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A2 Biology > Photosynthesis > Flashcards

Photosynthesis Flashcards

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1
Q

Identify environmental factors that limit the rate of photosynthesis

A
  • light intensity (light-dependent stage)
  • co2 levels (light-independent stage)
  • temperature
  • mineral/Mg levels
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2
Q

Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis

A
  • artificial light, esp at night
  • artificial heating
  • addition of co2 to greenhouse atmosphere
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3
Q

Where do the light-dependent and light-independent reactions occur in plants

A

light-dependent: in the thylakoids of chloroplasts
light-independent: stroma of chloroplasts

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4
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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5
Q

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

A
  • electron transfer chain
  • chemiosmosis
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6
Q

What happens in the electron transfer chain

A

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

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7
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 the thylakoid space

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8
Q

How does chemiosmosis produce ATP in the light-dependent stage

A

H+ ions move down their conc gradient from the thylakoid space into the stroma via the channel protein ATP synthase

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9
Q

Explain the role of light in photolysis

A

light energy splits molecules of water

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10
Q

What happens to the products of the photolysis of water

A
  • H+ ions: move out of thylakoid space via ATP synthase and 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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11
Q

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

A
  • NADP + 2H+ + 2e- to reduced NADP
  • catalysed by dehydrogenase enzymes
  • stroma of chloroplasts
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12
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
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13
Q

Name the 3 stages of the Calvin cycle

A

1- carbon fixation
2- reduction
3- regeneration

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14
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 glycerine 3-phosphate (GP)
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15
Q

What happens during reduction in the Calvin cycle ?

A
  • 2x GP are reduced to 2x triose phosphate (TP)
  • requires 2x reduced NADP and 2x ATP
  • forms 2x NADP and 2x ADP
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16
Q

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

A

1C leaves the cycle (some of the TP is converted into useful organic molecules

17
Q

What happens during regeneration in the Calvin cycle?

A
  • after 1C leaves the cycle, the 5C compound RuP forms
  • RuBP is regenerated from RuP using 1x ATP
  • forms 1x ADP
18
Q

State the roles of ATP and reduced NADP in the light-independent reaction

A
  • ATP: reduction of GP to TP and provides phosphate group to convert RuP into RuBP
  • reduced NADP: coenzyme transports electrons needed for reduction of GP to TP
19
Q

State the no of carbon atoms in RuBP, GP, TP

A

RuBP: 5
GP: 3
TP: 3

20
Q

Describe the structure of a chloroplast

A
  • usually disc shaped
  • double membrane
  • thylakoids: flattened discs stack to form grana
  • intergranal lamellae: tubular extensions attach thylakoids in adjacent grana
  • stroma: fluid filled matrix
21
Q

how does the structure of the chloroplast maximise the rate of the light-dependent reaction

A
  • ATP synthase channels within granal membrane
  • large surface area of thylakoid membrane for ETC
  • photosystems position chlorophyll to enable maximum absorption of light
22
Q

how does the structure of the chloroplast maximise the rate of the light-independent reaction?

A
  • own DNA and ribosomes for synthesis of enzymes e.g rubisco
  • concentration of enzymes and substrates in stroma is high
23
Q

define limiting factor

A

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

24
Q

Why do farmers try to overcome the effect of limiting factors

A
  • to increase yield
  • additional cost must be balanced with yield to ensure maximum profit
25
Q

suggest how a student could investigate the effect of a named variable on the rate of photosynthesis

A

dependent variable: rate of O2 production/ CO2 consumption
1- use a potometer
2- place balls of calcium alginate containing green algae in hydrogen carbonate indicator (colour change orange to magenta, as CO2 is consumed and pH increases)

26
Q

state the purpose and principle of paper chromatography

A

molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (chromatography paper)

27
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

28
Q

outline how paper chromatography can be used to separate photosynthetic pigments

A

1- use a capillary tube to spot pigment extract onto pencil ‘start line’ (origin) 1cm above bottom of paper
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 different distances

29
Q

what are Rf values? how can they be calculated

A
  • ratios that allow comparison of how far molecules have moved in chromatograms
  • Rf value= distance between origin and centre of pigment spot/ distance between origin and solvent front

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