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A-Level AQA Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

Photosynthesis

A

A complex metabolic pathway that consists of three main stages:

  1. Capturing of light energy
  2. Light-dependent reaction
  3. Light-independent reaction.

Overall, in the presence of light:

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2
Q

Equation for photosynthesis

A

6CO₂ ​+6H₂​O​ ⟶C​H​₁₂O​₆ ​​+ 6O₂​

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3
Q

Site of photosynthesis

A

Chloroplasts

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4
Q

The 10 adaptations of a leaf:

Name at least 5

A
  • Large surface area
  • Arrangement of leaves on the plant that minimises overlapping and so avoids the shadowing of one leaf by another
  • Thin so this keeps diffusion short
  • Transparent cuticle
  • Numerous stomata for gases exchange
  • Long and narrow upper mesophyll cells packed with chloroplasts that collect sunlight
  • Stomata open and close in response to changes in light intensity
  • Many air spaces in the lower mesophyll layer to allow rapid diffusion in the gas phase of co2 and o2
  • A network of xylem that brings water to the leaf cells and phloem that carries away the sugars produced during photosynthesis
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5
Q

Light-dependent reaction

A

​The 2nd stage of photosynthesis that uses light energy to produce ATP, reduced NADP and oxygen (by-product).

takes place in the thylakoids of the chloroplast.

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6
Q

Light-independent reaction (Calvin cycle)

A

The third stage of photosynthesis, in which the products of the light-dependent stage and carbon dioxide are used to form a simple sugar.

This stage does not require light energy and takes place in the stroma of the chloroplast.

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7
Q

Limiting Factor

A

​A variable that limits the rate of a particular reaction.

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8
Q

What is the 3 thing included in the structure of chloroplasts

A

Grana
Thylakoid
Stroma

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9
Q

Where does light independent &light dependant reactions take place in plants.

A

Light-in dependant: Stroma of chloroplasts

Light dependant: in the thylakoids

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10
Q

Raw material involved in photosynthesis

A

Water

Carbon dioxide

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11
Q

Products of light-dependent reaction

A

Reduced NADP, ATP, Oxygen

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12
Q

Products of a light-independent reaction

A

Sugars and others organic molecules

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13
Q

Explain the role of light in photoionisation

A

Chlorophyll molecules absorbs energy from photons of light.

This ‘excites’ 2 electrons (raises them to a higher energy level), causing them to be released from the chlorophyll.

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14
Q

Name the 2 main stages involved in ATP production in light-dependant reaction

A
  1. Electron transfer chain

2. Chemiosmosis

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15
Q

What happens in the electron transfer chain (ETC)?

A

Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & undergo a series of redox reactions, which releases energy

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16
Q

Oxidation

A

Loss of electrons of hydrogen or gain of oxygen

17
Q

Reduction

A

Gain of electrons or gain of hydrogen or loss oxygen

18
Q

How is a proton concentration gradient established during chemiosmosis?

A

Some energy released from the ETC is coupled to the active transport of H+ ions (protons) from the stroma into thylakoid space.

19
Q

How does chemiosmosis produce ATP in light-dependant stage?

A

H+ ions (protons) move down their concentration gradient from the thylakoid space into the stroma via the channel protein ATP synthase.

20
Q

Explain the role of light in photolysis

A

Light energy splits molecules of water

2H₂O → 4H⁺ + 4e⁻ + O₂

21
Q

What happens to the products of photolysis of water?

A
  • H ⁺ ions: move out of thylakoid space via ATP synthase & are used to reduce the coenzyme NADP.
  • e⁻ : Replaces electrons lost from chlorophyll.
  • O₂: used for respiration or diffuses out of leaf waste gas.
22
Q

How and where is reduced NADP produced in the light-dependant reaction?

A
  • NADP + 2H ⁺ + e⁻ → reduced NADP.
  • Catalysed by dehydrogenase enzymes.
  • Stroma of chloroplasts
23
Q

Where do the H ions and electrons used to reduce NADP come from?

A
  • H ions: photolysis of water

- Electrons: NADP acts as the final electron acceptor of the electron transfer chain.

24
Q

Name the 3 main stages of the Calvin cycle.

A
  1. Carbon fixation
  2. Reduction
  3. Regeneration
25
Q

What happens during carbon fixation?

A
  • Reaction between CO₂ & ribulose bisphosphate (RuBP) catalysed by rubisco
  • Forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)
26
Q

What happes during reduction (in the calvin cycle)?

A
  • 2 X GP are reduced to 2 x triose phosphate (TP)
  • Required 2 x reduced NADP & 2 x ATP
  • Forms 2 x NADP & 2 x ADP
27
Q

How does the light-independant reaction result in the production of useful organic substances?

A

1C leaves the cycle (i.e. some of the TP is converted into useful organic molecules).

28
Q

What happens during regeneration (in the calvin cycle)?

after

A
  • After 1C leaves the cyle, 5C compound RuP forms
  • RuBP is regenerated from RuP using 1x ATP
  • Form 1 x ADP
29
Q

Outline the seqeuence of events in the light-independant reaction (Calvin cycle).

A

Refer to PMT

30
Q

State the roles of ATP & (reduced) NADP in the light-indepent reaction

Reduction

transports

A

ATP: reduction of GP to TP & provides phosphate group to convert RuP into RuBP.

  • (Reduced) NADP: Coenzyme transports electrons needed for reduction of GP to TP.
31
Q

State the number of Carbon atoms in RuBP, GP & TP.

A

RuBP: 5
GP : 3
TP : 3

32
Q

Describe the structure of a chloroplast.

5

Flattened
Intergranal
Fluid F

A
  • Usually disc-shaped
  • Doubled membrane (envelope)
  • Thylakoids: flattend discs stack to form grana
  • Intergranal lamellae: tubular extensions attach thylakoids in adjacent grana.
  • Stroma: fluid-filled matrix.
33
Q

How does the structure of the chloroplast maximise the rate of the light-dependent reaction?

A
  • ATP synthase channels within granal membrane.
  • Large SA of thylakoid membrane for ETC.
  • photosystems postion chlorophyll to enable maximum absorption of light.
34
Q

How does the structure of the chloroplasts maximise the rate the light-independent reaction?

A
  • Own DNA & ribosomes for synthesis of enzymes e.g. rubisco.

- Concentration of enzymes & substrates in stroma is high.

35
Q

Name 4 enviromentl factors that can limit the rate of photosynthesis.

A
  • Light intensity (Light-dependent stage).
  • Co₂ levels (light-independent stage).
  • Temperature (enzyme-controlled steps).
  • Mineral/magnesium levels (maintain normal functioning of chlorophyll).

A-Level AQA Biology (77 decks)

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