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A LEVEL BIOLOGY > 2 - Photosynthesis (C1) > Flashcards

2 - Photosynthesis (C1) Flashcards

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1
Q

What are the names of several photosynthetic pigments?

A
  • Chlorophyll a
  • Chlorophyll b
  • Beta carotene
  • Xanthophylls
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2
Q

What is the function of photosynthetic pigments?

A
  • To absorb light energy and begin its conversion to storable chemical energy
  • Different pigments absorb photons at different wavelengths of light
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3
Q

Where does the light dependent reaction occur?

A

In the thylakoid membranes and thylakoid cavity

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4
Q

Where does the light independent reaction occur?

A

In the stroma

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5
Q

What substances may be manufactured from triose phosphate?

A
  • Glucose
  • Lipids
  • Amino acids
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6
Q

What are some similarities between chloroplasts and mitochondria?

A
  • Fluid filled central area = matrix/stroma where a biochemical cycle occurs
  • Small 70s ribosomes
  • Circular DNA
  • Inner and outer membranes
  • Stalked particles
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7
Q

What does the action spectrum show?

A

A graph showing the rate of photosynthesis at different wavelengths

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8
Q

What is the absorption spectrum?

A

A graph showing how much light a particular pigment absorbs at different wavelengths

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9
Q

What is the bottom half of the cone shape of a photosystem?

A

Antennae complexes

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10
Q

What is the top of the cone shape of a photosystem?

A

Reaction centre

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11
Q

Why does increasing light intensity increase the rate of photosynthesis?

A
  • More photons trapped by photosynthetic pigments causes release of more O2
  • More NADPH and ATP is made which allows more turns of the calvin cycle etc.
  • Also more light = more stomata open = increased O2 uptake
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12
Q

What happens when light is a limiting factor?

A

There’s a build up of GP as there is insufficient ATP or NADPH to convert it further

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13
Q

What happens when there is excess light?

A

The pigments are damaged and the rate of photosynthesis is reduced

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14
Q

Why does increasing the temperature nearer to the optimum increase the rate of photosynthesis?

A

As the enzymes in the Calvin cycle can work in optimum conditions

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15
Q

Why does increasing CO2 conc increase the rate of photosynthesis?

A
  • Without CO2 the Calvin cycle can’t turn and there’s a build up of RuBP
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16
Q

What happens when there is excess CO2?

A

Stomata are closed

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17
Q

Why can water availability act as a limiting factor?

A

As a lack of water causes stomata to close, which restricts the plants CO2 intake and so its ability to carry out photosynthesis is restricted

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18
Q

What is chlorosis?

A

Yellowing of plant leaves due to a lack of chlorophyll production

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19
Q

What is nitrogen used for by the plant?

A

It’s used in the synthesis of proteins, nucleic acids and chlorophylls

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20
Q

What is magnesium used for by the plant?

A

It’s used to make chlorophyll

21
Q

What is a compensation point?

A

The light intensity on the light curve where the rate of photosynthesis is the same as the rate of plant respiration

22
Q

Why would the compensation point never be reached at night?

A

Because there is no sunlight at night so the rate of photosynthesis is greatly reduced, however the rate of respiration is greater and remains at this rate throughout the night, so there is no point where they are equal at the same time

23
Q

What is the dependent variable?

A

The variable being measured

24
Q

What is the independent variable?

A

The variable being changed

25
Q

Why do most leaves have a green colour?

A

They contain chlorophyll pigments that reflect green light

26
Q

When does cyclic photophosphorylation occur?

A

When there is sufficient NADPH2

27
Q

What does photolysis of water produce?

A

1/2 O2 + 2H + 2e

28
Q

What happens in the light dependent stage of photosynthesis?

A
  • Light hits PSII causing it to become excited and release 2 high energy electrons
  • The electrons are picked up by an electron acceptor and move along an ETC passing along electron carriers, releasing a small amount of energy used to produce ATP
  • The 2 electrons replace 2 electrons being released from PSI as it’s hit by light, and they are passed by the carriers down the ETC
  • Hydrogens from photolysis of water reduce NADP to NADPH2
  • Electrons from photolysis of water replace the 2 electrons lost from PSII
29
Q

What does cyclic photophosphorylation produce?

A

ATP, not NADPH2, so no sugars can be made and no growth or respiration of roots, but allows maintenance

30
Q

What is required for the light independent reaction to occur?

A

ATP and NADPH2 from light dependent reaction

31
Q

What are limiting factors of the light independent reaction?

A
  • Temperature, as it’s controlled by enzymes
  • CO2 conc
  • ATP and NADPH2
  • Light intensity limits light dependent reaction, so limits production of ATP and NADPH2, and so limits the light independent reaction
32
Q

How is ATP produced in the light dependent reaction?

A
  • As electrons pass along the ETC of carriers from PSII to PSI, they provide enough energy to pump H+ ions from stroma across thylakoid membrane into thylakoid space
  • This sets up an electrochemical and a concentration gradient, as there are more H+ ions inside thylakoid membrane space than in stroma
  • H+ ions diffuse across thylakoid membrane through protein channels with ATP synthase, which produces ATP from ADP + Pi
33
Q

What happens in the light independent reaction? (Calvin cycle)

A
  • Rubisco catalyses the reaction between CO2 and RuBP forming an unstable 6C intermediate which breaks into 2 molecules of G3P
  • 2 ATP molecules provide energy as they are converted into 2ADP+Pi
  • 2 NADPH2 molecules are oxidised, reducing GP into TP
34
Q

What does non-cyclic photophosphorylation produce?

A
  • O2, ATP and NADPH2, and allows sugars to be made
35
Q

Why does cyclic phosphorylation not allow growth?

A

Because the production of new sugars, cellulose, proteins etc needs the Calvin cycle, but that can’t occur without ATP as well as NADPH2, which cyclic phosphorylation doesn’t produce

36
Q

Why do plants die if they only undergo cyclic phosphorylation?

A
  • Cyclic phosphorylation doesn’t produce NADPH2 required for light independent reaction
  • Calvin cycle can’t occur so sugars aren’t produced
  • Plants die as the roots can’t respire without sugar
37
Q

What happens to 5 out of 6 TP molecules in the Calvin cycle?

A

They’re converted to 5C RuP, which is then phosphorylated by an ATP molecule forming RuBP

38
Q

What happens if O2 builds up in the chloroplast?

A
  • Rubisco is very vulnerable to O2, and the O2 can combine with RuBP on the active site and the cycle stops functioning
  • Therefore stomata of most plants must be wide open during the day
39
Q

How is the leaf adapted for gas exchange?

A
  • Large SA
  • Thin
  • Stomatal pores
  • Air spaces in spongy mesophyll
  • Spaces between palisade cells
40
Q

How are the leaf cells adapted for gas exchange?

A
  • Cuticle and epidermis are transparent; cellulose walls are thin
  • Palisade cells have a large vacuole
  • Palisade cells are cylindrical, elongated at right angles to the surface of the leaf
41
Q

How are the chloroplasts adapted for gas exchange?

A
  • Large SA
  • They move and rotate within palisade cells
  • Pigments in the thylakoids are in a single layer at the surface of the thylakoid membrane
  • 5x as many chloroplasts in palisade cells as in spongy mesophyll cells
42
Q

What does the correlation between the action spectrum and the absorption spectrum suggest?

A

That the pigments responsible for absorbing the light are used in photosynthesis

43
Q

How many proton pumps are there in the ETC of respiration and how many are there in photosynthesis?

A

Respiration - 3

Photosynthesis - 1

44
Q

Where does the photolysis of water occur?

A

In the thylakoid space

45
Q

How is the proton gradient maintained between the thylakoid space and the stroma?

A
  • The proton pump associated with the ETC pushes protons into the thylakoid space
  • The photolysis of water in the thylakoid space
  • The removal of protons from the stroma reducing NADP
46
Q

In Calvin’s lollipop apparatus, why was hot methanol used?

A

To denature the enzymes so that the products present at that time don’t continue to change

47
Q

In Calvin’s lollipop apparatus, why was radioactive carbon used?

A

It allows them to be identified

48
Q

In Calvin’s lollipop apparatus, why was a rapid action tap used?

A

As this allows many small samples to be collected over a short time

A LEVEL BIOLOGY (13 decks)

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