Photosynthesis Flashcards
Describe the Calvin Cycle
- RuBP combines with CO2
- Rubisco fixes carbon
- unstable 6C compound formed
- Produces two molecules of GP
- GP is converted to TP by reduced NADP and ATP from light dependent stage
- TP used to regenerate RuBP
- Using ATP
- TP can form hexose/ fatty acids/ acetyl CoA
State exactly where the Calvin cycle occurs in plant cells
Stroma of chloroplast
How does non-cyclic photophosphorylation produce ATP and reduced NADP?
- PI and PII both involved
- Light harvesting clusters
- Light absorbed by accessory pigments
- Primary pigment = chlorophyll a
- Energy passed to primary pigment
- Electrons excited to a higher energy level
- Electrons taken up by electron acceptor
- Electrons pass down electron carrier chain to produce ATP
- Photosystem II has water splitting enzyme
- Water is split into protons, electrons and oxygen
- This is called photolysis
- Electrons then pass from PII to PI
- To replace those lost
- Protons and electrons combine with NADP to produce reduced NADP
Suggest and explain why the rate of photosynthesis of a plant falls to zero at just over 40 degrees
Optimum temperature for rubisco = 26degrees At 40 degrees, rubisco is denatured So less carbon fixed Reduction in Calvin cycle Increased rate of transpiration So stomata close Less CO2 uptake Oxygen more likely to combine with rubisco So increased photorespiration
Name the compound which combines with CO2 in the light independent stage in a C3 plant
Ribulose bisphosphate (RuBP)
Outline the role of reduced NADP in the light-independent stage
Converts GP to TP by reducing (donating a hydrogen)
Explain how the physiology of the leaves of a C4 plant such as maize is adapted for efficient carbon fixation at high temperatures
In C3 plants at high temperatures rubisco combines with oxygen
Less rubisco combines with CO2
In C4 plant such as maize rubisco in bundle sheath cells is kept away from oxygen
Mesophyll cells absorb CO2
CO2 released to combine with RuBP
Avoid photorespiration
High optimum temperatures of enzymes involved
Calvin cycle can continue
Describe how in photosynthesis light energy is converted into chemical energy in the form of ATP
- Light energy is absorbed by chlorophyll
- Electron excited to a higher energy level
- electron emitted by chlorophyll
- passes electron to electron carrier
- passes along chain of electron carriers
- energy released is used to pump protons
- into thylakoids space
- thylakoid membrane is impermeable to protons
- proton gradient forms
- protons move down gradient
- through ATP synthase
- enzyme rotates
- ATP produced from ADP and Pi (inorganic phosphate)
Outline how the biochemistry of C4 plants differs from C3 plants
In C4 plants the first product of photosynthesis is a 4-carbon compound, oxaloacetate (which is then converted to malate)
In C4 plants the first CO2 acceptor is PEP (in C3 plants it first combines with RuBP)
Describe the role of rubisco in the Calvin cycle
Rubisco fixes carbon dioxide by catalysing the reaction between RuBP and CO2 to give two molecules of GP via an unstable intermediate compound
Why does PEP carboxylase have a higher rate of activity in C4 plants?
Why does rubisco have a higher rate of activity in C3 plants?
C4 plants can live in higher temperatures
Rubisco has a higher rate of activity in C3 plants because there is more rubisco
Why can C4 plants afford the high cost of ATP?
C4 plants are adapted to high light intensities
so there is a high rate of photophosphorylation
so there is a lot of ATP produced
