Photosynthesis Flashcards
What are the adaptations of the structures of a chloroplast for photosynthesis?
- Thylakoid membranes: Folded membranes which contain photosynthetic proteins ( chlorophyll) + electron carrier proteins are embedded within these membranes, both involved in LDR. More foldings, more proteins so speeds up rate of LDR.
- Stroma: Fluid centre containing enzymes involved in LIR
- Inner + outer membrane: Controls entry + exit of substances
What is the light dependent reaction (LDR) and where does it occur?
First stage of photosynthesis, it occurs in the thylakoid membranes or grana and it requires light. Light energy and water are used to create ATP and reduced NADP which are needed for the light independent stage.
Explain the role of light in photoionisation
-Chlorophyll molecules in psII absorb energy from photons of light
- This excites electrons + they are moved to a higher energy level + are released from the chlorophyll molecule
Explain photolysis
Photolysis is the splitting of water with light. When water is split it produces 1/2 molecule of oxygen, 2 protons (2H+) and 2 electrons.
O2 can either diffuse out of stomata or is used in respiration.
Electrons replace those lost from chlorophyll
Protons are picked up by NADP forming NADPH
Explain Photophosphorylation
-Electrons that gained energy + left chlorophyll move along electron transfer chain in thylakoid membrane
- As they move along they release energy + some is used to pump protons across chloroplast membrane, resulting in high conc of protons in intermembrane space (electrochemical gradient formed)
- Protons move down conc gradient by facilitated diffusion and pass through enzyme ATP synthase, causing a change in shape to protein which provides energy to catalyse ADP + Pi —>ATP
-H+ + e- + NADP—> reduced NADP
What is the light independent reaction and where does it take place?
- Occurs in the stroma which contains enzyme Rubisco which catalyses the reaction
- Uses CO2, reduced NADP, + ATP —> used to form hexose sugar
- ATP is hydrolysed to provide energy for reaction + reduced NADP donates hydrogen ion to reduce GP
Explain Carboxylation/ carbon fixation
- CO2 diffuses through stomata into leaf + reacts with RuBP —>6C molecule which splits into 2GP (glycerate 3 - phosphate)
- Reaction is catalysed by enzyme Rubisco
Explain Reduction
- GP is reduced to triose phosphate (TP) using energy given off from breakdown of 2ATP from LDR + accepting protons from 2 reduced NADP from LDR
- This is a reduction reaction as a H is gained
Explain regeneration
- 5 molecules of carbon from TP are used to regenerate RuBP and this uses energy from ATP
- 1 carbon is removed each time cycle happens + once cycle occurs 6 times, there will be 6 carbon removed which can create useful organic substances like glucose
Identify the environmental factors that limit the rate of photosynthesis
- Temperature - Affects LIR as it’s an enzyme - controlled reaction so if it’s too cold, there is not enough kinetic energy + enzyme will work too slowly, but if it’s too hot, enzymes denature
- CO2 conc - Affects LIR as it’s one of the reactants that enter. The curve slowly increases but then plateaus as it’s no longer limiting factor so must be another factor
- LI - Affects LDR as involved in photolysis + photoionisation. At the start of curve, LI is limiting factor, then plateaus at high LI as it could damage the chlorophyll, so there’s another limiting factor
What are the agricultural practices used to overcome the effects of limiting factors?
- Artifical lighting to maximise the LI
- Heating to increase the temperature
- Burning fuel to release more CO2
- Farmers need to consider profit so need to make sure it’s cost effective + that they make more profit
Why was radioactively labelled carbon used in photosynthesis?
To identify the products (glucose) of the light independent stage of photosynthesis
What is the function of dehydrogenase in chloroplasts?
It catalyses the acceptance of electrons by NADP in the light dependent reactions
What is the purpose of DCPIP?
It is a redox indicator which is blue when oxidised + turns colourless when reduced. It can pick up electrons from LDR instead of NADP
What is the purpose of ammonium hydroxide?
It is alkaline so could denature the dehydrogenase enzyme. It can also accept electrons, so could pick up electrons instead of NADP + DCPIP
