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Introduction To Cell Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

Chloroplasts have a double membrane. Describe the features of the outer and inner membrane.

A

Outer - Contains porins and are permeable to small molecules.
Inner - Impermeable to ions.
A lumen separates these two membranes.

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2
Q

Define thylakoids.

A

They are stacked in grana and are loose stromal lamellae.

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3
Q

Describe the structure of a chloroplast.

A

They contain their own cpDNA and ribosomes. They have a maternal inheritance.

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4
Q

Define plastoglobuli.

A

Lipid granules.

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5
Q

The carbon compound in photosynthesis is what type of molecule?

A

A triose phosphate.

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6
Q

What is the balanced equation for photosynthesis in the presence of light and chlorophyll?

A

6CO² + 12H²O —> C6H12O6 + 6H²O + 6O²

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7
Q

What is the purpose of light reactions?

A

To make ATP and NADPH in thylakoid membranes.

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8
Q

What is the purpose of light-independent reactions?

A

They fix CO² to C compounds in stroma.

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9
Q

Define pigment.

A

Substances that absorb light.

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10
Q

What two colours does chlorophyll A absorb?

A

Red and violet.

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11
Q

Define accessory pigments.

A

They absorb other wavelengths.

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12
Q

What two colours does chlorophyll B absorb?

A

Blue and violet.

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13
Q

What colour does carotenoids absorb? What kind of role does this accessory pigment have?

A

Blue. It has a protective role.

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14
Q

Define absorption spectrum.

A

Light wavelengths absorbed by different pigments.

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15
Q

Define action spectrum.

A

Effectiveness of different wavelengths in driving photosynthesis.

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16
Q

Describe the structure of chlorophyll.

A

Porphyrin head - Contains electrons which are excited by light energy.
Hydrocarbon tail - Anchors chlorophyll in the hydrophobic membrane core.
Magnesium ion - The central coordinating ion.

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17
Q

What two complexes do photosystems entail?

A

Light harvesting complexes each of a few hundred chlorophyll A and accessory pigments.
Reaction centre complex of a chlorophyll A dimer to which energy is transferred. It has a primary electron acceptor.

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18
Q

PSI reaction centre chlorophyll A is at what absorption peak?

A

P700.

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19
Q

PSII reaction centre chlorophyll A is at what absorption peak?

A

P680.

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20
Q

PSI and PSII work together. What are they linked by?

A

Electron transport.

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21
Q

Which photosystem can work alone?

A

PSI.

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22
Q

Describe the four stages of the non-cyclic electron flow in PSII.

A
  1. PSII absorbs lights, raising electrons to a higher energy state in P680.
  2. Excited electrons are passed to a primary electron acceptor.
  3. Photolysis by the oxygen-evolving complex releases electrons, O and H+. The electrons reduce P680+ chlorophyll A, O forms O² and H+ accumulate in the lumen.
  4. Electrons are passed from phaeophytin down electron transport chain (ETC) to PSI. The released energy moves H+ into the lumen.
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23
Q

Describe the four stages of the non-cyclic electron flow in PSI.

A
  1. PSI absorbs photons which raises the electron energy state in P700.
  2. Excited electrons are passed to a primary acceptor.
  3. Electrons lost from PSI are replaced by PSII.
  4. Electrons move down electron transport chain to NADP+ making NADPH.
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24
Q

What is the first chemical energy product?

A

NADPH. It is a powerful reducing agent.

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25
Q

Describe the four stages of the cyclic electron flow.

A
  1. Photons excite electrons in PSI.
  2. Electrons intercept electron transport chain between PSII and PSI. Thus, the electrons are not passed to NADP+.
  3. The electrons cycle back to PSI.
  4. The only product is ATP.
26
Q

Describe the four stages of ATP synthesis.

A
  1. H+ accumulate in thylakoid lumen making the PH 5.
  2. H+ diffuse back to stroma down concentration gradient.
  3. Many go via ATP synthase, a transmembrane protein.
  4. ATP synthesised in stroma (chemiosmotic production).
27
Q

What is the second chemical energy product of light reactions?

A

ATP.

28
Q

State three ways in which a H+ gradient is created across the thylakoid membrane.

A
  1. Photolysis releases H+ into lumen.
  2. Energy released by non-cyclic and cyclic electron flow pumps H+ into the lumen.
  3. H+ are removed from stroma in NADPH synthesis.
29
Q

Describe a five step summary of light reactions.

A
  1. Light raises energy level of electrons in PSI and PSII.
  2. Electrons are passed to P700 and P680, then down the ETC in the thylakoid membrane which releases energy.
  3. The released energy pumps H+ into the thylakoid lumen.
  4. H+ diffuse back to stroma, making ATP.
  5. Some electrons are passed to NADP+, making NADPH.
30
Q

ATP production is powered by what two sources?

A

Non-cyclic electron flow = non-cyclic photophosphorylation.

Cyclic electron flow = cyclic phosphorylation.

31
Q

Define proton motive force.

A

Potential energy in H+ gradient.

32
Q

Define chemiosmosis.

A

Energy coupling mechanism that uses H+ gradient across membrane to drive cellular work.

33
Q

What are the four products of the light reactions?

A
  1. O²
  2. H+
  3. ATP
  4. NADPH
34
Q

Explain how the light and dark reactions are linked.

A

Light reactions passes ATP and NADPH to the Calvin cycle. The Calvin cycle passes ADP + Pi and NADP+ back.

35
Q

What is the starting and end compound in the Calvin cycle?

A

RuBP.

36
Q

What are the three stages in the calvin cycle?

A
  1. Carboxylation.
  2. Reduction.
  3. Regeneration.
37
Q

What is the simple meaning of carboxylation?

A

Carbon fixation.

38
Q

Describe the three stages of carboxylation.

A
  1. One CO² (C) attaches itself to a RuBP (5C).
  2. This is catalysed by RuBisCO (RuBP carboxylase-oxygenase).
  3. The reaction results in a 6C intermediate which is unstable.
  4. This splits into 2x 3C (phosphoglycerate)
39
Q

Describe the three purposes of RuBisCO.

A
  1. It catalyses the first major step of the Calvin cycle.
  2. It combines CO² and 5C (RuBP), making 2x 3C compounds in the C3 pathway of photosynthesis.
  3. It has oxygenase activity.
40
Q

Why is RuBisCO inefficient?

A

It fixes 3 - 10 CO² per second.

41
Q

Describe the three stages of reduction.

A
  1. Each 3-PGA get a Pi from ATP.
  2. The phosphorylated 3C compound is reduced by NADPH.
  3. The product is a triose (G3P). This is the product of photosynthesis.
42
Q

For every six G3P made, how many is used by a plan cell?

A

One.

43
Q

Describe the four stages of regeneration.

A
  1. RuBP must be regenerated for the cycle to continue.
  2. For every six G3P made, five are recycled.
  3. Carbon skeletons of 5x 3C G3P are rearranged to make 3x 5C RuBP.
  4. 3 RuBP will react with three new CO².
44
Q

To produce one G3P, what five stages must occur?

A
  1. Three CO² enter the cycle.
  2. Nine ATP are used up.
  3. Six NADPH are used up.
  4. Net output is one 3C G3P.
  5. G3P is converted to glucose, sucrose or starch.
45
Q

How does a plant respond to hot and dry conditions?

A

The stomata close to reduce H²O loss and CO² uptake is also reduced.

46
Q

What happens if there is a low CO² concentration and a high O² concentration in chloroplasts?

A

RuBisCO adds O² to 5C RuBP.

47
Q

What happens during photorespiration?

A
  1. One 3C 3-PGA enters the Calvin cycle.

2. One 2C molecule exits the chloroplast and is converted in mitochondria/peroxisomes to release CO².

48
Q

For what three reasons does photorespiration make photosynthesis less efficient?

A
  1. Less G3P is made.
  2. ATP is used up.
  3. Carbon is lost from the Calvin cycle.
49
Q

What are the three main photosynthesis pathways for carbon fixation?

A

C3, C4 and CAM.

50
Q

What is the most common pathway for carbon fixation in photosynthesis?

A

C3.

51
Q

What two pathways are the most efficient during photosynthesis in a hot and dry climate?

A

C4 and CAM as they both concentrate CO² round RuBisCO.

52
Q

What type of anatomy does a C4 plant have?

A

Kranz anatomy. It also has spatial displacement of carbon fixation from the Calvin cycle.

53
Q

What two distinct types of photosynthetic cells does C4 plants have?

A

Mesophyll cells and bundle sheath cells.

54
Q

Describe the C4 pathway for the mesophyll cell.

A

CO² + 3C PEP is catalysed by PEP carboxylase to 4C oxaloacetate.

55
Q

PEP carboxylase has a higher CO² affinity than what molecule?

A

RuBisCO.

56
Q

Describe the C4 pathway for the bundle sheath cell.

A

4C malate releases CO² to a higher CO² concentration near RuBisCO. The Calvin cycle occurs as C3. The energetic cost is 15 ATP per G3P.

57
Q

What is the energetic cost of ATP is C3?

A

9 ATP.

58
Q

What does CAM stand for?

A

Crassulacean Acid Metabolism.

59
Q

What type of plant does the CAM pathway occur?

A

In succulents e.g. cacti.

60
Q

Describe the five stages of the CAM pathway.

A
  1. Stomata open at night and shut in the day to reduce H²O loss.
  2. Carbon fixation and the Calvin cycle occur at different times.
  3. At night, CO² is taken in.
  4. 4C malic acid is stored in the vacuole.
  5. During the day, CO² is released near RuBisCO. The light reactions make ATP and NADPH so the Calvin cycle occurs.

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