Photosynthesis Flashcards
What is the equation for photosynthesis
6CO2 + 6H2O → C6H12O6 + 6O2
How does the structure of the leaf facilitate gaseous exchange?
The spongey mesophyll are loosely packed together with air spaces which allows the diffusion of gases
Describe the structure of the chloroplasts
The chlorophyll is arranged in a system of flattened membranes called thylakoids. This is where light is trapped. They also contain a system of electron carriers and associated enzymes involved in photosynthesis. Thylakoids arranged in clumps called grana.
Where does light harvesting and carbon fixing take place?
Light harvesting - thylakoids
Carbon fixing - Stroma
What is the absorption spectrum?
A graph that shows the relative absorption of light at different wavelengths
What is the action spectrum?
The rate of photosynthesis at different wavelengths of light
What are the three processes of photosynthesis
- Light harvesting - The absorption of light in the thylakoid. Raises electrons to a higher energy level
- Light dependent stage - Energises electrons used to make energy rich compounds of ATP and NADP. Occur at thylakoid membranes
- Light independent stage - Products of the light reaction are used to make simple carbohydrate. Occur in stroma
Describe the process of light harvesting
The chlorophyll is located in the thylakoid membranes, which are arranged in clusters called antenna complexes. Chlorophyll a called the primary pigment is situated at the reaction centre. Light is harvested over a range of wavelengths due to resonance transfer. Each antenna forms a photosystem.
Describe the light dependent stage
Occur in thylakoid membranes. If enough light energy present, the electrons in the primary pigment get excited to a higher energy level via photo-activation which is taken up by an electron acceptor. The electron admitted goes to an electron acceptor at the start of an ETC with cytochromes forming the chain itself. Carries are reduced an oxidised in a series of redox reactions. Each carrier is at a progressively lower energy level, and at certain points there is sufficient energy for ATP to be synthesised. The production of ATP is called photo-phosphorylation. The electrons admitted are replaced by the splitting of water, photolysis. Oxygen is a waste product. If photosystem 1 releases an electrons it is passed to NADP to form reduced NADP.
Describe the light independent stage
Takes place in the stroma and is dependent on ATP and reduced NADP. CO2 combines with RuBP to form 2 Glycerate phosphate. This is catalysed by rubisco. The ATP and reduced NADP are used to reduce GP to 2x Triose phosphate. 5/6 molecules of TP are recycled to RuBP, catalysed by ATP. 1/6 of TP is used to create useful organic compounds.
What happens when light is removed?
The light dependent stage stops. There is no more ATP and reduced NADP which causes a build up of GP and a reduction of RuBP as carbon is still fixed but it is not regenerated. Concentration levels off as process stops.
What happens when CO2 is removed?
When CO2 is no longer available it can no longer be fixed to RuBP, which means no GP is formed. RuBP builds up as GP is already in the system being converted to TP. Concentration levels off as the process stops.
What four factors affect the rate of photosynthesis?
- Light intensity - not enough ATP/NADPH produced
- CO2 concentration - If this is increased more is available for the fixing to RuBP, which means more GP and more glucose
- Temperature - If this is increased, the enzyme catalysed reaction of RuBP to GP occurs at a faster rate
- Shortage of water - If theres a shortage, stomata close which means no more CO2 can get in and RuBP is not converted to GP
What is the equation for gross photosynthesis?
Gross photosynthesis = net photosynthesis + Respiration
What is the compensation point?
The rate of photosynthesis = the rate of respiration
