4 ATP and reduced NADP are the two main products of the light-dependent reactions of
photosynthesis, and they then pass to the light-independent reactions.
5 In the light-independent reactions, carbon dioxide is trapped by combination with a 5C
compound, RuBP, which acts as an acceptor molecule. This reaction is catalysed by the
enzyme ribulose bisphosphate carboxylase (rubisco), which is the most common
enzyme in the world. The resulting 6C compound splits to give two molecules of a 3C
compound, GP (also known as PGA). GP is reduced to carbohydrate, using ATP and
reduced NADP from the light-dependent reactions. This carbohydrate can be converted
into other carbohydrates, amino acids and lipids or used to regenerate RuBP. This
sequence of light-independent events is called the Calvin cycle.
6 Chloroplasts, palisade mesophyll cells and whole leaves are all adapted for the
efficient absorption of light for the process of photosynthesis.
7 When a process is affected by more than one factor, the rate of the process will be
limited by the factor closest to its lowest value. The rate of photosynthesis is subject to
various such limiting factors, including light intensity and wavelength, carbon dioxide
concentration and temperature.
8 A graph of the particular wavelengths of light that are absorbed by a photosynthetic
pigment is called an absorption spectrum, and a graph of the rate of photosynthesis at
different wavelengths of light is called an action spectrum.
9 The different pigments present in a chloroplast can be separated by paper
1. End-of-chapter questions
1 What are the products of the light-dependent reactions of photosynthesis?
A ATp, RuBP and reduced NAD
B ATp, oxygen and reduced NADP
C GP, oxygen and reduced NAD
D GP, reduced NADP and RuBP
2 Where in the chloroplast are the products of photophosphorylation used?
3 In parate
experiments, an actively photosynthesising plant was supplied with one of
two labelled reactants:
• water containing the 18O
• carbon dioxide containing the
In which products of photosynthesis would these isotopes be found?
6 2, 7, 4, 6, 3, 1, 5
All correct = 4, subtract marks for mistakes.
7 a allows chlorophyll and other pigments to be arranged into photosystems;
provides large surface area for pigments;
increases effi ciency of light harvesting; allows electron carriers to be arranged
appropriately; provides structure for proton gradient for chemiosmosis; anchors