Photosynthesis Flashcards
Where does photosynthesis take place?
Occurs in the leaf, in the chloroplasts
What is the equation for photosynthesis?
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
What is the granum?
A stack of about 100 thylakoids in the chloroplast
What is a thylakoid
A flat disk like structure
What is the stroma?
The fluid filled matrix of the chloroplast
Where does the light-dependent stage of photosynthesis take place?
In the membrane of the thylakoid
What is the purpose of the light-dependent stage?
To synthesise ATP
Which photosystem occurs first?
Photosystem 2
What is the name of the pigment found in photosystem 2?
P680
What is photoionisation?
Where light provides high energy to 2 electrons in a pigment so that they can be released
What accepts electrons in an electron transport chain?
Electron acceptors
What is ATP made from?
ADP + Pi
Where is ATP used after the LDR?
The Calvin Cycle
What is the difference between cyclic and non-cyclic photophosphorylation?
- Cyclic only occurs at photosystem 2
- After passing through the electron acceptor, they return to the chlorophyll they came from.
- Non-cyclic produces more ATP
What is the purpose of the light-independent reaction?
To synthesise useful organic molecules
Where does the carbon dioxide in the Calvin cycle come from?
The atmosphere. It diffuses into the leaf and through the membranes to get to the stroma
What is the name of the enzyme involved in the Calvin Cycle?
Rubisco
What reaction does rubisco catalyse?
RuBP + Carbon Dioxide
What is the product of the carboxylation of RuBP?
2 molecules of GP
Where does NADPH in the calvin cycle come from?
the light dependent reaction
What is the role of NADPH in the calvin cycle?
To reduce GP into TP (triose phosphate)
Where does NADP go after reducing GP?
To the light dependent reaction to be reduced again
What useful organic molecules can TP be converted to?
Starch, cellulose, glucose, amino acids and nucleotides
If not converted to an organic molecule, what happens to TP?
Converted into RuBP to start the cycle again
If light intensity was dramatically reduced, how would it affect the rate of photosynthesis?
- ATP and NADP levels will fall which will pause the LDR
- Conversion of GP to TP requires ATP, so this will slow the rate of the Calvin cycle
- RuBP levels will fall so there will be an increase of carbon dioxide in the chloroplast
- RATE DECREASES
If carbon dioxide levels rose dramatically, how would it affect the rate of photosynthesis?
-More carboxylation will increase levels of RuBP, GP & TP
-Will cause the stomata to open, which will cause water loss and wilting
- Carbon dioxide levels will reduce when the stomata close as a stress response
RATE DECREASES
If the temperature rises dramatically, how would if affect the rate of photosynthesis?
- High temps increase kinetic energy of molecules in LIR
- High temps also increase rate of transpiration, causes plants to wilt
- Stress reaction causes stomata to close and this reduces carbon dioxide availability
- Rubisco can denature
RATE DECREASES
Why is it beneficial that stomata are closed at night?
Plants can’t photosynthesise without light, water can be lost when the stomata open, to reduce water loss and maintain cellular water content the stomata will close.
