3 Photosynthesis
Photosynthesis is the energy transfer process that is the basis of nearly all life on Earth. It provides energy
directly or indirectly
... [Show More] to all the organisms in most food chains. In eukaryotes, the process occurs within
chloroplasts. Candidates should apply their knowledge of plant cells from Cell structure (Topic 1) and leaf
structure from Transport in plants (Topic 7) while studying photosynthesis. Various environmental factors
influence the rate at which photosynthesis occurs.
The practical activities in this topic give opportunities for candidates to plan investigations, analyse and interpret
data and evaluate experimental procedures and the quality of the data that they collect.
13.1 Photosynthesis as an energy
transfer process
Learning outcomes
Candidates should be able to:
1 describe the relationship between the structure of chloroplasts,
as shown in diagrams and electron micrographs, and their
function
2 explain that energy transferred as ATP and reduced NADP from
the light-dependent stage is used during the light-independent
stage (Calvin cycle) of photosynthesis to produce complex
organic molecules
3 state that within a chloroplast, the thylakoids (thylakoid
membranes and thylakoid spaces), which occur in stacks called
grana, are the site of the light-dependent stage and the stroma
is the site of the light-independent stage
4 describe the role of chloroplast pigments (chlorophyll a,
chlorophyll b, carotene and xanthophyll) in light absorption in
thylakoids
5 interpret absorption spectra of chloroplast pigments and action
spectra for photosynthesis
6 describe and use chromatography to separate and identify
chloroplast pigments (reference should be made to Rf
values in
identification of chloroplast pigments)
7 state that cyclic photophosphorylation and non-cyclic
photophosphorylation occur during the light-dependent stage
of photosynthesis
8 explain that in cyclic photophosphorylation:
• only photosystem I (PSI) is involved
• photoactivation of chlorophyll occurs
• ATP is synthesised
9 explain that in non-cyclic photophosphorylation:
• photosystem I (PSI) and photosystem II (PSII) are both
involved
• photoactivation of chlorophyll occurs
• the oxygen-evolving complex catalyses the photolysis of
water
• ATP and reduced NADP are synthesised
continued
13.1 Photosynthesis as an energy
transfer process continued
Learning outcomes
Candidates should be able to:
10 explain that during photophosphorylation:
• energetic electrons release energy as they pass through
the electron transport chain (details of carriers are not
expected)
• the released energy is used to transfer protons across the
thylakoid membrane
• protons return to the stroma from the thylakoid space by
facilitated diffusion through ATP synthase, providing energy
for ATP synthesis (details of ATP synthase are not expected)
11 outline the three main stages of the Calvin cycle:
• rubisco catalyses the fixation of carbon dioxide
by combination with a molecule of
ribulose bisphosphate (RuBP), a 5C compound, to yield two
molecules of glycerate 3-phosphate (GP), a 3C compound
• GP is reduced to triose phosphate (TP) in reactions involving
reduced NADP and ATP
• RuBP is regenerated from TP in reactions that use ATP
12 state that Calvin cycle intermediates are used to produce other
molecules, limited to GP to produce some amino acids and TP
to produce carbohydrates, lipids and amino acids
13.2 Investigation of limiting
factors
Learning outcomes
Candidates should be able to:
1 state that light intensity, carbon dioxide concentration and
temperature are examples of limiting factors of photosynthesis
2 explain the effects of changes in light intensity, carbon dioxide
concentration and temperature on the rate of photosynthesis
3 describe and carry out investigations using redox indicators,
including DCPIP and methylene blue, and a suspension of
chloroplasts to determine the effects of light intensity and light
wavelength on the rate of photosynthesis
4 describe and carry out investigations using whole plants,
including aquatic plants, to determine the effects of light
intensity, carbon dioxide concentration and temperature on the
rate of photosynthesis [Show Less]