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photosynthesis Flashcards

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1
Q

what are the parts of photosynthesis?

A
  1. capturing light energy
  2. light dependent reaction
  3. light independent reaction
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2
Q

what is the purpose of photosynthesis?

A

to convert light energy into chemical energy that can be used to produce sugars and other organic molecules

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3
Q

briefly list the main parts of photosynthesis:

A
  1. photoionisation of chlorophyll
  2. electron transport chain
  3. photolysis of water
  4. chemiosmotic theory
  5. electrons and a proton transferred to NADP and produce reduced NADP (NADPH)
  6. Calvin Cycle
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4
Q

briefly describe the light dependent reaction:

A
  1. PSII absorbs light energy and excites two electrons which then leave the chlorophyll (photoionised chlorophyll)
  2. An electron carrier protein takes electrons from PSII to PSI down the electron transport chain
  3. To replace lost electrons light energy splits water into protons, electrons and oxygen (photolysis of water)
  4. As electrons move down the electron transport chain they lose energy and this energy is used to transport protons into the thylakoid so thylakoid has a higher proton concentration than the stroma (produces proton gradient)
  5. Thylakoid membrane has ATP synthase that moves protons down their concentration gradient (this process also produces ATP) - this is the chemiosmotic theory
  6. When light energy is absorbed by PSI, electrons are excited to an even higher energy level - these electrons (and a proton) are transferred to NADP (producing NADPH)
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5
Q

briefly describe the light independent reaction (Calvin Cycle):

A
  1. CO2 enters the leaf through stomata
  2. CO2 reacts with 5C compound RuBP (ribulose bisphosphate) - this reaction catalysed by enzyme rubisco (already in stroma)
  3. This forms an unstable 6C compound which immediately breaks down into 2x 3C molecule glycerate-3-phosphate (GP)
  4. For GP to turn into TP the hydrolysis of an ATP molecule is needed, as well as an H ion that comes from oxidising NADPH to NADP, this reduces GP to triose phosphate
  5. 1/6 triose phosphate molecules go to form glucose and other organic substances
  6. 5/6 TP molecules go to regenerate RuBP with ATP from the LDR
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6
Q

what does RuBP stand for?

A

ribulose bisphosphate

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7
Q

what is the role of RuBP in the Calvin cycle?

A

It reacts with CO2 to from an unstable 6C compound

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8
Q

what is RuBP?

A

a 5C compound

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9
Q

what is rubisco?

A

the enzyme that catalyses the reaction between CO2 and RuBP in the Calvin cycle

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10
Q

After the unstable 6C compound is formed in the Calvin cycle, what does this immediately break down in to?

A

2 glycerate- 3-phosphate (GP) molecules

3C molecule

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11
Q

What occurs to turn each GP molecule into TP in the Calvin cycle?

A
  • the hydrolysis of one ATP molecule for each GP
  • the oxidation of NADPH to NADP so the H ion can reduce each GP to TP

( so 2 ATP molecules hydrolysed and 2 NADPH molecules oxidised)

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12
Q

What process is the Calvin cycle a part of?

A

Photosynthesis

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13
Q

What is the cycle in the light independent stage of photosynthesis?

A

The Calvin Cycle

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14
Q

What happens to the triose phosphate molecules produced in the Calvin cycle?

A
  • 1/6 go on to form glucose or other organic substances

- 5/6 go to regenerate RuBP with energy from ATP produced in LDR

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15
Q

what are the 3 parts of the Calvin cycle?

A
  1. carbon fixation
  2. reduction
  3. regeneration
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16
Q

In few words describe the Calvin cycle:

A
  • CO2 reacts with RuBP with help of rubisco
  • unstable 6C compound
  • straight into glycerate-3-phophate
  • to turn the two GP into two TP requires hydrolysis of 2 ATP and oxidation of 2 NADPH (reduces GP)
  • TP then goes to make organic substances or to regenerate RuBP (which requires ATP)
17
Q

How many times does the Calvin cycle go round to produce one molecule of glucose?

A

6 times

18
Q

What is needed from the LDR to produce 1 molecule of glucose?

A

18 ATP + 12 reduced NADP

19
Q

Where does the light dependent reaction take place?

A

thylakoid membrane (chloroplast)

20
Q

Where does the light independent reaction take place?

A

the stroma of the chloroplast

21
Q

What is cyclic photophosphorylation?

A
  • Only produces a small amount of ATP
  • Only uses PSI
  • Is cyclic because the electrons from the chlorophyll aren’t passed on to NADP, instead are passed back to PSI via electron carriers
  • so are recycled repeatedly and can repeatedly flow through PSI
  • doesn’t produce NADPH or O2 just ATP
22
Q

What are the possible limiting factors of photosynthesis?

A
  • Light intensity
  • Temperature
  • CO2 concentration

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