Unit 4. Maintaining life
4.1 Plants and Water
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Importance of Water: All living things need water to dissolve chemicals for reactions (e.g.,
respiration), transport minerals, support structure, cool via evaporation, and as a reactant in
photosynthesis. Plants absorb water continuously through roots from soil spaces (air/water
between irregular rock particles).
cells
Special structure to support its functions
Root hair cell
Long, thin; large sap vacuole → increase are surface →
absorb water + minerals
Xylem
Water moves across root to central xylem vessels
4.2 Transpiration
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Process: Water from xylem enters leaf cells; evaporates from cell walls into air spaces;
diffuses as vapor through stomata (mostly underside) to atmosphere. Transpiration =
water vapor loss from leaves; pulls water up (transpiration stream).
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Leaf Structure Role: Upper epidermis (waxy, reduces loss); palisade/spongy layers
(chloroplasts use some water for photosynthesis); air spaces/stomata allow diffusion. Most
loss from underside (more stomata).
Wilting: Full vacuoles = turgid cells (support); low water = flaccid, plant wilts.
4.3 Excretion in Humans
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Definition: Excretion = removal of metabolic wastes (from cells/body) like CO₂ (lungs),
urea (liver from excess protein), excess water (kidneys). Not feces (undigested, never in
body).
Excretory (Renal) System: Kidneys filter blood (remove urea/excess water); urine (urea +
water) via ureter to bladder (storage); out via urethra. System: Kidneys → ureters →
bladder → urethra.
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Urea Formation: Excess amino acids (from proteins) deaminated in liver to urea (toxic if
accumulated); blood transports to kidneys.
Experiments/Activities: Matching game: Cards with key words (e.g., bladder, urea) and
definitions; pair them.
Key Facts: CO₂ from respiration; plants don't excrete urea (no excess protein intake).
Distinguish urea (waste) vs. urine (solution); ureter (kidney to bladder) vs. urethra (bladder
out).
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4.4 Keeping a Fetus Healthy
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Fetal Development: Fetus = unborn baby (9 months in uterus); relies on mother's blood
(via placenta) for nutrients/O₂ ; excretes wastes (CO₂ , urea) back. No direct blood mixing;
diffusion only.
Diet Importance: Balanced diet + extra for fetus. Key: Protein (growth, muscles,
hemoglobin); carbohydrate (energy via respiration, not excess); iron (hemoglobin);
calcium (bones/teeth); vitamins A (eyes/skin), C (immune/iron absorption), D
(calcium/bones). Foods: Meat/fish (protein/iron), dairy (calcium), fruits/veggies
(vitamins/carbs).
Smoking/Drugs Harm: Smoking: Carbon monoxide reduces O₂ (smaller babies); nicotine
damages vessels/addictive. Drugs: Diffuse to fetus; check medicinal (e.g., antibiotics OK,
aspirin maybe); avoid non-essential/illegal/alcohol/caffeine (harm development).
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Unit 5. Reactivity
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5.1 Reactivity and Displacement Reactions
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Reactivity Series:
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Displacement Reactions: More reactive metal displaces less reactive one from its salt
solution.
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General: Metal A + Salt of Metal B → Salt of Metal A + Metal B (if A > B in series).
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Example: Iron + Copper sulfate → Iron sulfate + Copper (Fe displaces Cu; solution
fades, copper coats iron).
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Equation: CuSO₄ + Fe → FeSO₄ + Cu.
○ No reaction if less reactive (e.g., Cu + FeSO₄ ).
Key Facts: Signs of reaction: Color change, precipitate, gas, temperature change. Use
series to predict outcomes.
5.3 Salts
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Definition and Uses: Salts = compounds from acids (replace H with metal). Examples:
NaCl (food flavor/preserve), MgCO₃ (gymnasts' grip), CaSO₄ (chalk), Al₂ (SO₄ )₃ (dye
fixer), CuSO₄ (seed fungicide), NH₄ NO₃ (fertilizer).
Acids and Salts:
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Acids contain H (e.g., HCl → chlorides like NaCl
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H₂SO₄ → sulfates like CuSO₄; HNO₃ → nitrates like KNO₃)
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Carbonic acid (H₂CO₃ from CO₂ + H₂O) → carbonates
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citric acid → citrates.
Making Salts (Metal + Acid): Reactive metals (above Cu) + acid → salt + H₂.
E.g. Zn + 2HCl → ZnCl₂ + H₂. Unreactive (Cu, Ag) don't react.
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Making Salts (Metal Oxide + Acid): Base (metal oxide) + acid → salt + H₂O.
E.g. CuO + H₂SO₄ → CuSO₄ + H₂O (heat, filter excess, evaporate).
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Key Facts: Salts in rocks (e.g., malachite = CuCO₃ ). Crystallisation for pure/large crystals.
5.4 Other Ways of Making Salts
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Metal Carbonate + Acid: Carbonate + acid → salt + H₂O + CO₂.
E.g., CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂; CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
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Applications: Acid rain erodes limestone (CaCO₃ ); ocean acidification harms coral
(CaCO₃ skeletons).
Neutralisation (Acid + Alkali/Base): Acid + alkali/base → salt + H₂O.
E.g., NaOH + HCl → NaCl + H₂O. Bases = metal oxides/hydroxides; soluble bases = alkalis.
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Insoluble bases (e.g., FeO, CuO) react but don't dissolve.
Key Facts: General: Acid + carbonate → salt + water + CO₂; acid + alkali → salt + water.
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5.5 Rearranging Atoms
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Atom Rearrangement: Reactions rearrange atoms; no atoms lost/gained. Elements in
reactants = elements in products (balanced equations).
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Conservation of Mass: Mass unchanged (law of conservation of mass). E.g., CaCO₃ +
2HCl → CaCl₂ + H₂O + CO₂ (closed system; open loses CO₂, appears decrease).
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○ Experiment: CaCO₃ + HCl in stoppered flask on balance (mass constant).
Conservation of Energy: Energy unchanged (law of conservation of energy); transferred
forms.
○ Exothermic: Releases energy (e.g., K + H₂ O; thermite; bond formation >
breaking).
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Endothermic: Absorbs energy (e.g., sherbet: NaHCO₃ + citric acid → sodium citrate
+ H₂O + CO₂; cools mouth).
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Experiments/Activities: Burn Mg in crucible (mass increases due to O₂ addition; Mg + O₂
→ MgO).
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Key Facts: Lavoisier discovered O₂ in burning/respiration.
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Unit 6. Sound and space
6.1 Loudness and Pitch of Sound
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Sound Production: Sounds originate from vibrations (rapid backwards and forwards
movement of objects, e.g., ruler, guitar string).
Loudness: Measures how quiet/loud a sound seems; depends on vibration distance (larger
= louder) and source distance (farther = quieter due to energy dissipation).
Amplitude: Maximum particle displacement in a sound wave (from rest to peak or trough);
larger amplitude = greater loudness. Waveform graphs show this (e.g., on oscilloscope).
Pitch: How high/low a sound is (musical scale); depends on vibration speed.
Frequency: Number of complete vibrations per second (Hz); higher frequency = higher
pitch (e.g., shorter ruler length = faster vibrations/higher frequency).
Oscilloscope: Device to display waveforms; compares amplitude (loudness) and frequency
(pitch).
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6.2 Interference of Sound
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Interference: When same-type waves (e.g., sound) meet; requires similar
frequency/amplitude for clear effects.
Reinforce: Peaks/troughs align; amplitudes add = larger amplitude/louder sound (e.g.,
concert loudspeakers create louder spots).
Cancel: Peaks meet troughs; amplitudes subtract to zero = no sound (e.g., noise-cancelling
headphones generate out-of-phase waves).
Analogy: Water waves from two sources show reinforcing (larger waves) and cancelling
(flat areas).
Applications: Wind instruments vary length for reinforcement via reflection; reflected
waves reinforce/cancel.
Experiments/Activities: Water waves with nails on wood (observe pattern); tuning forks
over adjustable pipe (find length for loudest reinforcement).
Key Facts: Complete cancel needs identical waves; reflections complicate real-world
cancelling.
6.3 Formation of the Moon
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Collision Theory (Giant Impact Hypothesis): ~4.5 billion years ago, Mars-sized Theia
collided with proto-Earth; debris formed ring, coalesced into Moon via gravity; Earth
reformed from combined material.
Supporting Evidence: Moon less dense/small iron core (like Earth's mantle); Moon rocks
once molten/similar composition to Earth; Moon recedes ~4 cm/year (consistent with postcollision); fits Solar System formation; similar collisions observed.
Contradicting Evidence: Earth surface not molten (should have been); Venus lacks moon
(expected from common collisions); Moon more Earth-like than Theia-like.
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Other Theories: Fission (Moon split from spinning Earth); capture (Moon asteroid trapped);
co-formation (formed together).
Experiments/Activities: Research evidence/sources; evaluate reliability/bias; report
preferred theory.
Key Facts: Moon recession measured accurately; theory best explains data.
6.4 Nebulae
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Nebulae: Vast, low-density clouds of dust/gas (mostly H, some He); particles sparse (Earthsized nebula ~few kg); sizes >10,000x Solar System.
Formation: Some from exploding giant stars (supernovae eject material).
Examples: Orion (northern hemisphere, visible naked eye winter); Carina (southern
hemisphere).
Stellar Nurseries: Some nebulae where gravity collapses gas/dust; increasing
mass/pressure/heat triggers fusion, forming stars (young stars illuminate cloud).
Experiments/Activities: Virtual tour/research types (include nurseries); Hubble Telescope
(space-based, no atmospheric distortion).
Key Facts: Northern/southern hemispheres divided by equator; Hubble provides detailed
images.
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6.5 Tectonics
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Plate Movement: Crust divided into tectonic plates on mantle; core (~5000°C) heats
mantle, causing convection currents (hot fluid rises, cools, sinks); currents drag plates
slowly (0.6-10 cm/year).
Evidence: Continental jigsaw fit (e.g., Africa/S. America coasts); fossil distribution
(Mesosaurus in both, couldn't cross ocean; Glossopteris across multiple); magnetic
alignment (crystals in rocks show past pole reversals; mid-ocean ridges have current
alignment, older rocks reversed); earthquakes/volcanoes cluster at boundaries.
Key Facts: ~183 pole reversals in 83M years (~450,000 years average); mid-ocean ridges
form new crust, pushing plates.
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