Biology
Class Notes
4-2
Aim: Photosynthesis and Respiration
Topic: How do plants make their own food?
(A) Photosynthesis
 Use the energy of sunlight to convert water and carbon dioxide into
sugar and oxygen
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Carbon dioxide—plants get from air
Water—absorbed from the soil
Sugar and oxygen are produced
(B) Pigments
 In addition to water and carbon dioxide, photosynthesis requires light
and chlorophyll
 Plants get the sun’s energy with light absorbing molecules called
pigments
 Chlorophyll a and b
 Refer to TB pg 207 figure 8-5
 Since light is a form of energy when light is absorbed, so is energy
(C) Chloroplast
 Organelle where photosynthesis occurs
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Contains thylakoids: saclike membranes—arranged in grana—stacks
of pancakes
Proteins here arrange the pigments into photosystems
Stroma: region outside the thylakoid
(D) Stages
 1—Light Dependent—requires light
o The light is absorbed by chlorophyll
o Oxygen is released
 2—Calvin Cycle—does not need light
o Carbon dioxide is used to make sugars
(E) Factors
 1—water—raw material (refer to equation)
 2—temperature—enzymes need proper temperature
 3—intensity of light—more light, more photosynthesis