Topic 5 - Photosynthesis Flashcards
What is photosynthesis?
A reaction where light energy is used to produce glucose in plants.
What are the two stages in photosynthesis?
The light dependent stage
The light independent stage
What factors affect the rate of photosynthesis?
Light intensity
Wavelength
Carbon dioxide concentration
Temperature
What is the structure and function of a chloroplast?
- contains stacks of thylakoids membranes called grana, which provide a large surface area for the attachment of chlorophyll, electrons and enzymes.
- there are ATP synthase channels embedded in the granal membrane to allow ATP to be synthesised.
Where does the light dependent and independent reactions occur?
Light dependent - thylakoids membranes
Light independent - stroma
What is the second stage (photolysis) of the light dependent reaction?
Water splits into using light. When split it produced 1 oxygen, 4 protons and 4 electrons. Oxygen diffuses out or is used for respiration. Electrons replace those lost from chlorophyll. Protons move into the stoma, later creating a proton gradient.
What is the first stage (photoionisation) of the light dependent reaction?
Chlorophyll absorbs light energy, causing the electrons to become excited.
What is stage three of the light dependent reaction?
Excited electrons move down a series of protein complexes. Where energy can be used to pump protons from the stroma to the thylakoid space.
What is stage 4 of the light dependent reaction?
The electron then moves down the chain. Here more photons of light are absorbed causing the electron to move back up to a high level of energy.
What is stage 5 of the light dependent reaction?
The electron moves along the chain to another complex where the electron combines with a proton to form hydrogen. This is used to reduce NADP to NADPH.
What is stage six of the light dependent reaction?
There is now a greater concentration of protons in the thylakoid space than the stroma. The movement of these protons drive the process of photophosphorylation where ATP synthase phosphorylates ATP from ADP + Pi.
What is the first stage (carbon dioxide fixation) of the light independent reaction?
Carbon dioxide is fixed with ribulose bisphosphate in a process known as carboxylation. The enzyme Rubisco catalyses this. A 6 carbon sugar is formed, it is unstable so forms 2 molecules of glycerate-3-phosphate.
What is the second stage (reduction phase) of the light independent reaction?
The 2 glycerate-3-phosphate contain a carboxyl group. NADPH reduces glycerate-3-phosphate, using energy provided from ATP. Creatin 2 triose phosphate.
What is the third stage (regeneration of RuBP) of the light independent reaction?
5 molecules of triose phosphate are used in order to regenerate 3 molecules of RuBP. The remaining ATP from the light dependent stage is now used.
What is the fourth stage (organic molecule production) of the light independent reaction?
2 molecules of triose phosphate can combine to form the intermediate hexose sugar fructose 1, 6 bisphosphate where after it forms molecules of glucose.
