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Biology > 11. PHOTOSYNTHESIS > Flashcards

11. PHOTOSYNTHESIS Flashcards

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1
Q

Write a full and balanced photosynthesis symbol equation

A

6CO2 + 6H2O (+ light) → C6H12O6 + 602

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2
Q

Where does the energy for photosynthesis originate from?

A

Sunlight

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3
Q

Name five ways the glucose produced from photosynthesis is used

A

Respiration, stored as starch, converted into amino acids, cellulose and lipids

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4
Q

Name three parts of a plant that contains photosynthesising cells

A

Leaves, stems and branches

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5
Q

Describe the two adaptations of leaves that maximises light absorption

A

They have a large surface area and are arranged to minimise overlapping

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6
Q

Why are leaves thin?

A

To provide a short diffusion distance, and to ensure light can be absorbed in the first few μm (micrometer)

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7
Q

Why are the leaf cuticle and epidermis transparent?

A

To allow light to pass through to the photosynthetic palisade mesophyll tissue underneath

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8
Q

Why is the waxy cuticle waterproof?

A

To reduce the rate of transpiration from the top of the leaf

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9
Q

How is the palisade mesophyll tissue adapted for a maximum rate of photosynthesis?

A

The cells are tightly packed together, and the cells contain more chloroplasts

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10
Q

What is the function of stomata?

A

To allow gas exchange between the atmopshere and the inside of the leaf

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11
Q

What do the stomata open and close in response to?

A

Changing light intensity and changing temperature

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12
Q

How is the spongy mesophyll tissue adapted to its function?

A

It has air spaces between cells to allow gas exchange between the atmopshere and the palisade mesophyll tissue

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13
Q

Name the three photosynthetic pigments found in the chloroplast

A

Chlorophyll a, chlorophyll b and carotenoids (accessory pigments)

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14
Q

Which colours are absorbed by the photosynthetic pigments?

A

Violet, blue and red are absorbed

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15
Q

Which colours are reflected by the photosynthetic pigments?

A

Green, yellow and orange are reflected

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16
Q

Why do plants have more than one photosynthetic pigment?

A

To absorb a wider range of wavelengths of light

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17
Q

Name the two reactions that make up the process of photosynthesis

A

Light Dependent Reaction and Light Independent Reaction

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18
Q

Where does the LDR occur?

A

In the thylakoid membranes of the chloroplast (or grana)

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19
Q

What is the first stage in the LDR?

A

Photoionisation

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20
Q

Describe photoionisation

A

Chlorophyll absorbs light energy, which excites electrons. Two electrons leave the chlorophyll

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21
Q

What is the purpose of photolysis?

A

To replace the electrons lost from the chlorophyll in photoionisation

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22
Q

Write a full and balanced symbol equation for photolysis

A

H2O → 2H+ + 2e- + 1/2 O2

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23
Q

What happens to the O2 formed from photolysis?

A

It is used in respiration / diffuses out of the leaf as waste

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24
Q

What happens to the H+ formed from photolysis?

A

They bond with NADP+ and 2e- to make NADPH

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25
Q

Describe what happens to the excited electrons from photoionisation

A

They travel down the electron transport chain releasing energy

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26
Q

How is the energy used that is released from the excited electrons as they travel down the ETC?

A

It is used to pump H+ from the stroma into the thylakoid lumen

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27
Q

What does the pumping of the H+ from the stroma to the lumen create?

A

An electrochemical gradient over the thylakoid membrane

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28
Q

Describe chemiosmosis

A

H+ flow through ATP Synthase down an electrochemical gradient

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29
Q

Describe how chemiosmosis facilitates the production of ATP

A

The flow of H+ through ATP Synthase causes it to bond ADP and Pi to make ATP

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30
Q

What is phosphorylation?

A

The bonding of ADP and Pi to create ATP

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31
Q

Write an equation for the production of ATP by phosphorylation

A

ADP + Pi → ATP

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32
Q

Where is ATP Synthase found?

A

It is embedded in the thylakoid membranes at the end of the ETC

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33
Q

What is the final electron acceptor in the ETC?

A

NADP+

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34
Q

Describe how NADPH is produced in the LDR

A

Two electrons from the ETC bond with NADP+ and H+ to form NADPH

35
Q

What is a coenzyme?

A

A molecule that transports particles from one reaction to another

36
Q

Name the coenzyme used in photosynthesis

A

NADPH

37
Q

What happens to the NADPH and ATP produced from the LDR?

A

They are transported to the stroma where they are used in the LIR

38
Q

What are the reduced and oxidised versions of the NADP+/NADPH ?

A

Reduced version = NADPH
Oxidised version = NADP+

39
Q

Where does the LIR occur?

A

In the stroma

40
Q

Name the stages of the LIR

A

Carbon fixation, reduction and regeneration

41
Q

Apart from ATP and NADPH, name all the molecules involved in the LIR, and how many carbon atoms they contain

A

RuBP (5C)
CO2 (1C)
GP (3C)
Triose Phosphate (3C)
Glucose (6C)

42
Q

Describe what happens in the carbon fixation stage of the LIR

A

1 molecule of RUBP bonds with 1 molecule of CO2 (catalysed by rubisco) to form 2 molecules of GP

43
Q

Describe what happens in the reduction stage of the LIR

A

2 molecules of GP are reduced to 2 molecules of TP by 2 molecules of NADPH using energy released from 2 molecule of ATP

44
Q

How many carbon atoms from 2 molecules of Triose Phosphate are used to make glucose?

A

One

45
Q

Describe what happens in the regeneration stage of the LIR

A

Triose Phosphate is regenerated into 1 molecule of RuBP using the energy from 1 molecule of ATP

46
Q

How many turns of the calvin cycle does it take to produce one moelcule of glucose?

A

Six

47
Q

How many molecules of ATP and NADPH are used in one turn of the calvin cycle?

A

3 x ATP
2 x NADPH

48
Q

How many molecules of ATP and NADPH are used to form one molecule of glucose?

A

18 x ATP
12 x NADPH

49
Q

Name the three limiting factors of photosynthesis

A

Light intensity, temperature and carbon dioxide concentration

50
Q

Explain why increasing light intensity increases the rate of the light dependent reaction of photosynthesis?

A

It increases the light energy absorbed by the chlorophyll, which increases the number of electrons travelling down the ETC, which increases the NADPH & ATP formed.

51
Q

Explain why increasing light intensity increases the rate of the light independent reaction of photosynthesis?

A

It increases the NADPH & ATP formed in the LDR, which increases the glucose formed in the LIR

52
Q

Describe the relationship between light intensity and rate of photosynthesis when light is a limiting factor

A

It is directly proportional

53
Q

Why does the rate of photosynthesis fluctuate through a normal day?

A

Because the light intensity changes

54
Q

Describe how the rate of photosynthesis fluctuates through a normal day

A

The rate of photosynthesis will be zero at night, then increase as the sun rises in the morning. It will peak at the warmest and lightest part of the day (early afternoon), and reduce again to zero as the sun sets

55
Q

What is a plant’s compensation point?

A

The point at which the rate of photosynthesis and rate of respiration are the same

56
Q

When a plant is operating above its compensation point, which gas is there a net production of?

A

Oxygen

57
Q

When a plant is operating below its compensation point, which gas is there a net production of?

A

Carbon Dioxide

58
Q

Why is a plant not able to grow when it is operating below its compensation point?

A

Because there is no excess glucose for the plant to convert into amino acids for growth

59
Q

Describe three adaptations of shade-adapted plants

A

Lower respiratory losses (lower rate of respiration)
More chloroplasts per cell
More thylakoids per chloroplast

60
Q

Why does increasing temperature above a certain point cause the rate of photosynthesis to reduce to zero?

A

Because rubisco will become denatured, reducing the rate of carbon fixation to zero

61
Q

Describe the relationship between temperature and rate of photosynthesis when temperature is a limiting factor

A

It is directly proportional

62
Q

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

A

Because increasing temperature increases the rate of rubisco action

63
Q

Describe the stress response in plants

A

Stomata close to reduce the rate of transpiration. This can also reduce the rate of photosynthesis.

64
Q

What is photorespiration?

A

When oxygen binds to rubisco instead of carbon dioxide

65
Q

Name the two conditions under which photorespiration will occur

A

High temperatures
A low ratio of carbon dioxide to oxygen

66
Q

What are the effects of photorespiration?

A

Less GP, Triose Phosphate and sugars are made.
RuBP also takes longer to regenerate.

67
Q

Name two ways farmers and food producers maintain optimum conditions to maximise the rate of photosynthesis in their crops

A

They will maintain the optimum temperature for rubisco action
They will increase the ratio of carbon dioxide to oxygen

68
Q

Describe the relationship between carbon dioxide concentration and rate of photosynthesis when carbon dioxide concentration is a limiting factor

A

It is directly proportional

69
Q

Why is carbon dioxide concentration most likely to be the limiting factor in nature?

A

The optimum carbon dioxide concentration for photosynthesis is 1%, however the carbon dioxide concentration in the atmosphere is ~0.04%

70
Q

Why would increasing carbon dioxide concentration increase the rate of photosynthesis?

A

The rate of carbon fixation would increase, which would increase the rate of sugars made in the LIR

71
Q

When carbon dioxide concentration is not limiting, why are the levels of GP and RuBP constant?

A

GP and RuBP are being formed at the same rate as they are being used

72
Q

When carbon dioxide concentration is not limiting, why is there twice as much GP as RuBP?

A

Because one molecule of RuBP binds with CO2 to make two molecules of GP

73
Q

When carbon dioxide becomes a limiting factor, why does the amount of RuBP increase?

A

There is less CO2 to bind with RuBP in carbon fixation, therefore less RuBP is converted into GP

74
Q

When carbon dioxide becomes a limiting factor, why does the amount of GP decrease?

A

There is less CO2 to bind with RuBP in carbon fixation, therefore less RuBP is converted into GP

75
Q

Name the two forms of DCPIP, and their colours

A

Oxidised form = blue
Reduced form = colourless

76
Q

What is DCPIP used to indicate in plants?

A

The presence of the LDR (by indicating the presence of electrons)

77
Q

Where are the electrons coming from that are accepted by DCPIP?

A

The electron transport chain

78
Q

How would altering the volume of DCPIP used alter the time it took to decolourise?

A

The higher the volume, the longer the time it would take to decolourise

79
Q

Why were the leaves blended before being used in the DCPIP experiment?

A

To release the chloroplasts from the cells

80
Q

Why is it important not to overblend the leaves in the DCPIP experiment?

A

So as not to damage the chloroplasts

81
Q

Why does the isolating medium need to be ice cold in the DCPIP experiment?

A

To reduce enzyme activity as much as possible before the experiment begins to reduce the amount of photosynthesis prior to the experimental period

82
Q

What are the two experimental proxies we use to measure the rate of photosynthesis?

A

Oxygen produced and carbon dioxide uptake

83
Q

Which experimental proxy for photosynthesis is most useful when measuring the rate of the LDR?

A

Oxygen produced

84
Q

Which experimental proxy for photosynthesis is most useful when measuring the rate of the LIR?

A

Carbon dioxide uptake

Biology (26 decks)

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