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Biology 6th Form OCR A (missing exchange systems) > Module 5: Energy for biological processes (Photosynthesis) > Flashcards

Module 5: Energy for biological processes (Photosynthesis) Flashcards

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1
Q

Compensation Point:

A

The volume of oxygen produced is equal to the volume used for aerobic respiration.

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2
Q

What is meant by photosynthesis and aerobic respiration being complementary reactions?

A

Products of photosynthesis are the reactants of aerobic respiration vice versa.

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3
Q

Producers:

A

Photoautotrophs use photosynthesis and cell respiration. Source of biomass for food web

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4
Q

Consumers:

A

Heterotrophs, undertake cell respiration and ingest/absorb photosynthetic products.

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5
Q

Photosynthesis: Type of process

A

Anabolic process

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6
Q

Cell respiration: type of process

A

Catabolic process

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7
Q

Photosynthesis: Summary

A

Water is broken down into oxygen to release electrons for an electron transport chain. Electrons from the transport chain are taken up by hydrogen carriers. ATP is synthesised through chemiosmosis. Uses Calvin cycle to synthesise glucose.

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8
Q

What is the name of the cycle used to synthesise glucose:

A

Calvin Cycle

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9
Q

Is photosynthesis endothermic or exothermic?

A

Endothermic

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10
Q

Is cell respiration endothermic or exothermic?

A

endo -Use of Krebs of cycle to break down glucose
endo - Hydrogen carriers to release electrons for an electron transport chain
exo -Electrons from transport chain taken up by oxygen to form water.
exo -Hydrolysis of ATP

(overall exothermic)

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11
Q

Similarity between Respiration and photosynthesis:

ATP PRODUCTION

A

Both produce ATP - In photosynthesis ATP is produced via transducing light energy (photophosphorylation) and used to make organic molecules.

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12
Q

Similarity between Respiration and photosynthesis:

Electron transport chain

A

Production of ATP involves an electron transport chain and chemiosmosis in both.

  • photosynthesis- electrons are donated by chlorophyll and protons accumulate in the thylakoid lumen
  • Cell Respiration - electrons are donated by hydrogen carriers and protons accumulate in the intermembrane space
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13
Q

What is the stroma?

A

The central cavity that contains appropriate enzymes and suitable pH for the Calvin cycle to occur

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14
Q

What is a thylakoid?:

A

Flattened discs that have a small internal volume to maximise hydrogen gradient upon proton accumulation. ETC and ATP synthase for phosphorylation. Location of the light dependent phase of photosynthesis.

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15
Q

What is the grana:

A

Thylakoids are arranged into stacks to increase SA;Vol ratio of the thylakoid membrane.

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16
Q

What are photosystems:

A

Pigments organised into photosystems in the thylakoid membrane to maximise light absorption.

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17
Q

What are the lamellae

A

Connects and separates thylakoid stacks, maximising photosynthetic efficiency.

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18
Q

What is located in the stroma?

A

Starch, lipid, ribosomes, chloroplast DNA.

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19
Q

Where are chlorophyll pigments located?

A

They are sandwiched within lipids and proteins in thylakoid membranes.

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20
Q

What molecules are with the pigments:

A

Enzymes and electron-carrier molecules.

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21
Q

Which pigment is a primary pigment:

A

Chlorophyll a

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22
Q

What do antennae pigments do?

A

Funnel energy to primary pigments to excite electrons.

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23
Q

Absorption Spectrum:

A

Wavelengths absorped by each pigment

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24
Q

Action spectrum:

A

Overall rate of photosynthesis at each wavelength.

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25
Q

What is a pigment made up of?

A

Chlorin ring and hydrocarbon tail.

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26
Q

Chlorin ring:

A

light reacting component (magnesium centre) of chlorophyll

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27
Q

Purpose of hydrocarbon tail in pigment?

A

Anchors chlorophyll molecule to thylakoid centre.

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28
Q

Photosystem:

A

Light harvesting system that absorbs and funnels energy to a primary pigment to excite a delocalised electron which is transferred to an electron acceptor molecule.

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29
Q

Role of chlorophyll a:

A

Excite and release an delocalised electron

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30
Q

What do electron acceptors do in a photosystem?

A

Synthesise ATP

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31
Q

How can photosystems be differentiated?

A

By the wavelength of light absorbed at the photosystem’s primary pigment.

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32
Q

What is chemiosmosis?

A

The movement of ions across a partially permeable membrane down their electrochemical gradient.

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33
Q

What is the purpose of proton pumps in chemiosmosis?

A

To create an electrochemical gradient through the active transport of protons across the thylakoid membrane.

34
Q

What is the purpose of accessory pigments?

A

To form a light harvesting system which absorbs light energy which is funnelled to the primary pigment, releasing high energy electrons.

35
Q

What are the components of a light harvesting system?

A

The light harvesting system and the reaction centre

36
Q

What is the effect of proton pumps on the location of protons in chemiosmosis?

A

There are more protons inside the thylakoid than the stroma, creating an electrochemical gradient.

37
Q

Why is the electrochemical gradient important in chemiosmosis? (photosynthesis)

A

Allows the protons to diffuse out of the thylakoid space into the stroma through ATP synthase embedded in the thylakoid membrane.

38
Q

Where is the light dependent stage of photosynthesis located?

A

The thylakoid membranes.

39
Q

What is the purpose of a photosystem in photosynthesis?

A

To excite an electron and pass it through an electron transport chain to synthesise ATP through chemiosmosis.

40
Q

What is meant by ATP releasing energy in a coupled reaction?

A

Energy is initially released through the hydrolysis of ATP by ATPase and then energy is used during phosphorylation.

41
Q

How do electrons get excited?

A

Electrons absorb light energy, released when chemical bonds are broken, pass into electron transport chain to form a proton gradient.

42
Q

Electron Transport Chain: Waterfall Model

A

Electrons pass from carrier to carrier have a progressively lower energy level.
Energy released.
Pump protons gradient
Maintained by an impermeability to H+
Protons must move through hydrophilic membrane channels linked to ATP synthase.
Providing energy to resynthesise ATP from ADP and Pi.

43
Q

Photophosphorylation via Chemiosmosis:

A

The use of light energy from photosynthesis is used to establish a proton gradient to phosphorylate ADP into ATP.

44
Q

What are the two hydrogen carrier macromolecules:

A

NAD and NADP

45
Q

What do NAD and NADP carry?

A

Hydride ions

46
Q

What are hydrogen carriers?

A

Organic macromolecules that transport hydrogen atoms from one place to another for use in metabolic processes.

47
Q

What type of photophosphorylation only uses photosystem 1?

A

Cyclic- photophosphorylation

48
Q

What type of photophosphorylation uses both photosystems 1&2:

A

Noncyclic- photophosphorylation

49
Q

What is the main function of the light dependent phase?

A

To use light and photosynthetic pigments to release ATP and reduce NADP to supply the Calvin cycle.

50
Q

What is the light dependent phase:

A

The use of photosynthetic pigments to convert light energy into chemical energy.

51
Q

What are the key stages of the light dependent stage?

A

Excitation of photosystems by light energy
Production of ATP by chemiosmosis
Reduction of NADP

52
Q

Where does photolysis take place:

A

An enzyme bound to photosystem 2

53
Q

What are the products of photolysis and what are they used for?

A

2H+ Reduces NADP into NADPH
e- Replace electrons lost by PS2
1/2 O2 By-product

54
Q

What is the name of the system excited electrons travel through in the thylakoid membrane from PS2 to PS1 across proton pumps?

A

An electron transport chain

55
Q

What is photophosphorylation?

A

The production of ATP using light as the initial energy source.

56
Q

Where do electrons released by PS2 go once they are deenergised after an electron transport chain?

A

PS1

57
Q

What are the 3 factors affecting the rate of photosynthesis?

A

Temperature, CO2 concentration and light intensity.

58
Q

How does light intensity affect the rate of photosynthesis?

A

Light is utilised in the photolysis of water to allow for chemiosmosis through non-cyclic photophosphorylation. Light is also used for the excitation of electrons in photosystems.

59
Q

Why is light intensity a necessary factor?

A

Light is required to produce ATP and NADPH which is required for the reduction of GP and regeneration of RuBP.

60
Q

What is the effect of light intensity being limited?

A

Less light dependent reaction -> less ATP and NADPH -> less reduction of GP and regeneration of RuBP -> build up of GP

61
Q

How does CO2 concentration affect the rate of photosynthesis?

A

The CO2 provides a source of carbon for fixation in the Calvin Cycle.

62
Q

Why is CO2 a necessary factor?

A

Carbon fixation is dependent on CO2 and-so is required for TP synthesis.

63
Q

What is the effect of CO2 concentration being limited?

A

Reduced carbon fixation -> less GP -> Less TP -> Less glucose produced
Reduced Carbon fixation -> buildup of RuBP

64
Q

How does temperature affect the rate of photosynthesis?

A

The temperature affects enzyme controlled reactions e.g carbon fixation and photolysis.
Photorespiration occurs at higher temperature due to build-up of O2 in leaves -> reduces photosynthetic efficiency.

65
Q

Why is temperature a necessary factor?

A
  • Achieving the activation energy for reaction
  • Freq. of successful collisions.
  • Enzyme Action -> increases rate significantly
  • Photorespiration -> reduces photosynthetic efficiency.
66
Q

What is the effect of temperature being limiting?

A

Either:
Less kinetic energy -> fewer successful collisions.
Too high kinetic energy -> denaturing of enzymes -> change in shape of active site -> prevents reaction.
+-> Photorespiration

67
Q

How many CO2 molecules are required to form 1/2 a glucose molecule?

A

3 molecules

68
Q

How many carbons are in GP?

A

3 carbons

69
Q

How many GP molecules are required to form 1/2 a glucose molecule?

A

6 molecules

70
Q

How many carbons are within a TP molecule?

A

3 carbons

71
Q

How many molecules of TP leave the cycle to form 1/2 glucose?

A

1 molecule

72
Q

Which parts of the Calvin Cycle require ATP?

A

The reduction of GP into TP, using 6ATP and 6NADPH#

The regeneration of RuBP using 3 ATP

73
Q

How many TP molecules are used to regenerate 3 RuBP molecules?

A

5

74
Q

How many carbons are within RuBP?

A

5

75
Q

What is a limiting factor?

A

A required factor in short supply.

76
Q

What molecule competitively inhibits Rubisco?

A

O2

77
Q

Photorespiration (IN DEPTH):

A

Occurs at high and dry temperatures -> stomata close. CO2 conc. decreases + O2 conc. increases
O2 competitively inhibits rubisco and produces products that can’t produce sugars. -> decreases efficiency of Calvin cycle and reduces the energy yield.

78
Q

What is the enzyme that catalyses the fixation of CO2 to RuBP?

A

Rubisco

79
Q

What are the two direct methods of measuring photosynthesis?

A

Measure uptake of carbon dioxide in a unit time

Measure production of oxygen in a unit time

80
Q

What is an indirect method of measuring photosynthesis?

A

Change in biomass in a unit time - dry mass per year

81
Q

What is the hydrogen carrier in photosynthesis?

A

NADP

82
Q

What is NADP reduced into?

A

NADPH

Biology 6th Form OCR A (missing exchange systems) (27 decks)

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