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Paper 1 - Bio > Photosynthesis > Flashcards

Photosynthesis Flashcards

1
Q

Chloroplast

A

An organelle found in plants and green algae that is the site of photosynthesis.

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2
Q

Describe the structure of chloroplast.

A
  • Double membrane (chloroplast envelope).
  • Grana (stacks of flattened disks (thylakoids) that contain photosystem I and II, electron transport chain, ATP synthase.
  • Grana connected by intergranal lamellae.
  • Stroma (fluid-filled matrix containing enzymes).
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3
Q

Where are chloroplasts located in a leaf?

A

Mainly found in the palisade layer.

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4
Q

How are chloroplasts adapted for photosynthesis?

A
  • Thylakoids give a large surface area for light-dependent reactions.
  • Photosynthetic pigments arranged into photosystems to maximise light absorption.
  • Stroma directly surrounds grana (products of photosynthesis diffuse directly into the stroma.
  • Contain their own DNA (cpDNA) and ribosomes.
  • Inner chloroplast membrane less permeable than outer, enabling control over the movement of substances.
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5
Q

How are angiosperm leaves adapted for photosynthesis?

A
  • Large surface area to maximise light absorption.
  • Thin to reduce the diffusion distance for carbon dioxide.
  • Upper epidermis transparent allowing light to strike mesophyll layers.
  • Palisade cells densely packed and contain many chloroplasts.
  • Air spaces reduce diffusion distance for carbon dioxide.
  • Vein network transports water and minerals to the leaf and takes sugars away.
  • Stomata allow carbon dioxide to diffuse into the leaf.
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6
Q

What is a transducer? Why are chloroplasts described as transducers?

A
  • Something that converts one type of energy into another.

- Chloroplasts transduce light energy into the chemical energy of ATP.

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7
Q

What is a photosynthetic pigment?

A

A molecule present in chloroplasts (or photosynthetic bacteria) that absorbs light energy for photosynthesis. It absorbs specific wavelengths of light and reflects others.

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8
Q

Give some examples of photosynthetic pigments.

A
  • Chlorophylls a and b
  • Beta carotene
  • Xanthophylls
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9
Q

What is the purpose of chromatography?

A

To separate different products from a mixture.

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10
Q

What is photosynthesis?

A

A complex metabolic pathway that synthesises organic molecules from carbon dioxide and water in the presence of light.

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11
Q

What is a photosystem?

A
  • Protein complex consisting of an antenna complex and reaction centre.
  • Involved in the absorption of light and transfer of electrons in photosynthesis.
  • Two types: PSI and PSII.
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12
Q

How do PSI and PSII differ?

A

They absorb different wavelengths of light.

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13
Q

Describe the process of light harvesting in photosynthesis.

A
  • Antenna complex absorbs light energy of varying wavelengths and transfers it quickly and efficiently to the reaction centre.
  • Energy absorbed by two chlorophyll a molecules which emit “excited” electrons.
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14
Q

What is an absorption spectrum?

A

A pattern of bands that occurs when a substance absorbs the different wavelengths of light.

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15
Q

What is an action spectrum?

A

A graph of the rate of photosynthesis against each wavelength of light absorbed by a pigment.

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16
Q

Describe the light-dependent stage of photosynthesis.

A
  • First stage of photosynthesis.
  • Takes place in the thylakoids of the chloroplast.
  • Uses light energy to produce ATP, reduced NADP and oxygen.
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17
Q

State the two processes of ATP generation by the light-dependent reactions.

A

Cyclic and non-cyclic photophosphorylation.

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18
Q

Define cyclic photophosphorylation.

A

The formation of ATP involving PSI only, where NADP+ is not reduced.

19
Q

Outline cyclic photophosphorylation.

A
  • Involves PSI only (no electron supplied by PSII).
  • Excited electrons enter the ETC to produce ATP and then return to PSI.
  • No reduction of NADP and no water required to replace lost electrons.
20
Q

What is the purpose of cyclic photophosphorylation?

A

Produces additional ATP to meet surplus energy demands of the cells.

21
Q

Define non-cyclic photophosphorylation.

A

The formation of ATP and reduced NADP involving both PSI and PSII.

22
Q

Outline non-cyclic photophosphorylation.

A
  • Involves PSI and PSII.
  • Excited electrons enter the ETC to produce ATP.
  • NADP acts as a final acceptor and is reduced.
  • Water is photolysed to compensate for electrons lost from PSII.
23
Q

What is the purpose of non-cyclic photophosphorylation?

A

Produces ATP and reduced NADP for the Calvin cycle.

24
Q

How does chemiosmosis produce ATP in the light-dependent stage?

A
  • Protons flow down their concentration gradient from the thylakoid space into the stroma via ATP synthase.
  • ATP synthase phosphorylates ADP to form ATP as protons flow through it.
25
Q

Describe photolysis.

A

The splitting of a molecule of water in the presence of light (energy from the sun) that occurs during the light-dependent stage of photosynthesis. This produces protons, electrons and oxygen.

26
Q

What happens to the products of photolysis?

A
  • H+ (used in proton pumping and to reduce NADP).
  • e- (replaces electrons lost from chlorophyll a in PSII).
  • Oxygen (by-product, used for respiration of diffuses out of the leaf as waste gas).
27
Q

Explain how the ETC results in the production of reduced NADP.

A

NADP acts as a final electron acceptor, and is subsequently reduced.

28
Q

Describe the light-independent stage of photosynthesis.

A
  • Second stage of photosynthesis.
  • Calvin cycle produces glucose.
  • Does not require light energy and takes place in the stroma.
  • Uses carbon dioxide and the products of the light-dependent stage to build organic molecules.
29
Q

What is the light-independent stage also known as?

A

The Calvin cycle.

30
Q

Name the three main stages of the Calvin cycle.

A
  1. Carbon fixation
  2. Reduction
  3. Regeneration
31
Q

What happens during carbon fixation of the Calvin cycle?

A
  • Reaction between carbon dioxide and ribulose bisphosphate (RuBP) catalysed by enzyme RuBisCo.
  • Forms unstable 6C intermediate that breaks down into two molecules of glycerate 3-phosphate (G3P).
32
Q

What happens during reduction of the Calvin cycle?

A
  • 2xG3P are reduced to 2x triose phosphate (TP).
  • Requires 2x reduced NADP and 2x ATP formed during the light-dependent reaction.
  • Forms 2x NADP and 2xADP that enters the light-dependent reaction.
33
Q

What happens during regeneration of the Calvin cycle.

A
  • After 1C leaves the cycle, the 5C compound ribulose monophosphate (RuB) forms.
  • Ribulose bisphosphate (RuBP) is regenerated from RuP using 1x ATP
34
Q

How are nutrients produced as a result of photosynthesis?

A
  • Formation of amino acids from GP (requires nitrates and sulfates).
  • TP molecules used to produce sugars e.g. glucose, fructose and sucrose.
35
Q

What is a limiting factor?

A

A variable that limits the rate of a particular reaction.

36
Q

Name the factors that limit the rate of photosynthesis. What stage do they limit?

A
  • Light intensity (light-dependent stage).
  • Light wavelength (absorption by chlorophyll).
  • Carbon dioxide concentration (light-independent stage).
  • Temperature (enzyme-controlled reactions (carbon fixation)).
  • pH (enzyme-controlled reactions).
37
Q

What happens during regeneration of the Calvin cycle.

A
  • After 1C leaves the cycle, the 5C compound ribulose monophosphate (RuB) forms.
  • Ribulose bisphosphate (RuBP) is regenerated from RuP using 1x ATP
38
Q

How are nutrients produced as a result of photosynthesis?

A
  • Formation of amino acids from GP (requires nitrates and sulfates).
  • TP molecules used to produce sugars e.g. glucose, fructose and sucrose.
39
Q

What is a limiting factor?

A

A variable that limits the rate of a particular reaction.

40
Q

Name the factors that limit the rate of photosynthesis. What stage do they limit?

A
  • Light intensity (light-dependent stage).
  • Light wavelength (absorption by chlorophyll).
  • Carbon dioxide concentration (light-independent stage).
  • Temperature (enzyme-controlled reactions (carbon fixation)).
  • pH (enzyme-controlled reactions).
41
Q

Describe the role of nitrogen in plant metabolism.

A

Synthesis of amino acids, nucleotides and chlorophyll.

42
Q

What does nitrogen deficiency in plants cause?

A
  • Stunted growth.

- Chlorosis (yellowing of the leaves due to insufficient chlorophyll production).

43
Q

Describe the role of magnesium in plant metabolism.

A

Central component of chlorophyll.

44
Q

What does magnesium deficiency in plants cause?

A

Chlorosis (yellowing of the leaves due to insufficient chlorophyll production).

Paper 1 - Bio (5 decks)

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