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OCR A level biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Describe why autotrophs are important to life

A
  • autotrophs undergo photosynthesis
  • this produces biomass
  • provides direct food source for consumers
  • provides food source for the food source of consumers
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2
Q

Why does photosynthesis require energy from the sun whilst respiration does not?

A

The energy required to break bonds in small organic molecules is greater than the energy released from the formation of organic molecules.

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3
Q

Why does respiration not require sunlight whilst photosynthesis does?

A

Total energy required to break all bonds in complex organic molecules is less than the total energy released in the formation of all bonds in the smaller organic products. Excess energy released by the formation of the bonds used to synthesise ATP.

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4
Q

What is the overall equation for photosynthesis?

A

6H2O + 6CO2 —> C6H12O6 + 6O2

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5
Q

What is a stack of thylakoid membranes called?

A

Granum

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6
Q

What connects the granum in a chloroplast?

A

Lamellae

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7
Q

What are the two stages of photosynthesis?

A

The light dependent and light independent stages

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8
Q

Where do the light dependent stages of photosynthesis occur?

A

On thylakoid membranes in chloroplasts

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9
Q

Where do the light independent reactions of photosynthesis occur?

A

In the stroma of chloroplasts

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10
Q

What is another name for the light independent reactions?

A

The Calvin cycle

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11
Q

Define photosynthetic pigment

A

Substances which absorb light energy and convert it into chemical energy. Different photosynthetic pigments absorb different wavelengths of light energy

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12
Q

In which part of photosynthesis are photosynthetic pigments used?

A

Light dependent reactions

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13
Q

Define light harvesting system

A

A group of protein and chlorophyll molecules found in the thylakoid membranes of the chloroplasts in a plant cell

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14
Q

Define reaction centre

A

A complex of proteins and chlorophyll a which undergoes the primary energy conversion of photosynthesis

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15
Q

Define photosystem

A

Protein complexes involved in the absorption of light and electron transfers in photosynthesis

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16
Q

Which pigment is found the the reaction centres of photosystems?

A

Chlorophyll a

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17
Q

What is the primary pigment in photosynthesis?

A

Chlorophyll a

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18
Q

What are antennae pigments?

A

Photosynthetic pigments other than chlorophyll a

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19
Q

What is the function of antennae pigments?

A

They absorb different wavelengths of light to chlorophyll a, and channel this light energy to the reaction centres.

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20
Q

Give 3 examples of antennae pigments

A

Chlorophyll b
Xanthophylls
Carotenes

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21
Q

What is the purpose of having different photosynthetic pigments in chloroplasts absorbing different wavelengths?

A
  • allows a wider range of wavelengths of light to be absorbed
  • more light energy therefore can be absorbed makes photosynthesis more efficient
  • ensures pigments don’t compete for same wavelength
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22
Q

Explain how a large number of thylakoids/grana in a chloroplast adapt chloroplasts for photosynthesis

A
  • provides large surface area for the light dependent stage to occur on
  • ensures plenty of ATP and reduced NADP is provided for the light independent stage
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23
Q

Explain how the presence of stroma surrounding thylakoid membranes adapts chloroplasts for photosynthesis

A
  • allows products of light dependent reaction to pass efficiently from the thylakoid membranes to the stroma
  • stroma is the site of light independent reaction, which requires the products of the light dependent reaction
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24
Q

Explain how the presence of a double membrane separated by intermembrane space adapts chloroplasts for photosynthesis

A

It allows a proton gradient to be formed between the stroma and intermembrane space

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25
Q

What are the useful products of the light dependent reaction?

A

Reduced NADP

ATP

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26
Q

What is the waste product of the light dependent reaction?

A

O2

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27
Q

What is phosphorylation?

A

The addition of a phosphate group to a molecule

28
Q

Define photophosphorylation

A

The addition of an inorganic phosphate group using light energy, in the context of photosynthesis this is the addition of Pi to ADP to form ATP

29
Q

Define cyclic photophosphorylation

A

When the electron which stabilises the cholorphyll molecule on photosystem 1 is the same as the electron which was boosted to a higher energy level (Synthesis of ATP involving only photosystem 1)

30
Q

Define non-cyclic photophosphorylation

A

When the electron which stabilises the chlorophyll is different to the electron which was boosted to a higher energy level (synthesis of ATP and reduced NADP involving photosystems 1 and 2)

31
Q

Give the equation for photolysis

A

H2O —> 2H+ + 2e- + 1/2 O2

32
Q

In the context of photosynthesis what is photolysis?

A

The splitting of water using light energy

33
Q

Where does photolysis occur?

A

On the Oxygen evolving complex on photosystem 2

34
Q

What are the electrons from photolysis used for?

A

To stabilise the chlorophyll in photosystem 2.

35
Q

What happens when a photosystem absorbs light energy?

A
  • the light energy is transferred to the chlorophyll a in the reaction centre
  • due to the energy, an electron is excited and boosted to a higher energy level
36
Q

Does photolysis occur in cyclic or non-cyclic photophosphorylation?

A

Non-cyclic

37
Q

Outline what happens to an excited electron from chlorophyll a in cyclic photophosphorylation

A
  • passed through a series of electron carriers

- returned to the chlorophyll a to stabilise it

38
Q

What happens as a result of energy being released by electrons returning to their original energy level?

A
  • this is used to pump protons across the thylakoid membrane from the stroma into the thylakoid space
  • causing a proton gradient to be built up
39
Q

What happens when protons diffuse through ATP synthase?

A

ADP and Pi are synthesised into ATP

40
Q

Which photosystem(s) are involved in cyclic photophosphorylation?

A

Photosystem 1

41
Q

Which photosystem(s) are involved in non-cyclic photophosphorylation?

A

Photosystem 1 and 2

42
Q

Name the 2 enzymes involved in the light dependent reactions

A

ATP synthase

NADP reductase

43
Q

Outline the movement of an electron from chlorophyll a in photosystem 2

A
  • an electron in chlorophyll a in photosystem 2 is excited by light energy and boosted to a higher energy level
  • excited electron is transferred through a series of electron carriers to the chlorophyll a in photosystem 1
  • the electron is boosted again and transferred to NADP reductase
44
Q

What happens to the protons from photolysis?

A

They diffuse through ATP synthase back to the stroma, allowing ADP and Pi to be synthesised to ATP

45
Q

How is NADP reduced in non-cyclic photophosphorylation?

A

By the enzyme NADP reductase using H+ from ATP synthase and e- from chlorophyll

46
Q

Which products from the light dependent reactions are used in the Calvin cycle?

A

Reduced NADP

ATP

47
Q

Name the enzyme involved in the Calvin cycle

48
Q

What techniques did Melvin Calvin use to work out the Calvin cycle?

A
  • radiolabelling
  • 2 way chromatography
  • autoradiography
49
Q

What does RuBP stand for?

A

Ribulose Bisphosphate

50
Q

What does GP stand for?

A

Glycerate-3-phosphate

51
Q

What does TP stand for?

A

Triose phosphate

52
Q

What does ATP stand for?

A

Adenosine triphosphate

53
Q

What are the 2 roles of ATP in the Calvin cycle?

A
  • to release energy

- to donate Pi

54
Q

What reaction does RuBisCo catalyse?

A

The fixation of CO2 using RuBP

55
Q

How many Carbons does RuBP contain?

56
Q

How many phosphates does RuBP contain?

57
Q

Outline the order of compounds produced in the Calvin cycle starting with RuBP

A

RuBP
2 x GP
2 x TP
RuBP

58
Q

How many molecules of GP are made from one molecule of RuBP?

59
Q

How many carbons does GP contain?

60
Q

How many carbons does TP contain?

61
Q

How many phosphates does GP contain?

62
Q

How many phosphates does TP contain?

63
Q

What % of TP is regenerated into RuBP?

64
Q

What are the uses of TP?

A
  • TP can be converted into amino acids, lipids, and carbohydrates
  • TP is used to regenerate RuBP, ensuring the cycle continues
65
Q

Name two polysaccharides needed by plants

A

Starch

Cellulose

66
Q

Name two monosaccharides needed by plants

A

Glucose

Fructose

67
Q

What is photorespiration?

A

The process by which O2 is taken in to release CO2 and energy, using light energy

OCR A level biology (44 decks)

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