Topic 5 Flashcards
1
Q
Give a DETAILED explanation of the light dependant reaction
A
- photo-step two absorbs light energy
- energy excites electrons in chlorophyll to a higher energy level (photoionisation)
- high energy electrons leave the chlorophyll and go into the thylakoid membrane along a series of carrier proteins called the electron transfer chain
- electrons are transferred from one carrier protein to the next in a series of redox reactions until they reach photo-step one, releasing energy as they do so
- H+ ions diffuse back across the thylakoid membrane through protein channels formed by ATP synthase (chemiosmosis)
- movement of protons through ATP synthase causes shape change that allows the enzyme to catalyse ADP+Pi=ATP, ATP is made by photophosphorylation
- in the thylakoid H2O is split in the presence of light (photolysis) so H+ can contribute to electrochemical gradient, oxygen diffuses out, and electrons transferred to photo-step two to replace the ones lost in photoionisation
- photo-step one also absorbs light causing photoionisation
- electrons from here and H+ from photolysis are used to reduce NADP
- ATP and reduced NADP (NADPH) move into stroma for Calvin cycle
2
Q
How many Calvin cycles are needed to produce one glucose molecule
A
6 Calvin cycles need to occur to generate enough TP (triose phosphate) to produce 1 molecule of glucose and regenerate all 6 RuBP molecules
3
Q
Is the Calvin cycle affected by temperature?
A
These are enzyme catalysed reactions so they ARE affected by temperature
4
Q
Give a DETAILED explanation of the Calvin cycle ( light independent reaction)
A
- CO2 diffuses into the stroma and reacts with RuBP (carbon fixation)
- reaction is catalysed by the enzyme rubisco
- produced an unstable six carbon molecule which splits to give two molecules of glycerate 3-phosphate
- reduced NADP loses hydrogen (oxidised) and GP gains hydrogen (reduced) to form TP. ( NADP is reformed)
- ATP is hydrolysed to ADP + Pi to release energy for this conversion
- TP is used to regenerate RuBP using the phosphate group from the hydrolysis of ATP
- some of the TP is used to make organic molecules like glucose
- glucose can be joined to produce starch which is stored in the stroma
