U2T2 - Photosynthesis Flashcards
Photosynthesis
What is the equation for photosynthesis?
6CO2 + 6H2O -> C6H12O6 + 6O2.
What are the 3 stages of photosynthesis + how were they determined?
Light harvesting, light dependent reactions, light independent stage. Experiments using radioactive isotopes.
Describe the light dependent reactions.
Light energy harvested by photosystem 2 used to photoactivate electrons, passed to electron acceptor via redox reactions. Chlorophyll molecules act as reducing agents for acceptor (donate electrons), Energy level progressively lowers throughout so energy released to form ATP from ADP + Pi by phosphorylation. Electrons from PS2 replaces those lost from PS1, og electrons passed via acceptors + reduce H+ + NADP+. H ions, O2 byproduct + electrons from hill reaction by photolysis of water, completing reduction and replacing electrons lost in PS2.. Light absorbed by PS1 allows electrons to be raised to higher energy level to electron acceptor.
What is the equation for the reduction of NADP + H ions?
NADP+ + 2H+ + 2e- -> NADPH + H+
What is the equation for the hill reaction?
2H2O -> 02 + 4H+ + 4e-
Why do leaves appear green?
Chlorophyll reflects green light and absorbs red and blue light. Shown by absorption spectra.
Calvin Cycle:
How much of triose phosphate goes to lipids, carbs + proteins?
How much of triose phosphate goes to RuBP?
1/6
5/6
Describe the light independent stage/calvin cycle.
CO2 combines with 5C RuBP (CO2 acceptor), catakysed by RUBISCO. 6C compound formed short lived, breaks down to 2 3C GPs. Phosphorylated using ATP, reduced using NADPH, form 3C triose phosphate used to create organic molecules (Lipid, carb, protein) or regenerate RuBP.
How is the rate of photosynthesis determined?
Rate of O2 production or CO2 uptake (cm3hour-1). Governed by reactant availability. Overall determined by slowest reaction in pathway. i.e. low CO2, low fixation rate, CO2 is limiting factor.
What are some limiting factors of photosynthesis?
Light intensity, CO2, water, temperature.
Why would a plant have a lower compensation point?
If it is a shade plant and needs less light intensity, adapted to photosynthesise more in lower light than higher light.
Describe the site of photosynthesis.
Palisade layer with cells tightly packed with lots of chloroplasts in cytoplasm. Spongy mesophyll less tightly packed with lots of air spaces as continuous pathway to stomata, facilitating gas exchange.
What is the link between the light independent and dependent reactions?
When light removed, light dependent reaction stops so ATP + NADPH not made so light independent can’t occur. When CO2 not available, can’t be fixed so cycle stops.
Describe how light limits photosynthesis.
Limits it as without it, no ATP or NADPH is produced for GP to TP step.
Describe how CO2 limits photosynthesis.
Without it, RuBP has nothing to fix so no GP synthesised.
