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AQA A Level Biology Paper 2 > Topic 5.1 - Photosynthesis > Flashcards

Topic 5.1 - Photosynthesis Flashcards

1
Q

Describe how ATP is synthesised

A

ATP is synthesised via condensation reaction between ADP and inorganic phosphate using energy from an energy-releasing reaction

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2
Q

What enzyme catalyses ATP synthesis?

A

ATP synthase

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3
Q

Where is the energy stored in ATP?

A

Energy is stored as chemical energy in the phosphate bond

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4
Q

What happens when ATP arrives (via diffusion) to a part of cell that needs energy?

A
  • ATP is hydrolysed back into ADP and inorganic phosphate
  • Chemical energy is released from phosphate bond and used by cell
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5
Q

What enzyme catalyses ATP hydrolysis?

A

ATP hydrolase

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6
Q

Draw an ATP molecule

A
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7
Q

Name and explain 6 properties that ATP has that makes it a good energy source

A
  • Stores or releases only a small, manageable amount of energy at a time- therefore no energy is wasted as heat
  • It’s a small, soluble molecule so it can be easily transported
  • (Easily) broken down in 1 step so energy can easily released instantaneously
  • It can be quickly re-made
  • Can make other molecules more reactive by transferring one of its phosphate groups to them (phosphorylation)
  • ATP can’t pass out of cell so cells always have immediate supply of energy
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8
Q

Define a metabolic pathway

A

Series of small reactions controlled by enzymes

e.g. respiration and photosynthesis

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9
Q

Define Phosphorylation

A

Adding phosphate to a molecule

e.g. ADP → ATP

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10
Q

Define Photolysis

A

Splitting (lysis) of a molecule using light (photo) energy

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11
Q

Define Photophosphorylation

A

Adding phosphate to a molecule using light

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12
Q

Define Photoionisation

A
  • When light energy excites electrons in an atom
  • Giving them more energy and causing them to be released
  • Release causes atom to become positively-charged ion
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13
Q

Define Hydrolysis

A

Splitting (lysis) of a molecule using water (hydro)

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14
Q

Define Decarboxylation

A

Removal of carbon dioxide from a molecule

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15
Q

Define Dehydrogenation

A

Removal of hydrogen from molecule

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16
Q

What do chloroplasts contain?

A

Photosynthetic pigments e.g. chlorophyll

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17
Q

What are photosynthetic pigments (e.g. chlorophyll a, chlorophyll b and carotene)?

A

Coloured substances that absorb light energy

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18
Q

Where are pigments found?

A

Thylakoid membranes = attached to proteins

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19
Q

What is a photosystem?

A

Protein + pigment

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20
Q

Name the 2 photosystems used by plants to capture light energy

A
  • Photosystem I (PSI)
  • Photosystem II (PSII)
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21
Q

What are carbohydrates that are produced by photosynthesis and not used straight away stored as and where?

A

As starch grains in the stroma

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22
Q

Where does the the light-dependent reaction occur?

A

Takes place in thylakoid membranes

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23
Q

Photosystems are linked by _____ ____

A

electron carriers

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24
Q

What are electron carriers?

A

Proteins that transfer electrons

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25
Q

Photosystems and electron carriers form an ____ ______ ____

A

electron transport chain

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26
Q

What is an electron transport chain?

A

Chain of proteins through which excited electrons flow

27
Q

Light-dependent reaction includes 2 types of photophosphorylation. Name them.

A
  • Non-cyclic Photophosphorylation
  • Cyclic Photophosphorylation
28
Q

Name the 4 main stages in the light-dependent reaction (non-cyclic photophosphorylation).

A
  1. Light energy excites electrons in chlorophyll
  2. Photolysis
  3. Energy from excited electrons make ATP…
  4. … and generates reduced NADP
29
Q

The Light-dependent Reaction

Describe Stage 1

A
  1. Chlorophyll (PSII) absorbs light
  2. Light energy excites electrons in chlorophyll
    • Electrons move to higher energy level
  3. High-energy electrons are released from chlorophyll and move down electrons transport chain to PSI
30
Q

The Light-dependent Reaction

Describe Stage 2

A
  1. Light energy splits water into protons (H+ ions), electrons & oxygen = photolysis
  2. Electrons used to replace electrons that passed out of chlorophyll along electron carriers
31
Q

The Light-dependent Reaction

Describe Stage 3

A
  1. Excited electrons lose energy as they move down electron transport chain
  2. Energy lost = used to pump H+ ions into thylakoid space, creating proton gradient
  3. Protons can now diffuse back into stroma via enzyme ATP synthase
    • Catalysed by ATP synthase
  4. Energy from movement combines ADP and P¡ to form ATP
32
Q

The Light-dependent Reaction

Describe Stage 4

A
  1. (Light energy is absorbed by PSI which excites electrons to even higher energy level)
  2. Electrons + protons (from stroma) are transferred to NADP = combine to reduce NADP to reduced NADP
34
Q

The Light-dependent Reaction

Describes what happen in cyclic photophosphorylation

A
  • ‘Cyclic’ ∵ electrons from chlorophyll molecule aren’t passed onto NADP
  • But passed back to PSI via electrons carriers
  • ∴ electrons are recycled
38
Q

What is chemiosmosis/the chemiosmotic theory?

A

The process of electrons flowing down electrons transport chain & creating a proton gradient across the membrane to drive ATP synthesis

40
Q

Cyclic photophosphorylation uses only ____

A

PSI

41
Q

Cyclic photophosphorylation produces only ____ _______ of _____

A

small amounts of ATP

42
Q

Where does the light-independent reaction (aka Calvin cycle) take place?

A

Takes place in the stroma

43
Q

___ and ___ required to keep Calvin cycle going

A

ATP and protons

44
Q

Name the 3 stages in the light-independent reaction

A
  1. Carbon dioxide + RuBP = 2x of GP
  2. ATP + reduced NADP = Reduction of GP → TP
  3. RuBP is regenerated
45
Q

The Light-independent Reaction

Describe stage 1

A
  1. Carbon dioxide enters through stomata & diffuses into stroma
  2. Carbon dioxide combines with RuBP
    • Catalysed by enzyme rubisco
  3. Gives an unstable 6C which breaks down quickly into 2x GP (3C)
46
Q

The Light-independent Reaction

Describe stage 2

A
  1. (Hydrolysis of) ATP provides energy to change GP → TP (3C)
  2. Reduced NADP provides H+ ions so it can reduce GP → TP
  3. Reduced NADP is recycled to NADP
  4. TP is then converted into useful organic compounds (e.g. glucose) & some continues in Calvin cycle to regenerate RuBP
47
Q

The Light-independent Reaction

Describe stage 3

A
  1. 5/6 of TP produced used to regenerate RuBP NOT make hexose sugars
  2. Regenerating RuBP uses rest of ATP produced by light-dependent reaction
48
Q

What are TP and GP molecules used to make?

A

Carbohydrates, lipids and amino acids

49
Q

Describe how hexose sugars made (carbohydrates)

A

Made by joining 2 TP molecules together

50
Q

Draw the Calvin cycle (include the no. of carbons)

A
51
Q

Describe how larger carbohydrates (e.g. sucrose, starch, cellulose) are made

A

Made by joining hexose sugars together in different ways

52
Q

Describe how lipids are made

A

Made using glycerol, which is synthesised from TP, and fatty acids, which are synthesised from GP

53
Q

Describe how some amino acids are made

A

Some amino acids are made from GP

55
Q

What are coenzymes?

A

Molecules that aids function of an enzyme

56
Q

How do coenzymes work?

A

Work by transferring a chemical group from 1 molecule to another

57
Q

Name a coenzyme in photosynthesis

A

NADP

58
Q

Explain how NADP is a coenzyme

A
  • Transfers hydrogen from 1 molecule to another
  • Means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule
59
Q

Name 3 limiting factors of photosynthesis

A
  1. Light intensity
  2. Temperature
  3. Carbon dioxide concentration
60
Q

Describe how light intensity affects the rate of photosynthesis

A
  • Higher intensity of light = more energy for light-dependent reaction
  • Rate of photosynthesis ↑
61
Q

Describe and explain what happen to the rate of photosynthesis at high temperatures.

A
  • High temps = enzymes denature
    • Photosyntheis stops
  • High temps = stomata close to avoid losing too much water
    • Causes photosynthesis to slow down because less carbon dioxide enters leaf when stomata are closed
62
Q

Name a use suitable statistical test to investigate correlation between light intensity and rate of photosynthesis

A

Spearmen’s rank (correlation coefficient)

63
Q

What does Spearmen’s rank allow you to do?

A

Allows you to work out the degree to which 2 sets of data are correlated

64
Q

What is Spearmen’s rank given as (name the range of the values)?

A

Given as value between 1 and -1

65
Q

Describe and explain how an increase in temperature and a reduction in light intensity will affect the growth of plants. (3)

A
  • Growth will decrease (at higher temperature)
  • Rate of respiration will increase at higher temperature
  • Photosynthesis decreases as there’s less light
66
Q

ADP levels can be a ____ ______

A

limiting factor

67
Q

Explain why it is important for plants to produce ATP during respiration in addition to during photosynthesis. (5)

A
  • In dark, no ATP production in photosynthesis
  • Some tissues unable to photosynthesis/produce ATP
  • ATP can’t be stored
  • Plant uses more ATP than produced in photosynthesis
  • ATP for active transport
68
Q

Herbicides affect the light-dependent reaction (namly the production of oxygen and the electron transport chain).

Suggest how herbicides cause a reduction in the production of oxygen by plants (3)

A
  • Binds to chlorophyll molecules
  • Stops release of electrons from chlorophyll
  • Stops movement of electrons down electron transport chain
  • therefore the break down of water reduces
69
Q

Herbicides affect the light-dependent reaction (namly the production of oxygen and the electron transport chain).

Suggest how herbicides cause the death of plants (3)

A
  • Less ATP
  • For light-independent reaction
  • therefore less sugars produced for respiration
  • Rate of respiration is greater than rate of photosynthesis
70
Q

Explain why high levels of oxygen reduce the rate of photosynthesis (effect is greater at higher temperatures). (2)

A
  • More RuBP combines with oxygen than carbon dioxide
  • Competitive inhibition (for rubisco)
    • Less RuBP regenerated

AQA A Level Biology Paper 2 (16 decks)

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