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Biology OCR > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

How are photosynthesis and respiration related ?

A
  • CO² & H²O are the raw materials for photosynthesis and the products of respiration
  • O² & glucose are the raw ,materials for respiration and the products of photosynthesis
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2
Q

Describe the structure of chloroplast

A
  • Usually disc shaped
  • Double membrane (envelope)
  • Thylakoids : flattened discs stacked to form grana
  • Intergranal lamellae : tubular extensions attach thylakoids in adjacent grana
  • Stromatolites : fluid-filled matrix with high enzyme & substrate concentration & own loop of DNA

Refer to GoodNotes

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3
Q

Where do the light-dependent & light-independent reactions occur in plants ?

A
  • Light-dependent: in the thylakoids of chloroplast
  • Light-Independent: Stroma of chloroplast
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4
Q

What is the role of photosynthetic pigments ? Name the 2 main groups

A

Embedded within thylakoid membrane. Absorb different wavelengths of light to maximise rate of photosynthesis
- Primary pigment : chlorophyll (made of chlorophyll A & chlorophyll B) found in photosystems
- Accessory pigments : carotenoids (carotene & xanthophylls) found in light harvesting systems

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5
Q

Name the processes in light-dependent reactions

A
  • Photoionisation
  • electron transfer chain
  • Chemiosmosis
    Non-cyclic only:
  • Reduction of NADP
  • Photolysis of water
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6
Q

Explain the role of light in photoionisation

A
  • Chlorophyll molecules absorb 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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7
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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8
Q

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

A
  • Some energy released from the ETC is coupled to active transport of H+ ions from Stroma into thylakoid space
  • H+ ions move down concentration gradient from thylakoid pace into Stroma via transmembrane channel protein ATP synthase
  • ATP synthase catalyses ADP + Pi —> ATP
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9
Q

Describe non-cyclic photophosphorylation

A
  • Uses Photosystems I & II. Excited electrons Enter ETC to produce ATP. NADP acts as final electron acceptor & is reduced. Water is undergoes photolysis to release electrons replacing those lost from PS II
  • Purpose is to produce ATP & reduced NADP for Calvin cycle to produce biological compounds
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10
Q

Describe cyclic photophosphorylation

A
  • Uses only Photosystem I . Excited electrons enter ETC to produce ATP then return directly to photosystem (so no reduction of NADP & no water needed to replace lost electrons)
  • Purpose is to produce additional ATP to meet surplus energy demands of cell
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11
Q

What happens in photolysis of water ?

A

Light energy splits molecules of water
2H²O —> 4H+ + 4e- + O²

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12
Q

What happens to the products of the photolysis of water ?

A
  • H+ ions : move out thylakoids space via ATP synthase & are used to reduce the coenzyme NADP
  • e- : replace electrons lost from chlorophyll
    O² : used for respiration or diffuses out of leaf as waste gas
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13
Q

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

A
  • NADP + 2H+ (from photolysis of water) + 2e- (from acting as final electron acceptor in ETC) —> reduced NADP
  • Catalysed by dehydrogenase enzymes
  • Stroma of chloroplasts
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14
Q

Name the 3 main stages in the light-independent reaction

A
  1. Carbon Fixation
  2. Reduction
  3. Regeneration
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15
Q

What happens during carbon fixation ?

A
  • Reaction between CO² & ribulose bisphosphate (RuBP) catalysed by ribulose bisphosphate carboxylate (RuBisCo)
  • Forms useable 6C intermediate that breaks down into 2 x glycerate 3-phosphate
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16
Q

What happens during reduction in the light-independent reaction

A
  • 2 x glycerate 3-phosphate (GP) are reduced to 2 x triose phosphate (TP)
  • Requires 2 x reduced NADP & 2 x ATP
  • Forms 2 x NADP & 2 x ADP
17
Q

Outline the roles of Triose Phospahte from the light-independent reaction

A
  • Raw material : 1C leaves the cycle to produce monosaccharides, amino acids & other biological molecules
  • Involves in regeneration of RuBP: After 1C leaves cycle, the %C compound RuP forms. RuP is converted into RuBP using 1x ATP. Forms 1x ADP
18
Q

Outline the sequence of events in the light-independent reaction

A

Refer to GoodNotes

19
Q

State the number of Carbon atoms in RuBP, GP & GALP

A
  • RuBP : 5
  • GP : 3
  • GALP : 3
20
Q

Define limiting factor

A

Factor that determines maximum rate of a reaction, even if other factors change to become more favourable

21
Q

Name 4 environmental 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)
22
Q

How does light intensity affect the rate of photosynthesis?

A

Low light intensity = slower light-dependent reaction = less ATP & NADPH produced to convert GP to TP in light-independent reaction
- GP level rises
- TP levels falls = RuBP levels falls

23
Q

Define the implications of water stress

A
  1. Abscisic acid binds to complementary receptors on guard cell membrane, causing ca²+ ion channels on tonoplast to open. ca²+ ions diffuse from the vacuole into cytosol
  2. Positive feedback triggers other ion channels to open. Other ions e.g. K+ diffuse out of guard cell
  3. Water potential of guard cell becomes more positive. Water diffuses out via osmosis
  4. Guard cells become flaccid so stomata close
24
Q

State the purpose and principle of thin layered chromatography (TLC)

A

Molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (TLC plate, usually coated in a silicate)

25
Q

Outline a method for extracting photosynthetic pigments

A

Use a pestle and mortar to grind a leaf with an extraction solvent e.g. propanone

26
Q

Outline how TLC can be used to separate photosynthetic pigments

A
  1. Use a capillary tube to spot pigment extract onto pencil ‘start line’ (origin) 1 cm above bottom of plate .
  2. Place chromatography paper in solvent (origin should be above solvent level)
  3. Allow solvent to run until it almost touches the other end of the paper. Pigments move difference distances

Biology OCR (25 decks)

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