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Y13 Biology > Topic 5 A: Photosynthesis > Flashcards

Topic 5 A: Photosynthesis Flashcards

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1
Q

Simple definition of photosynthesis?

A

Process where energy from light is used to make glucose from water and carbon dioxide.

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2
Q

Why is photosynthesis considered a metabolic pathway?

A

Contains lots of small reactions controlled by enzymes.

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3
Q

Equation for photosynthesis?

A

6CO2 + 6H2O = C6H12O6 + 6O2

carbon dioxide + water = glucose + oxygen

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4
Q

Can plants simply use the glucose?

A

No, they must turn it into ATP first. Which acts as an immediate source of energy.

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5
Q

ATP and phosphorylation?

A
  • adding a phosphate group
  • ADP + Pi = ATP (condensation reaction)
  • ATP synthase catalyses reaction
  • energy stored in phosphate bond
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6
Q

ATP and hydrolysis?

A
  • breaking down ATP
  • one phosphate bond broken
  • ATP hydrolase catalyses reaction
  • small amount of energy released from bond
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7
Q

Properties of ATP? (5)

A
  • releases a small amount of energy, so none wasted.
  • easily broken down as one bond is broken.
  • ATP can’t pass out of cells so they will always have energy.
  • it can make other molecules more reactive by adding a phosphate.
  • its small and soluble so easily transported around the cell.
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8
Q

Exam Question: Humans synthesise more than their body mass of ATP each day. Explain why it is necessary to synthesise such large amounts of ATP? (3)

A
  • ATP cannot be stored/ immediate energy source
  • ATP only releases small amount of energy
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9
Q

What is the thylakoid?

A

folded membranes provide large surface area.
photosynthetic proteins (chlorophyll) and electron carrier proteins are embedded.

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10
Q

What is the stroma?

A

fluid-filled matrix which is filled with enzymes.

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11
Q

What are photosystems?

A

Pigments that are attached to the proteins in the thylakoid membranes.

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12
Q

What are the two different photosystems?

A
  1. PSI - has primary pigment that absorbs light best at wavelength of 700nm.
  2. PSII - has primary pigment that absorbs light best at wavelength 680nm.
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13
Q

What kind of reaction occurs in photosynthesis?

A

Redox reactions.

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14
Q

OILRIG?

A

Oxidation is loss (of electrons)
Reduction is gain (of electrons)

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15
Q

All about oxidation?

A
  • losing electrons and hydrogen
  • gaining oxygen
  • exothermic as energy is given out to surroundings
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16
Q

All about reduction?

A
  • gaining electrons and hydrogen
  • losing oxygen
  • endothermic as energy is taken in from surroundings
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17
Q

4 steps of light dependent reaction?

A
  1. photoionisation
  2. photolysis
  3. ATP and reduced NAPD
  4. chemiosmosis
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18
Q

Photoionisation simple definition?

A

Electrons being lost from cholorphyll using light energy.

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19
Q
  1. Photoionisation process? Part one
A
  1. light energy is absorbed by chlorophyll in PSII - this excited electrons within chlorophyll.
  2. as excited electrons gain more energy, they leave the chlorophyll molecule - chlorophyll has been ionised.
  3. high energy electrons released and move down the electron transport chain to PSI by electron carriers.
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20
Q
  1. Photoionisation process? Part two
A
  1. electrons lose energy at each stage - electrons passed along a number of electron carriers - each one at a slightly lower energy level.
  2. electron carriers are reduced and chlorophyll is oxidised.
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21
Q

Light energy is used for?

A
  1. ATP
  2. Reduced NADP
  3. Splitting water
22
Q

Photolysis simple definition?

A

Splitting water into H+ ions, electrons and oxygen.

23
Q
  1. Photolysis process?
A
  1. any electrons that left PSII (due to too much energy) are replaced by electrons from the photolysis of water.
  2. H+ ions/protons are picked up by NADP (co-enzyme) which forms NADPH
  3. oxygen is a waste product - can be used in respiration or diffuses out of leaf through stomata.
24
Q

What does PSII contain that aids the splitting of water?

A

Water splitting enzyme called oxygen evolving complex.

25
Q

Splitting of water equation?

A

H20 = 1/2 O2 + 2e- + 2H+

26
Q
  1. Reduced NADP simple definition and function?
A

Excited electrons and h+ ions combine with NADP.
- provides H/electrons for GP or reduces GP to TP

27
Q

Equation for reduced NADP?

A

2H+ + 2e- + NADP = NADPH

28
Q

Role of a co-enzyme?

A

Transfer a chemical group from one molecule to another.
E.g., transferring hydrogen to NADP to form NADPH.

29
Q
  1. Chemiosmosis simple definition?
A

Electrons create proton gradient to drive ATP synthesis.

30
Q
  1. Chemiosmosis process?
A
  1. electrons pass through transport chain and release energy
  2. active transport of H+ ions/protons from stroma to thylakoid lumen
  3. electrochemical gradient created
  4. facilitated diffusion of H+ ions/protons from thylakoid lumen to stroma
  5. happens through enzyme ATP synthase
  6. ATP synthase also helps catalysing ADP+Pi = ATP
  7. proton movement through ATP synthase causes it to change shape to catalyse reaction
31
Q

Exam question: Crops use light energy to produce photosynthetic products. Describe how crop plants use light energy during the light-dependent reaction? (5)

A
  1. light energy excites electrons
  2. electrons move along electron transfer chain, releasing energy
  3. energy used to ADP+Pi=ATP
  4. photolysis of water produces protons, electrons and oxygen
  5. NADP reduced by electrons (NADPH)
32
Q

What is non cyclic photophosphorylation?

A
  • type one
  • both photosystems used
  • three products: ATP, reduced NADP, and oxygen
33
Q

What is cyclic photophosphorylation?

A
  • type two
  • only involves photosystem one
  • only product: ATP in small amounts
34
Q

What do ATP and reduced NADP produce?

A

Complex organic substances e.g., starch, sugar, and cellulose.

35
Q

What doesn’t the light independent reaction require?

A

Light

36
Q

Where does the LIR occur?

A

Stroma

37
Q

LIR steps?

A
  1. carbon fixation
  2. reduction of GP
  3. regeneration of RuBP
38
Q

Carbon fixation process?

A

‘the removal of co2 from the environment to become part of the plant’
- co2 enters leafe through stomata and diffuses into stroma
-co2 reacts with ruBP (ribulose biphosphate) which is catalysed by rubisco
-this creates an unstable 6C compound so splits into 2 GP molecules (3C)

39
Q

Reduction of GP (glycerate 3-phosphate) process?

A

‘the gaining of hydrogen by GP and the reoxidation of NADP’
- 2 ATP hydrolysed to provide energy for conversion of GP into TP (triose phosphate)
- conversion also requires H+ ions, hydrogen in 2 reduced NADP is picked up by GP molecule (reduced), and NADP is being re-oxidised
- 2 re-oxidised NADP goes back to LDR to be reduced again

40
Q

Regeneration of RuBP process?

A

‘to ensure RuBP is recycled to be used for another cycle’
- one of the 6 carbon atoms ( from two 3C TP ) is removed from the cycle each time it happens. the cycle needs to turn 6 times to create a hexose sugar
(hexose sugar creates useful organis substances e.g, lipids and amino acids)
- the remaining 5c used to regenerate RuBP, also requires ATP energy.

41
Q

The maths within the regeneration of RuBP?

A
  • 3 turns of the cycle produces 6 molecules of TP because two molecules of TP are made for every one co2 molecule used.
  • 6 turns of the cycle needs 18 ATP (3 for each cycle)
  • 6 turns of the cycle needs 12 NADPH (2 in each cycle)
42
Q

Overall products used in regeneration of RuBP?

A

1 co2
3 ATP
2 NADPH
2 TP
1/6 of hexose sugar

43
Q

Why cant LIR happen in darkness? (2)

A

Requires ATP and reduced NADP from LDR, and inputs would run out without light

44
Q

LDR products needed by LIR

A

ATP - hydrolysis provides energy for reaction
NADPH - donates a hydrogen atom to reduce GP
C02 - from atmosphere

45
Q

What is LIR also known as?

A

The calvin cycle

46
Q

Exam question: During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. (6)

A
  1. co2 combines with RuBP
  2. produces two GP
  3. GP reduced to TP
  4. using reduced NADP
  5. using energy from ATP
  6. TP converted to glucose
47
Q

Light intensity affecting rate of photosynthesis?

A
  • at lower light intensities, the increase in the rate is linear.
  • reaches saturation point and then another factor becomes the limiting factor
  • after, the graph levels off and rate is constant
  • greater light intensity = more energy supplied = faster LDR
  • produces more ATP & reduced NADP for the calvin cycle, so faster LDR
48
Q

Agricultural use of light?

A
  • aim to prevent light becoming limiting factor
  • e.g., using glass materials and lamps
49
Q

Carbon dioxide affecting rate of photosynthesis?

A
  • at lower concentrations the increase in rate is linear
  • reaches saturation point and then another factor becomes limiting factor
  • after, graph levels off and rate is constant
  • CO2 is one of the reactants entering calvin cycle, the more CO2 present = faster photosynthesis
50
Q

Agricultural use of co2?

A
  • aim to ensure co2 isnt limiting factor
  • e.g., burning prophane in generator produces more co2
51
Q

Temperature affecting rate of photosynthesis?

A
  • rate increases as temperature increases due to number of collisions between substrates and enzymes increasing
  • reaches optimum temperature and then enzymes begin to denature and rate decreases
  • calvin cycle affected by temperature as LIR is enzyme-controlled e.g., rubisco
  • temperature has no significant effect on LDR as its driven by light energy.
52
Q

Agriculture usage of temperature?

A
  • aim to manipulate temperature
  • e.g., heaters, coolers, and air circulation

Y13 Biology (11 decks)

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