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A Level Biology OCR > 5.6 Photosynthesis > Flashcards

5.6 Photosynthesis Flashcards

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1
Q

What is carbon fixation?

A

The process by which CO2 is fixed into organic compounds, and regulates the amount of CO2 in the atmosphere.

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2
Q

Photosynthesis is ________.

A

Endothermic

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3
Q

What is the compensation point?

A

When photosynthesis and respiration take place at the same rate, no net change in amount of carbohydrate.

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4
Q

What is a compensation period?

A

The amount of time it takes a plant to reach its compensation point.

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5
Q

Where does the light dependant stage take place?

A

Thylakoid membrane

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6
Q

What is a photosynthetic pigment?

A

Pigment that absorbs specific wavelengths of light and trap their energy.

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7
Q

What are examples of photosynthetic pigments?

A

Chlorophyll a, Chlorophyll b, carotene

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8
Q

Where does the light independant stage take place?

A

Stroma

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9
Q

What is the stroma?

A

Fluid filled matrix in the chloroplasts

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10
Q

What is a granum?

A

Stack of thylakoid membranes

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11
Q

What is a thylakoid?

A

Flattened membrane bound sac found in chloroplasts, contains photosystems and photosynthetic pigments.

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12
Q

Where are photosystems found?

A

Thylakoid membranes

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13
Q

Why do granum have such a high surface area?

A

Space for more photosystems and photosynthetic pigments, and electron carriers and ATP Synthase

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14
Q

What is a coenzyme?

A

Molecule that aids the function of an enzyme, by transferring a group from one molecule to another

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15
Q

What are the two types of photosynthetic pigments in photosystems?

A

Primary pigments and accessory pigments.

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16
Q

What do primary photosynthetic pigments do?

A

They are reaction centres where electrons are excited in the light dependant reaction.

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17
Q

What do accessory photosynthetic pigments do?

A

They are light harvesting systems surrounding reaction centres, transferring light energy to them to increase electron excitement.

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18
Q

What wavelength of light is best absorbed by PSI?

A

700nm

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19
Q

What wavelength of light is best absorbed by PSII?

A

680nm

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20
Q

Chloroplasts contain their own ____ and _____.

A

DNA and small ribosomes.

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21
Q

What happens to carbohydrates that are made but not used in chloroplasts?

A

Stored as starch grains in stroma.

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22
Q

How is ATP made in the light dependant reaction?

A

Photophosphorylation

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23
Q

What is photolysis?

A

Using light energy to split water into protons, electrons and oxygen

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24
Q

When does photolysis occur?

A

The light dependant reaction

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25
Q

When does cyclic and non-cyclic photophosphorylation occur?

A

Light dependant reaction

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26
Q

What are the products of non-cyclic photophosphorylation?

A

ATP, NADPH, O2

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27
Q

What links photosystems in thylakoid membranes?

A

Electron carriers

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28
Q

What are electron carriers?

A

Proteins that transfer electrons

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29
Q

What is an electron transport chain?

A

A chain of proteins through which excited electrons flow

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30
Q

What makes up the electron transport chain in non-cyclic photophosphorylation?

A

The electron carriers and the photosystems

31
Q

What is the first step of non-cyclic photophosphorylation?

A

Light energy is absorbed by PSII, exciting electrons in chlorophyll until they move down the electron transport chain to PSI

32
Q

What is the second step of non-cyclic photophosphorylation?

A

Photolysis of water to replace the electrons lost from PSII.

33
Q

What is chemiosmosis?

A

The process of electrons flowing down an electron transport chain to provide energy to pump protons creating a proton gradient to drive ATP synthesis

34
Q

What is the third step of non-cyclic photophosphorylation?

A

Energy from excited electrons moving along an electron transport chain is used to pump protons into thylakoid creating a conc gradient, then making ATP by chemiosmosis

35
Q

What is the fourth and final step of non-cyclic photophosphorylation?

A

Light energy excites electrons in PSI, then they are transferred to NADP with a proton to make NADPH

36
Q

What can be used to separate photosynthetic pigments?

A

Thin layer chromatography

37
Q

What photosystem is used in cyclic photophosphorylation?

A

Only PS1

38
Q

What happens in cyclic photophosphorylation?

A

e- from chlorophyll are passed back to PS1, and repeatedly flow through PS1, only making a small amount of ATP

39
Q

What are the products of cyclic photophosphorylation?

A

Small amounts of ATP

40
Q

When does CO2 fixation take place?

A

Calvin cycle / light independant reaction

41
Q

What makes up a photosystem?

A

Membrane protein and photosynthetic pigments

42
Q

How does the light independant reaction rely on the light dependant reaction?

A

ATP and NADPH are required to keep it going, which are made in the light dependant reaction

43
Q

What does RuBisCO catalyse?

A

RuBP + CO2 > 2GP

44
Q

What is the order of the Calvin cycle?

A

RuBP > GP > TP > RuBP

45
Q

What are the uses of TP?

A

As a starting material for synthesis of carbs, lipids and proteins

46
Q

How many turns of the Calvin cycle are needed to make 1 hexose sugar (glucose) ?

A

6 turns

47
Q

How is RuBP regenerated?

A

5 out of 6 TPs made are used to regenerate RuBP

48
Q

How many of each light dependant reaction product are needed to make 1 glucose?

A

18 ATP and 12 NADPH

49
Q

What is needed to go from GP to TP?

A

2ATP and 2NADPH

50
Q

What is used to go from TP back to RuBP?

A

1ATP

51
Q

What makes GP?

A

RuBP + CO2 > GP

52
Q

What is chemiosmosis?

A

The process of e- flowing down an e- transport chain to create a H+ gradient across a membrane to drive ATP synthesis

53
Q

What is the role of water in photosynthesis?

A

Photolysis of water makes electrons, H+ and O2 gas. The e- are used to replace the excited ones lost from chlorophyll

54
Q

What is the effect of intense light on the Calvin cycle?

A

High levels of RuBP and TP, low levels of GP

55
Q

What is the effect of dim light on the Calvin cycle?

A

Low levels of RuBP and TP and high levels of GP as it cannot be reduced to TP without the LDR

56
Q

What is the effect of low CO2 concentration on the Calvin cycle?

A

RuBP accumulates as it can’t accept CO2, and GP and TP cannot be made

57
Q

What is the effect of high CO2 concentration on the Calvin cycle?

A

Low amount of RuBP as it is combined with CO2, high levels of GP and TP

58
Q

What is a limiting factor of photosynthesis?

A

The factor which is at its least favourable level will limit photosynthesis rate, even when the other factors are at the most favourible.

59
Q

What factors affect rate of photosynthesis?

A

Light intensity, Carbon dioxide concentration, and Temperature

60
Q

How does light intensity affect photosynthesis rate?

A

Light of blue-red wavelength is used in photosynthesis, so as you increase the intensity the rate increases.

61
Q

How does CO2 concentration affect photosynthesis rate?

A

Increasing CO2 concentration increases photosynthesis rate, but not too high as this causes stomatal closure.

62
Q

How does temperature affect photosynthesis rate?

A

Photosynthesis rate is highest when temp is at around 30C. Too high/too low and the rate decreases

63
Q

What does ATP Synthase do?

A

An enzyme that aids H+ moving down their concentration gradient back to the stroma, and the energy from this movement makes ATP from ADP +Pi

64
Q

What happens to stomata at high temperatures and how does this affect photosynthesis?

A

They close to avoid losing water, stopping CO2 from entering the leaf and decreasing photosynthesis rate

65
Q

What happens to thylakoid membranes under high temperatures?

A

May become damaged and reduce rate of LDR by reducing electron transfer via electron carriers

66
Q

What happens to the chloroplasts outer membrane when at high temp?

A

They become damaged and cause enzymes such as RuBP to be released into cell, reducing LIR

67
Q

What happens to chlorophyll at high temp?

A

Could become damaged and reduce amount of pigment that can absorb light energy, reducing LDR

68
Q

What is the saturation point?

A

Where a factor is no longer limiting the reaction, and something else is

69
Q

What happens to the Calvin cycle at extreme temperatures?

A

RuBP, GP and TP levels will all fall because the enzymes used to make them will either be denatured or inactive.

70
Q

What is water stress?

A

When a plant has insufficient water to supply itself and the transpiration stream

71
Q

What affect does water stress have on photosynthesis?

A

Decreases rapidly as leaves wilt and stomata close due to cells becoming plasmolysed and tissues becoming flaccid.

72
Q

What causes stomatal closure?

A

Abscisic acid release in times of water stress

73
Q

How do you measure the rate of photosynthesis?

A

Measure the rate of uptake of raw material e.g. CO2 or the rate of production of product, O2

74
Q

How does a photosynthometer work?

A

It is an airtight apparatus that measures the volume of O2 produced by a plant, by measuring the length of an air bubble in a capillary tube

A Level Biology OCR (28 decks)

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