salt balance
Page 90
Anterior Pituitary Hormones:
Non-Tropic Hormones (directly stimulate target cells to induce effects):
Growth Hormone (GH): a protein
- Stimulates growth and metabolism
- Secretion regulated by hypothalamic hormones
- Acts directly on tissues or via growth factors
Prolactin (PRL): a protein
- Stimulates milk production and secretion
- Secretion is regulated by hypothalamic hormones
Melanocyte Stimulating Hormone (MSH): a peptide
- May play a role in fat metabolism
Endorphins: peptides
- Inhibits pain perception
- Effects are mimicked by heroin and other opiate drugs
Page 91
Tropic Hormones (target other endocrine glands):
Follicle Stimulating Hormone (FSH): gonadotropin; glycoprotein
- Stimulates the production of sperm and ova
- Secretion is regulated by hypothalamic hormones
Luteinising Hormone (LH): gonadotropin; glycoprotein
- Stimulates the ovaries and testes
- Secretion is regulated by hypothalamic hormones
Thyroid Stimulating Hormone (TSH): a glycoprotein
- Stimulates the thyroid gland
- Secretion is regulated by thyroxine in the blood
- Secretion is regulated by hypothalamic hormones
Adrenocorticotropic Hormone (ACTH): a peptide
- Stimulates the adrenal cortex secretion of glucocorticoids
- Secretion is regulated by glucocorticoids and hypothalamic hormones
Page 92
Example: Regulation of Thyroid Hormone Secretion
Page 93
Neural Input
Hypothalamic Neurosensory Cells
–
–
Releasing and
Release-Inhibiting
Hormones
–
+
Anterior Pituitary Gland
Growth Hormone,
MSH, Prolactin
ACTH, TSH,
FSH, LH
Somatic NonEndocrine Target
Tissues
Somatic
Endocrine Target
Tissues
Page 94
Gonadal Steroids:
➢Secretion regulated by FSH and LH
Testes:
Androgens (e.g. testosterone): steroids
- Support the formation of sperm
- Promote development and maintenance of male sex characteristics
Ovaries:
➢Secrete oestrogens and progesterone
Oestrogens: steroids
- Stimulates uterine lining growth
- Promotes development and maintenance of female sex characteristics
Progestins (e.g. progesterone): steroids
- Promotes uterine lining growth
Page 95
Mammalian Reproduction:
↳ A complex interplay of hormones that regulate reproduction
The Male Pattern:
- Androgens secreted by Leydig Cells are responsible for primary and secondary sex
characteristics
- They are also responsible for sexual behaviour and general aggressiveness in males
Primary Sex Characteristics:
- Development of the vasa deferentia and other ducts
- Development of the external reproductive structures (testes, penis)
- Sperm production
Secondary Sex Characteristics:
↳ These characteristics start to become prevalent during puberty
- Deepening of the voice
- Facial, armpit and pubic hair growth
- Muscle growth
Page 96
Regulation of Reproduction in the Male:
Page 97
The Female Pattern:
a cyclic pattern of hormone secretion and reproductive events
- Humans and many other primates have menstrual cycles
- If pregnancy does not occur, the endometrium is shed through the cervix and
vagina, and this is the process of menstruation
- Other mammals have oestrous cycles
- If pregnancy does not occur, the endometrium is reabsorbed by the uterus
- This is associated with more pronounced behavioural cycles than the menstrual
cycle, and these animals experience more pronounced seasonal and climatic
effects than those associated with menstrual cycles
Development of Follicles in the Ovary:
Page 98
The Ovarian Cycle:
Follicular Phase:
- Several ovarian follicles begin to grow
- Usually only one follicle continues to develop; the others disintegrate
- Maturation of the follicle leads to the release of the ovum
- The follicular phase then ends with ovulation
Luteal Phase:
- Follicular tissue remaining in the ovary develops into the corpus luteum, which secretes
oestrogens and progesterone
The Follicular Phase of the Ovarian Cycle:
- Gonadotropin Releasing Hormone (GnRH) stimulates the secretion of small amounts of
FSH and LH
- FSH stimulates growth of immature ovarian follicles
- These growing follicles secrete small amounts of oestrogens
- This thus inhibits secretion of FSH and LH during the first 10 days, which in
turn causes a buildup of the endometrium
Page 99
- The rate of secretion of oestrogens by the growing follicle rises steeply after day 10
- This then stimulates the hypothalamus to secrete GnRH, and the stimulation of
GnRH further stimulates the secretion of high amounts of LH
- LH induces the final maturation of the follicle, and thus ovulation
- Following ovulation, LH stimulates the formation of the corpus luteum, and the corpus
luteum is stimulated to secrete oestrogens and progesterone
- The secretion of oestrogen and progesterone thus inhibits FSH and LH secretion
- Near the end of the luteal phase, the corpus luteum disintegrates, and
concentrations of oestrogens and progesterone decline abruptly
- This triggers the onset of menstruation
Page 100
The Reproductive Cycle of the Human Female:
Fertilisation:
- The corpus luteum does not disintegrate
- The secretion of oestrogen and progesterone continues
- The endometrium is maintained
- Under endocrine signal, Human Chorionic Gonadotropin (HCG) is produced by the
developing placenta
Menopause:
- Cessation of ovarian and menstrual cycles
- Usually occurs between ages 46 and 54 due to ovaries decreased responsiveness
to gonadotropins
Page 101
Mechanisms of Contraception:
Page 103
Ecology – Prof Francesca Parrini
Overview of Ecology:
➢Ecology is the scientific study of interactions between organisms and their environment
- Modern ecology includes observations of experimentation; for example:
- What environmental factors limit geographical distribution
- What factors (such as food, pathogens and other organisms) affect population size
Scientists classify matter into levels of organisation:
Organism ➞ population ➞ community ➞ ecosystem ➞ biosphere
↳ Ecological interactions occur at different scales
Organismal Ecology:
- Organismal ecology involves the sub-disciplines of evolutionary, behavioural and
physiological ecology
- It thus deals with the influence of the environment on an organism’s structure,
behaviour and physiology, and how these factors meet environmental challenges
- e.g. how certain individuals will select a mate
Population Ecology:
- Population: a group of individuals of the same species living in the same area; these
individuals will freely interbreed to produce fertile offspring
- Population ecology focuses on factors affecting population size over time
- e.g. the environmental factors affecting a certain species’ reproductive rate
Page 104
Community Ecology:
- Community: group of populations of different species living in the same area
- Community ecology examines interactions (such as predation and competition) between
species within an area
- e.g. factors influencing the diversity of species’ interactions in a certain area
Ecosystem Ecology:
- Ecosystem: community of organisms in an area, and the physical factors with which
they interact
- Ecosystem ecology emphasises energy flow and chemical cycling among various biotic
and abiotic components in an environment
➢Biotic = living organisms
➢Abiotic = non-biological, physical factors
- e.g. factors that control photosynthetic productivity
Landscape Ecology:
- Landscape (or seascape): mosaic of connected ecosystems
- Landscape ecology focuses on exchanges of energy, materials, and organisms across
multiple ecosystems
- e.g. the extent to which nutrients from terrestrial ecosystems affect nutrients within
a lake
Global Ecology:
- A biosphere is a global ecosystem – it is the sum of all the planets’ ecosystems
- Global ecology thus examines how the exchange of energy and materials influences
different organisms across the biosphere
- e.g. the effect that air circulation has on the distribution of certain organisms
Page 105
Ecosystems:
- We distinguish levels in an ecosystem based on the food on which organisms feed, as
well as the steps of energy transfer that occur
Energy Transfer:
Laws of Thermodynamics:
1st Law: (the principle of conservation of energy)
- Energy cannot be created or destroyed, only transferred from one form to another
2nd Law:
- Every energy transfer or transformation increases the entropy of the universe; we
therefore end up with less usable energy with which we started
Tropic Levels:
- This relates to the position that an organism occupies in the food chain, and it
determines the route of energy flow in that ecosystem
Producers ➞ primary consumers ➞ secondary consumers ➞
tertiary consumers ➞ quaternary consumers
Producers (Autotrophs):
- Producers capture energy directly from the sun through photosynthesis
- e.g. plants found on land, algae, and aquatic plants
Anaerobic Respiration Formula:
6CO2 + 6H2O + light energy ➞ C6H12O6 + 6O2
Page 106
Consumers (Heterotrophs):
- Consumers are not able to produce their own energy
- They use their energy for growth and maintenance
Cellular Respiration Formula:
C6H12O6 + 6O2 ➞ 6CO2 + 6H2O + ATP
Types of Consumers:
- Primary Consumers – herbivores
- Secondary Consumers – carnivores (eat herbivores)
- Tertiary Consumers – larger carnivores (eat other carnivores)
- Omnivores – all levels
- Detritivores – feed on waste and dead bodies of other organisms, i.e. scavengers,
bottom feeders, dung beetles, vultures, bacteria, fungi
Q: What determines the amount of energy captured by plants?
A: The extent of photosynthetic production sets the spending limit for an ecosystem’s
energy budget
Page 107
The Global Energy Budget:
- The amount of solar radiation reaching the Earth’s surface limits photosynthetic output
of ecosystems
- Most solar energy is absorbed, scattered, or reflected by clouds / dust
- Only a small fraction of solar energy actually strikes photosynthetic organisms,
and even less is of a usable wavelength (≈ 1% VIS)
Gross and Net Production:
- Total primary production is known as the ecosystem’s gross primary production (GPP)
- GPP is the conversion of light energy to chemical energy (from photosynthesis) per
unit time – it is the rate at which producers convert solar energy into biomass
- GPP is determined by the quantity of photosynthetic tissue, and the duration of
activity (season)
➢Plants have to do maintenance respiration (R) in order to survive
- Net primary production (NPP) = GPP – R
- NPP is the storage of chemical energy available to consumers, and is expressed as:
- The energy per unit area per unit time (J/m2.yr); or
- Biomass (mass of vegetation) added per unit area per unit time (g/m2.yr)
➢NPP is not the same as the total vegetation of biomass; it is the amount of new biomass
added per unit time
Page 108
Global NPP Variation:
- Due to a high level of sunlight, the tropical rain forests are the most productive
- Water is used in photosynthesis
- There is most sunlight and moisture found on the equator
Primary Production in Aquatic Ecosystems:
- There is small global contribution because of the small area (one tenth of tropical rain
forests)
- In marine and freshwater ecosystems, both light and nutrients control primary
production
- There is the largest global contribution because of the vast area
Page 109
Light Limitation:
- Depth of light penetration affects primary production in the photic zone of an ocean or
lake
Nutrient Limitation:
- More than light, nutrients limit primary production in regions of the ocean and in lakes
- Limiting nutrient = the element that must be added for production to increase in a
particular area
- Nitrogen and phosphorous often limit marine production
- Concentrations of nitrogen and phosphorus are usually low in the photic zone
because they are taken up by phytoplankton, and because detritus tend to sink
Q: Why are estuaries so productive?
A: High inputs of nutrients flow from nutrient-rich rivers – the nutrients in the bottom
sediments are stirred up
-
Page 110
Upwelling of nutrient-rich waters in parts of the oceans contribute to regions of high
primary production
➢5% of total ocean area; 25% of global marine fish catches
Lakes:
- Adding large amounts of nutrients to lakes has a wide range of ecological impacts
- In soma areas, sewage runoff causes eutrophication (an increase in concentration
of nitrogen and phosphorus, and a depletion of oxygen) of lakes, which can lead to
loss of most fish species
- In lakes, phosphorus is more of a limiting nutrient than nitrogen
- This has led to the use of phosphate-free detergents
Page 111
Primary Production in Terrestrial Ecosystems:
- In terrestrial ecosystems, temperature and moisture affect primary production on a large
scale
Page 112
Nutrient Limitations and Adaptations That Reduce Them:
- On a more local scale, soil nutrient is often the limiting factor in primary production
- In terrestrial ecosystems, nitrogen is the most common limiting nutrient
- Various adaptations help plants access limiting nutrients from soil:
- Some plants form mutualisms with nitrogen-fixing bacteria
- Many plants form mutualisms with mycorrhizal fungi; these fungi supply plants with
phosphorus and other limiting elements
- Roots have root hairs to increase surface area, and therefore increase the area that
they have available to absorb nutrients and water
Cycling of Matter and Nutrients:
- Matter (nutrients) cycle within and among ecosystems and biospheres; human activities
are changing these cycles
Water Cycle:
Water Reservoirs:
- The oceans contain 97% of the biosphere’s water; 2% is found in glaciers and polar ice
caps; and 1% is found in lakes, rivers and groundwater
- 0.024% of water on Earth is accessible and available; the rest of either too salty, too
deep, or made of ice
Page 113
Carbon Cycle:
Page 114
Nitrogen Cycle:
Phosphorous Cycle:
Page 115
Trophic Structure:
- This is the feeding relationships between organisms in a community
- Food chains link trophic levels from producers to top consumers
Food Webs:
- A food web is a branching food chain with complex trophic interactions
➢A food web describes the flow of energy and nutrients through an ecosystem or a
community; whereas a food chain is a linear path through a food web
Food Chain Vs Food Web:
Food Chain
Food Web
Page 116
Limits on Food Chain Length:
- Each food chain in a food web is usually only a few links long
- Two hypotheses attempt to explain food chain length: the energetic hypothesis, and
the dynamic stability hypothesis
- The energetic hypothesis suggests that the length of a food chain is limited by
inefficient energy transfer along a food chain
- For example, a producer level consisting of 100 kg of plant material can
support about 10 kg of herbivore biomass (the total mass of all individuals in a
population)
- The dynamic stability hypothesis proposes that long food chains are less stable
than short ones
➢Most data supports the energetic hypothesis
Ecological Efficiency:
- This is the amount of usable chemical energy that is transferred from one trophic level to
the next
Page 117
Implications:
Q: Why are there so few lions compared to wildebeest in Africa?
A: There is more energy available for lower levels; therefore, food chains can sustain a
much larger herbivore biomass than carnivore biomass
Q: Are large carnivores more prone to extinction than large herbivores?
A: Yes. There is less carnivore biomass present; therefore, there are less individual
carnivores
Species with a Large Impact:
- Certain species have a very large impact on community structure
- Such species are highly abundant, and they play a pivotal role in community
dynamics
Dominant Species:
- Dominant species are those that are the most abundant or have the highest biomass
- Dominant species exert powerful control over the occurrence and distribution of
other species
- One hypothesis suggests that dominant species are most competitive in exploiting
limited resources such as space, water or nutrients
- Another hypothesis suggests that they are most successful at avoiding predators
- An example of dominant species:
- Invasive species: typically introduced to a new environment by humans, and often
lack predators or disease
Page 118
Keystone Species and Ecosystem Engineers:
- Keystone species exert strong control on a community by their ecological roles
- In contrast to dominant species, they are not necessarily abundant in a
community
- Field studies of sea stars illustrate their role as a keystone species in intertidal
communities
- Ecosystem engineers (or foundation species) cause physical changes in the
environment that affect community structure
- For example, beaver dams can transform landscapes on a very large scale
Bottom-Up and Top-Down Controls:
- The bottom-up model of community organisation proposes a unidirectional influence
from lower to higher trophic levels
- In this case, presence or absence of mineral nutrients determines community
structure (including abundance of producers)
l
de
mo
mo
up
Bo
tto
m-
wn
-do
Top
de
l
➢ Nutrients ➞ Vegetation ➞ Herbivores ➞ Predators
- The top-down model (or the trophic cascade model) proposes that control comes from
the trophic level above
- In this case, predators control herbivores, which in turn controls primary producers
➢ Nutrients ← Vegetation ← Herbivores ← Predators
Page 119
Species Interaction:
Indirect:
- Facilitation: actions of one species change conditions to benefit another species
- Keystone species facilitate resources
Direct:
- Direct interactions can be:
- Positive, where one or both species benefit; neither are harmed – e.g. mutualism
(facultative; obligate); commensalism
- Negative, where one species is harmed, and the other benefits – e.g. predation;
herbivory; parasitism; competition
Competition:
- Individuals of one group suffer a reduction in fecundity, growth, or survivorship as a
result of resource exploitation or competition by another group of individuals
- Competition can also occur within the same species (interspecific), or between
different species (intraspecific)
- Interspecific competition (–/– interaction) occurs when a species competes for a
resource in short supply
Competitive Exclusion:
- Strong competition can lead to competitive exclusion; local elimination of a competing
species
- The competitive exclusion principle states that two species competing for the same
limiting resources cannot coexist in the same place
Page 120
Ecological Niches and Natural Selection:
- The sum of a species’ use of biotic and abiotic resources is called the species’
ecological niche
- An ecological niche = an organism’s
ecological role in its environment
- Ecologically similar species can
coexist in a community if there are
one or more significant differences
in their niches
- Resource Partitioning: differentiation of
ecological niches, enabling similar species
to coexist in a community
- A species’ fundamental niche is the niche potentially occupied by that species
- A species’ realised niche is the niche actually occupied by that species
➢As a result of competition, a species’ fundamental niche may differ from its realised
niche – e.g. the presence of one barnacle species limits the realised niche of another
species
Page 121
Niche Separation Among Large Savanna Predators:
- Resource Partitioning: species selection; preferred habitat; time of hunting
Predation:
- Predation (+/–): one species (the predator) kills and eats another species (the prey)
Predator-Prey Oscillations:
- Classic predator-prey cycles do not occur in African savannas
- This assumes only one primary prey species, and this is NOT true because of prey
switching
Ecosystem Engineers:
- Allogenic: physically modify the environment by mechanically changing / moving
materials
- Autogenic: modify the environment by modifying themselves – e.g. trees
Predation (Landscape of Fear):
- The impact of predators not only through prey capture, but also – more subtly – by
causing behavioural shifts in the prey
Page 122
Predator Avoidance (General):
Mechanical Defences:
- Discourages predation by either causing physical pain to the predator, or making it very
difficult for them to eat the prey – e.g. horns; shells; spines
Chemical Defences:
- Produced by many animals and plants as toxic repellents used to deter predators –
e.g. discharge of a skunk; ink of an octopus
Physical Defences:
- Some organisms camouflage themselves by changing their body shape and colouration
in order to avoid being detected
- Other species will use aposematic (bright) colouration to warn predators that they
either have a foul taste, or that they are toxic
Mimicry:
Page 123
Morphological
Behavioural
Horns
Gregarious (living in groups)
Camouflage
Vigilance
Speed (fly, run, swim)
Alarm calls
Shell / spines
Defensive behaviour
Aposematic colours (warning colours)
Co-Evolution Between Predators and Prey: Evolutionary Arms Race
- “Life-dinner principle”: prey run for their lives; predators run for their dinner
➢“A fox may reproduce after losing a race against a rabbit, but no rabbit has ever
reproduced after losing the race to a fox”
Parasitism:
- Parasitism (+/–): one organism (the parasite) derives nourishment from another
organism (the host), harming it in the process
- Parasites have:
- Complex life cycles, with many hosts
- The host has reduced survival, reproduction and density
Endoparasites vs Ectoparasites:
Endoparasites:
- A parasite that lives within the host
Ectoparasites:
- A parasite that feeds off the external surface of the host
Page 124
Herbivory:
- Herbivory (+/–): a herbivore eats parts of a plant or algae
- Plant defences:
- Thorns, shape and texture of the plant, secondary compounds, insects, growth
strategies, or low nutrients
Types of Defences:
Structural Defences:
- Fertile soils
- Nutrient loss not limiting (found in fine leafed savanna)
Chemical Defences:
- Nutrient poor soil
- Nutrient loss is disadvantageous
- This is found in broad-leafed savanna
- Digestibility reducers: tannins
- Toxins: interfere with liver / kidney / central nervous system function
- Carbon-based chemicals defences found in nitrogen-limited areas (e.g. tannins)
- Nitrogen-based chemicals defences found in carbon-limited areas (e.g. alkaloids)
Thorns:
- Penetrates mouth parts of herbivores
- Prevents branch stripping
- Plants can be either curved or straight
- Thorns slow down browsing by:
- Restricting bite size
- Increasing handling time
- Reducing intake
Page 125
Q: How effective are thorns?
A: Goats / giraffe were found to eat
more from branches without thorns than
branches that contained thorns
Induced Thorns:
- Increased thorn length
- Within tree differences
- Between tree differences
Mutualism:
- Mutualistic symbiosis, or mutualism (+/+), benefits both species
- Mutualism is common in nature
- Obligate – i.e. cellulose digesting micro-organisms in rumen
- Facultative – i.e. acacia and ants
- Some plant species have swollen thorns containing carbohydrate-rich nectar, and they
house stinging ants – the plants thus provide food and shelter to the ants, and the ants
provide the plants with protection
Commensalism:
- Commensalism (+/0): one species benefits, and the other is neither harmed nor helped
- This is very hard to document in nature
Page 126
Questions:
1. What are gross primary production and net primary production, and how do they
differ? Why is this an important measure?
- Gross primary production is the rate at which producers convert solar energy into
biomass / chemical energy. Net primary production is the amount of new vegetation
biomass added per unit time.
- It is important because the storage of chemical energy available to consumers
determines how may trophic levels can be sustained, or how many consumers there
are at each level.
2. How can the addition to excess nutrients to a lake threaten its fish population?
What is this phenomenon called?
- More nutrients can support a high biomass of producers (algae, aquatic plants);
when primary producers die, detritivores decompose them (they use oxygen)
depleting the water of much or all of its oxygen. Therefore, there is not enough
oxygen to support different fish populations.
- This process is called eutrophication.
3. The phosphorus (P) cycle differs from those of carbon and nitrogen in what way?
- It does not include the atmosphere.
4. The amount of energy moving through a food chain declines rapidly as trophic
levels increase. Explain why this is so.
- At each trophic level, most of the energy is lost through biological processes, such
as respiration or finding food. Only the energy that is directly assimilated into an
animal’s consumable mass will be transferred to the next level when that animal is
eaten.
Page 127
Populations and Life History Traits:
Distribution Patterns:
- Most species have clumped distributions, due to:
- Clumped resources
- Searching for an individual in a group is more effective
- Predator defence
- Hunting advantage
Demography:
- The study of population change over
time
- Number of individuals = (births +
immigration) – (deaths + emigration)
- Age structure – it is important to
know the ages of individuals in a
population, as it tells us about the
health and reproductivity of the
population
Page 128
Life Tables:
- This is an age-specific summary of the survival pattern and reproductive rate of a
population
- Following the fate of a cohort, a group of individuals of the same age
Example: life table for female Belding’s ground squirrels
Page 129
Survivorship Curves:
- Graphic way of representing the data in a life table
- There are three types of curves:
Type 1:
- Low death rates during early and middle life, then an increase in death rates among
older age groups
- Few offspring are produced, but they live to reach maturity
- High parental care
Type 2:
- The death rate is constant over the organism’s life span curves
Type 3:
- High death rates for the young, then a slower death rate for survivors
- Produce many offspring, but few survive
- Low parental care
➢Many species have intermediate survivorship curves
➢Birds: mortality is high among the youngest (type 3), but is fairly constant among adults
(type 2)
Page 130
Exponential Growth vs Logistic Growth:
- Carrying capacity, density dependence, and resource limitations
Exponential Growth:
- Increases under idealised conditions
- Rate of increase is at its maximum: rmax
↳ N = population size
r = individuals in the population
t = time
The Logistic Growth Model:
- Per capita, rate of increase declines as carrying capacity (K) is reached
- This adds an expression that reduces the rate of increase per capita as the number of
individuals in an area (N) approaches K
↳ Same formula as the
exponential growth model; but:
K = carrying capacity
Page 131
‘Trade-Offs’ and Life Histories:
- Organisms have finite resources – these involve trade-offs between survival and
reproduction
- K-selection (density-dependent selection): life history traits are sensitive to population
density
- r-selection
(density-independent selection): life history traits that maximise repro-
duction
r-selected
K-selected
Mortality
Often catastrophic;
May be density-dependent
Density-dependent
Population size
Variable in time;
Usually lies below K
More constant
At or around K (depends on
consistency of environment)
Competition
Variable
Usually high
Favours …
Rapid development
High r
Early reproduction
Small body size
Low parental care
Slower development
Greater competitive ability
Later reproduction
Larger body size
Higher investment
Lifespan
Short
Long
Consequence
Productivity
Efficiency
Factors that Regulate Population Growth are Density-Dependent:
- Density-dependent birth and death rates are affected by many factors, such as
competition for resources, territoriality, disease or predation
Page 132
The Human Population:
- Prehistory into modern history
- Stable growth
- Over the past 350 years, there has been:
- Rapid, exponential population growth
- Industrial revolution
- Developments in medicine
- Vaccinations
➢The current world population is estimated to be approximately 7.7 bIllion people
- Since the 1960s, there has been:
- A drop in growth rate (1962: 2.2% ; 2009: 1.2%)
- It is predicted to be 0.7% by 2020
- The cause of this:
- Disease (e.g. HIV)
- Voluntary population control
Regional Population Change:
- Stable populations:
- ↑ births = ↑ deaths … A
- ↓ births = ↓ deaths … B
- Region change from A to B = demographic transition
- This is associated with:
- Industrialisation
- Healthcare
- Sanitation
- Education (for women)
Page 133
- Industrialised nations are near equilibrium:
- This is due to some decreased births and increased deaths
- Less industrialised nations:
- Increased births and decreased deaths
- More people found in in less developed regions
- Role of family planning:
- Delayed reproduction
- Contraception
Population age structure pyramids:
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Climate and Biodiversity:
- Macroclimate: patterns on the global, regional, and landscape level
- Microclimate: very fine patterns; i.e. community of organisms underneath a fallen log
➢Climates give rise to predictable types of ecosystems (called biomes)
Observation: Predictable Patterns Of Ecosystem Distribution Across The Earth
Global Ecological Processes:
- Climate: the prevailing weather conditions in an area
- It is influenced by:
- Temperature
- Precipitation
- Air movements (wind)
- Sunlight (most important)
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Sunlight Determines Global Patterns:
↳ Latitudinal variation in sunlight intensity:
Tilt, Sunlight and Seasons:
↳ When the Earth is tilted towards the sun (i.e. summer), that
hemisphere experiences greater heating
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Milankovich Cycles:
Global Climate Patterns: Air Circulation and Precipitation
Acute angle = less intense heat
- The uneven heating of the Earth’s surface causes atmospheric circulation
- There is, therefore, greater heating at the equator than at the poles
- Thus, there is a net transfer of energy to the poles, and the transfer occurs
through circulation of atmosphere and oceans
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Global Wind Patterns:
- Differential heating of the Earth’s surface causes wind that circulates heat and moisture
- The above diagrams are models of the relationship between differential heating, the
movement of air, and pressure difference in a convective cell
- Cool air pushes the less dense, warm air upwards, which reduces the surface
pressure
- As the uplifted air cools and becomes more dense, it sinks, which increases the
surface pressure
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Seasons and Latitude:
The Only Determinants of Temperature:
Elevation:
- Air density and pressure decrease with elevation
- Decrease in pressure: air molecules move further apart – it decreases by
approximately 6ºC/km
- Decrease in density: there is a higher rate of heat loss, which leads to more
extreme temperature fluctuations
- Implications:
- Mountains have different temperatures to other places
- Temperature varies according to season, latitude, and altitude
- Rain-shadow effect from mountains
➢Rising air releases moisture on the windward side of a peak, and creates a ‘rain-shadow’
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Water Bodies and Temperature:
- Wind and temperature drive ocean currents
Q: Why is San Francisco so cold compared to London?
A: It is due to the ocean currents – the western side of Northern America has a colder
current which cools the area down quite considerably; and there is a warmer current in
Northern Europe, making it warmer compared to Northern America
Differential heating / cooling of land and large bodies of water:
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- Day: air rises over warm land and draws a cool breeze from the water across the land
- Night: land cools, air rises over the warmer water and draws cooler air from land back
over the water, which is replaced by warm air from offshore
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Global Biomes:
- Criteria for defining a biome:
- Largest land community on a continental scale
- Major climatic features
- Dominant life forms in a climax community
- No human influences
A climograph shows the
importance of climate
on the distribution of
biomes
- Conditions determine distribution:
- Climate, latitude, bedrock, seasonality
- Ecotones: areas of overlap; one biome grading into another
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Important Terms and Definitions:
- Biodiversity: the diversity of different species (species diversity), genetic variability
among individuals within each species (genetic diversity), and variety of ecosystems
(ecosystem diversity)
- Endemism: a species that is confined to a specific, relatively small geographic area, and
are not found anywhere else in the world
- Rarity: a species that has a very small number of organisms; they can be endemic
Biodiversity Hotspots:
- A biodiversity hotspot is a relatively small area with numerous endemic species, and a
large number of endangered / threatened species
- Criteria: >1500 plant endemics, and >70% primary vegetation lost
- There are 34 hotspots globally (it originally covered 15.7% of the earth’s surface, but
now only covers 2.3%)
- 86% of original habitats have been destroyed
- 77% of all terrestrial vertebrates found in hotspots
- >150 000 endemic plants, and 11 980 endemic terrestrial vertebrates are found in
hotspots
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Terrestrial Biomes:
- Tropical forest, savanna, desert, temperature grassland, temperature broadleaf forest,
northern carnivorous forest, tundra, high mountains, and polar ice
Aquatic Biomes:
- Lakes, wetlands, rivers and streams, estuaries, intertidal zones, ocean pelagic zone,
coral reefs, and marine benthic zone
South African Biomes:
Savanna:
Nama Karoo:
Herbaceous and
woody perennials
Herbaceous
perennials, and
shrubs
Grassland:
Herbaceous
perennial; biennial
Succulent Karoo:
Shrubs and
succulents
Fynbos:
Herbaceous and
woody perennials,
and shrubs
Thicket:
Forest:
Woody perennials
Dense, impenetrable vegetation
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Determinants of South African Biomes:
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South African Biomes (Continued):
Fynbos:
- Fynbos is found in mountainous areas, as it is better
conserved there
- Renosterveld is found in low lying areas where
there is fertile soil; but only 5% remains
Fynbos Threats:
- Habitat transformation ➞ housing and agriculture
- Afforestation
- Invasive aliens
Fynbos Ecology:
Flora:
- Incredible diversity (9000 spp; 70% endemic) ➞ spp = species
- Winter rainfall, summer drought
- Nutrient-poor soil
- Fire is very important
Fynbos Fire:
- Most plants are geared towards coping with fire
- Most fires take place in Autumn
- Flowers produce seeds before the fire
- The fire stimulates the plants to release seeds
- Germination of the seeds is cued by the chemicals found in the smoke
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Fauna:
- Few large animals are found in areas with fauna
- This is due to poor soil, poor vegetation, and thus poor forage
- Many smaller animals are found in areas with fauna; such as baboons, many rodents,
and many reptiles
- There is a high diversity of frogs – ½ of South Africa’s frog species (of which 29 are
endemic) are found in these areas
Fynbos: Flagship Species
Marsh rose (Orothamnus zeyheri)
Occurs only on the south slopes of Kogelberg
In 1968, only 10 plants remained
When the fire regime changed, the population increased
Bontebok (Damaliscus pygargus)
Endemic to the Western Cape
Threats: habitat loss, aliens, hybridisation with blesbok
Protected since the 1940s
Stag beetle (Colophon spp)
Wingless beetle
Found on isolated mountain tops
Collectors item (CITES III category)
Micro frog (Microbatrachella capensis)
Critically endangered – only four populations
remaining, covering <10 km2
Endemic to certain fynbos wetlands
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Succulent Karoo:
- Rainfall is ≈250 mm/year
- Most rain takes place in winter
- It has rich flora of succulents
- There is a high endemism (69%)
Animals Adapted to Arid Environments:
- Due to the hot, arid environments, some animals either migrate or hide in order to avoid
the heat
- For example, some mammals and reptiles stay out of the sun during the day and
become active at night in order to stay cool
➢Most plant species hide, as they are unable to migrate to another cooler area
- The Succulent Karoo is home to ⅓ of the world’s 10 000 succulents
- It mostly contains smaller, contracted succulents
- Crypsis (the ability of an animal to avoid observation or detection by other
animals) is very important for animals in the Succulent Karoo
Succulent Karoo Threats:
Farming:
- Wheat, potato
- Winter grazing for stock
Mining:
- Rich in minerals and diamonds
Ecotourism:
- Massive floral displays
- Collecting from artificial fields = threat
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Succulent Karoo: Flagship Species
Namaqua pollen wasp (Ceramius rex)
South Africa has one of the highest diversity
of pollen wasps in the world
Often flower specific
Three isolated refuge populations left
Desert rain frog (Breviceps macrops)
Survives by living under sand dune surfaces
Major threat: strip mining for diamonds
Granulated thick-tailed scorpion
(Parabuthus granulatus)
Most venomous scorpion in South Africa
Nama Karoo:
- The Nama Karoo makes up 25% of the land covering South Africa
- There is some degree of overlap in vegetation with the Succulent Karoo
- Low shrubs, with grasses, succulents, neophytes,
and annual forbs are found in the Nama Karoo
- Grassiness varies with rainfall and grazing
pressure
- Termites are responsible for most of the nutrient
cycling in the Nama Karoo
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Threats:
- Overgrazing of livestock
- Areas being cleared for agriculture
Nama Karoo: Flagship Species
Riverine rabbit (Bunolagus monticularis)
Most endangered mammal in South Africa:
<1500 remaining
Agriculture along old riverbeds destroys habitats
Feed on flowers, grass and leaves
➢These rabbits produce two types of droppings – hard droppings during the night to save
water, and soft droppings during the day, which they eat in order to receive certain
minerals and healthy bacteria
The Karoo padloper (Homopus boulengeri)
Endemic to the Nama Karoo
Very little known threats;
overgrazing may be a threat
Namaqua sandgrouse (Pterocles namaqua)
Adapted to the desert
Their breast feathers are able to carry water
Water holes ➞ over dispersion and
predators ➞ egg predation
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Forests:
- Highly fragmented – it is surrounded by agricultural
land
- It is the most vulnerable biome
- Forests are frost-free areas
Types of Forests:
Coastal Forests:
- Rainfall is >700 mm in summer
- These forests contain a lot of firewood and timber
Threats:
- Urbanisation
- Dune mining
- Agriculture
Afromontane Forests:
- Rainfall is between 700 and 2000 mm
- Water is the key limiting factor
- These forests contain fire safe habitats
- There is a lot of firewood and timber
Threats:
- Plantations of aliens (pine trees)
- Subsistence harvesting
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Sand Forests:
- Found in tropical climates
- There is a lot of species diversity
Threats:
- Firewood
- Grazing
Forests: Flagship Species
Samango monkey (Cercopithecus mitis)
Forest fragmentation limits movements
Forest decline = population decline
There is now a stable population
Cape parrot (Poicephalus robustus)
Endemic: <500 left
Yellowwood trees are important for
feeding and nesting
They are often kept as pets; therefore,
decreased population found in the wild
Pink velvet worm (Peripatopsis roseus)
Ancient link between insects and earthworms
Living fossils
Only found in one forest patch in KZN
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Thicket:
- In terms of vegetation, thickets contain elements from all seven biomes – e.g. trees,
plants, succulents, etc
- It is an important biome under climate change – because the vegetation is so thick,
thickets have a high CO2 storage capability (CO2 + genetic material)
- This biome should therefore be conserved
- It is under-represented in protected areas
- Most species are rich, woody plants
➢Maputuland, Pondoland, and Albany are biodiversity
hotspots
Thicket: Flagship Species
Tree dassie (Dendrohyrax arboreus)
Arboreal browser
Needs tree-cavities as shelter
Habitat destruction is a major threat
➢Arboreal = lives in trees
Addo dung beetle (Circellium bacchus)
Flightless dung beetle
Protected in Addo Elephant National Park
Slow reproduction; produce few offspring per year
Very vulnerable
Albany cycad
70 individuals left
Plants separated by >1 km
Specialist pollinators are extinct
Male to female ratio is 4:1 – poor seed set
Collectors and bush clearing are major threats
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Savanna:
- Savanna covers 46% of land area of South Africa
- Grasses cover more than 5%, and trees cover 5-75%
- Rainfall gradient: west-east
- Savannas contain the richest animal diversity
- There is a large variation in vegetation
- There are more than 5700 plant species; only the fynbos biome has more plant
species
Q: What factors predispose savannas to frequent fires?
A: Dry season; adequate fuel; thunderstorms with lightening; people with fire
Savannas and Fire:
Impacts on grasses:
- Dead biomass is removed, which speeds up recyclable processes
- Vulnerable parts at ground level or below are thus protected
- Grass is regenerated with the next rainfall
Impacts on trees:
- Kills seedlings and small saplings
- Herbivory maintains young trees in a ‘fire trap’
- ‘Fire trap’ = the hight above the ground at which a tree has to be in order to survive
a fire
- Exclusion of fires = encroachment
- Encroachment = thick and full vegetation due to a fire
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Savanna: Flagship Species
Starburst horned baboon spider
Largest spider in South Africa
Nocturnal; live in silk-lined burrows
Commercially threatened
Wild dog
Most endangered carnivore in South Africa
Threats: habitat destruction, persecution,
rabies, competition
Currently only viable population is found in the
Kruger National Park
Metapopulation approach
Grasslands:
- Cover 30% of South African land space
➢Savannas cover most South African land space, followed by grasslands and the
Nama Karoo
- Grasslands are the most threatened biome in South
Africa
- 60-80% is irreversibly transformed, and only 3% is
conserved
- Grasslands have high economic importance: mining,
agriculture, and forestry
- There are two types of grasslands:
- Montane grasslands
- Highveld grasslands
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Grassland and Fire:
- Vegetation could be the same as the savanna climatically
- Vegetation is maintained by frequent fires
- This prevents the establishment of seedlings
Fire and South African Biomes:
- Wildfire is a natural phenomenon in many environments
- Patterns and behaviour differs in different biomes
- African forests: fires are catastrophic and infrequent
- Savannas, fynbos and grasslands: fires are important and necessary
- Without fires, these three biomes would not be able to maintain their structure, and
they would not have the species diversity that they do have
Grassland: Flagship Species
Giant bullfrog
Shallow rain-filled pans for breeding
They use grasslands for foraging and dispersal
Threats: habitat destruction, persecution, illegal
pet trade
Karkloof blue butterfly
Intricate life cycle with a specific plant
and ant species
Threat: alien invasive plants
Blue crane
Endemic to South Africa
Occur mostly on private lands
Threats: power line collisions, trade, loss of
grassland breeding habitat
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Q: If we know what is happening to our environment, then why do we bother with
biodiversity?
A: There are firm links between a healthy environment and intact biodiversity state; the
state of biodiversity can be seen as a general indicator of environmental health.
Use of Biodiversity in Terrestrial Ecosystems:
- Wildlife ranching (game sale; hunting)
- Farming of wildflowers
- Harvesting of plants
- Plant resources (rooibos; hoodia; devil’s claw)
- Wood
Informal Resource Use:
- Wood (building material; firewood)
- Food
- Medicinal plants
➢Intact biomes or protected area networks produce approximately 100x more economic
benefits than alternative converted land use forms (ecosystem goods and services)
➢Conservation happens at a local scale
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South African Ecoregions:
Freshwater Ecoregion:
- Vulnerable to over-exploitation
- It is semi-arid, and has an unpredictable climate
- South Africa faces water shortages in future
Threats:
- Habitat degradation
- Pollution
- Alien species
Freshwater: Flagship Species
Cape clawless otter
Needs freshwater for food (fish and crabs)
Threats: water extraction; dams and alien
water-plants
African jacana
Aquatic habitats with floating water plants
Not endangered, but suitable wetlands are
becoming less
- Average rainfall = 860 mm of rain pear year
- South African rainfall = 500 mm of rain per year
- This makes South Africa semi-arid
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Estuarine Ecoregion:
- Unique habitat: interface between freshwater and saltwater
- Varying salinity with tidal action
- Unique challenge to animals living here
Threats:
- Coastal developments
Estuaries: Flagship Species
Knysna seahorse
Endemic to South Africa; found in Knysna and
Swartvlei estuaries
Threats: habitat degradation; shore development
Peringuey’s leaf-toed gekho
Lives in salt marshes
Only known from a few sites in the Eastern Cape
Marine Ecoregion:
- There are two major currents:
- Agulhas current transports tropical fauna
southwards
- Benguela current has frequent upwellings
(causes productive food chains)
Threats:
- Overfishing (especially abalone, lobster and linefish)
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Marine Ecoregion: Flagship Species
Southern right whale
They were almost been hunted to extinction
Started being protected in 1935
The population is growing at 7%; but the total
population is only 10-15% of the original
African penguin
Current threats: oil pollution, and overfishing
of food supply
Group
Number of South
African Species
% Endemism
Plants
23 420 (9%)
60%
Marine Invertebrates
8 859 (8%)
36%
Marine Fish
2 200 (15%)
13%
Amphibians
111 (2%)
56%
Reptiles
363 (5%)
36%
Birds
694 (7%)
8%
Mammals
258 (6%)
16%
➢South Africa is the third most biodiverse country in the world, after Indonesia and Brazil