Photosynthesis Flashcards
What is photosynthesis?
A reaction where light energy is used to produce glucose in plants
The reaction equation
Carbon dioxide + water (+energy) → Glucose + Oxygen
Factors that determine the rate of photosynthesis
- Carbon dioxide conc
- Light intensity
- Temperature
How are the chloroplasts adapted for photosynthesis? {4}
- Contains stacks of thylakoid membranes, grana + provides a large surface area for the attachment of chlorophyll, electrons + enzymes.
- Network of proteins in the grana hold the chlorophyll in a very specific manner to absorb the maximum amount of light.
- The granal membrane has ATP synthase channels embedded allowing ATP to be synthesised + be selectively permeable to establish a proton gradient.
- Chloroplasts contain DNA + ribosomes to synthesise proteins needed in the LDR
Steps of light dependant reaction
- Light energy is absorbed by PSII which excites the e⁻ in chlorophyll. These e⁻ move to a higher energy level + are released from the chlorophyll and move down the ETC to PSI
- The leaving e⁻ need to be replaced so photolysis releases H⁺, e⁻ and O₂ using light energy
- The excited e⁻ lose energy as they move down the ETC. The energy used to transport H⁺ to thylakoid so there is a H⁺ gradient across the thylakoid membrane. H⁺ move down the conc gradient into the stroma via ATP synthase, helping the formation of ATP from ADP + Pi. (chemiosmosis)
- Light energy absorbed by PSI excites e⁻ to an even higher energy level. They are transferred to NADP with a H⁺ to form NADPH
Steps of light independent reaction
- Carbon dioxide that has diffused through the stomata is combined with RuBP in carbon fixation, catalysed by rubisco. 2 molecules of GP formed.
- NADPH reduces the GP, with energy being provided by ATP. This forms 2 molecule of TP. 2 ATP and NADPH used to produce ADP and NADP
- The hydrolysis of ATP from the LDR provides energy for the conversion of GP to TP. NADPH is converted to NADP. 5/6 of the carbons are used to regenerate RuBP while 1/6 is used to form an organic substance eg, glucose
How are lipids made from the Calvin cycle?
- Glycerol is formed from the synthesis of TP
- Fatty acids are formed from GP
How are amino acids made from the Calvin cycle?
- GP can be used in the synthesis of amino acids
How does light intensity affect the rate of photosynthesis?
- Only certain wavelengths of light are absorbed by chlorophyll a, b and carotene
- The higher the light intensity, the more energy provided for the light dependent reaction
How does temperature affect photosynthesis?
- If temp is too low, the enzymes responsible for photosynthesis are slow or inactive
- If temp is too high, these enzymes become denatured
- The stomata also closes at high temperatures to avoid water loss, which slows down the reaction
How does carbon dioxide affect the rate of photosynthesis?
- At higher conc. there is more carbon fixation, so the rate of the Calvin cycle increases
- At very high conc. the stomata is forced to open so more water is lost
- This causes the stomata to close again slowing down the rate of photosynthesis
How does chlorophyll concentration affect the rate of photosynthesis?
- High chlorophyll conc increases the rate
- More chlorophyll, more light absorbed, so LDR increases
How do glasshouses manage limiting factors?
- Carbon dioxide is added into the air to increase concentration
- Light can get through the windows or using lamps at night
- These glasshouses trap heat from the sunlight, can also use heaters and cooling systems to maintain optimum temp
What is cyclic phosphorylation?
- It only involves PSI
- Electrons are not transferred from PSII
What is the difference between cyclic and non-cyclic photophosphorylation?
- In cyclic photophorsylation there is no NADPH produced
- In cyclic photophorsylation the electrons are recyled
- No photolysis takes place
