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A-Level Biology > Energy Transfers in and Between Organisms- Photosynthesis and Respiration ( Year 13 Content ) > Flashcards

Energy Transfers in and Between Organisms- Photosynthesis and Respiration ( Year 13 Content ) Flashcards

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1
Q

where do light-dependent and light-independent reactions occur in a plant?

A

light-dependent: thylakoid membrane
light-independent: stroma

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2
Q

Explain the role of light in photoionisation

A

-chlorophyll molecules absorb energy from the photons of light
-this excites 2 electrons to a higher energy level causing them to leave the chlorophyll molecule

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3
Q

what are the two main stages involved in ATP production during the light-dependent reaction?

A

-electron transport chain
-chemiosmosis

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4
Q

what happens in the electron transport?

A

electrons released from the chlorophyll move along a series of carrier proteins embedded in the thylakoid membrane in a series of redox reaction which releases energy

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5
Q

how is the H+ ( proton ) concentration gradient established during chemiosmosis?

A

energy released from the electron transport chain is used to actively pump H+ ions ( protons ) from the stroma to the thylakoid space

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6
Q

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

A

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

ATP catalyses ADP + Pi —> ATP

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7
Q

Explain the role of light in photolysis

A

light energy is used to split water molecules

2H2O —> 4H+ + 4e- + O2

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8
Q

what happens to the products from the photolysis of water?

A

H+ ions: move out the thylakoid space via channel protein ATP Synthase and are used to reduce coenzyme NADP
e- : replace the two electrons that had previously been lost from the chlorophyll
O2 : either used for aerobic respiration or leave through the stomata as waste product

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9
Q

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

A

● NADP + 2H+ + 2e- —> reduced NADP
● Catalysed by dehydrogenase enzymes
● Stroma of Chloroplast

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10
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 transport chain

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11
Q

Name the 3 main stages in the Calvin cycle

A

1) Carbon Fixation
2) Reduction
3) Regeneration

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12
Q

What happens during carbon fixation?

A

● Reaction between CO2 and ribulose biphosphate ( RuBP ) catalysed by rubisco
● Forms unstable 6C intermediate that breaks down into 2x glycerate-3-phosphate (GP)

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13
Q

What happens during reduction( in the Calvin cycle)

A

● 2x GP are reduced to 2x triose phosphate
● requires 2x NADPH and 2x ATP
● Forms 2x NADP and 2x ADP

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14
Q

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

A

1C leaves the cycle, 6 cycles forms a glucose molecule

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15
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

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16
Q

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

A

● ATP: reduction of Glycerate-3-phosphate to triose phosphate and provides phosphate groups to convert RuP into RuBP
● reduced NADP: coenzyme transports the electrons needed for reduction of GP to TP

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17
Q

State the number of carbon atoms in RuBP, GP and TP

A

RuBP: 5C
GP: 3C
TP: 3C

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18
Q

Describe the structure of a chloroplast

A

● usually disc shaped
● Double membrane
● Thylakoids: flattened discs stack to form grana
● intergranal lamella: tubular extensions attach thylakoids in adjacent grana
● Stroma: fluid-filled matrix

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19
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 areas of Thylakoid membrane for ETC
● photosystems position chlorophyll to enable maximum absorption of light

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20
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 such as rubisco
  • concentration of enzymes and substrates is high in the stroma
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21
Q

define ‘limiting factor’

A

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

22
Q

name 4 environmental factors that can determine the rate of photosynthesis

A
  • light intensity ( light-dependent stage )
  • CO2 levels ( light-independent stage )
  • Temperature ( enzyme-controlled steps )
  • mineral/magnesium levels ( maintains normal function of chlorophyll )
23
Q

outline some agricultural practices used to overcome the effects of limiting factors in photosynthesis

A
  • artificial lighting
  • artificial heating
  • addition of CO2 to create greenhouse atmosphere
24
Q

why farmers try to overcome the effects of limiting factors?

A
  • to increase yield
  • additional cost must be balanced with yield
25
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 )

26
Q

outline an method for extracting photosynthetic pigments

A

use a pestle and mortar to grind a leaf with an extra solvent ( propanone )

27
Q

outline how paper chromatography can be used to separate photosynthetic pigments

A

1) capillary tube to spot pigment extract onto pencil ‘start line’ ( origin ) 2 cm above the bottom of the paper
2) place chromatography paper in solvent ( origin should be above solvent level )
3) allow solvent to run until it almost touches the other ends of the paper. pigments move different distances

28
Q

what are Rf values? How can they be calculated?

A
  • Ratios that allow comparisons of how far the molecules have moved in chromatograms
  • Rf value = distance between origin and centre of pigment spot / distance between origin and solvent font
29
Q

what are the 4 main stages of aerobic respiration and where do they occur?

A
  • Glycolysis: cytoplasm
  • Link Reaction: mitochondrial matrix
  • Krebs cycle: mitochondrial matrix
  • Oxidative Phosphorylation: membrane of cristae
30
Q

outline the stages of glycolysis

A

1) glucose is phosphorylated to fructose biphosphate which requires 2x ATP
2) The fructose biphosphate is unstable so splits into 2x triose phosphate
3) triose phosphate is oxidised to 2x pyruvate which forms 2x reduced NAD
net gain of 2x reduced NAD and 2x ATP per glucose

31
Q

how does pyruvate from glycolysis enter the mitochondria?

A

active transport

32
Q

what happens during link reaction?

A

1) pyruvate is decarboxylated and then oxidised to form acetate and reduced NAD
2) the acetate combines with coenzyme A to form acetylcoenzyme A

33
Q

give a summary equation for the link reaction

A

pyruvate + NAD + coenzyme A —> acetyl coenzymeA + reduced NAD + CO2

34
Q

what happens in the krebs cycle?

A

1) acetyl coenzymeA reacts with a 4 carbon molecule which forms a 6 carbon molecule, at the same time coenzymeA is released and goes back to take part in the link reaction.
2) the 6 carbon molecule is decarboxylated and dehydrogenated which forms a molecule of CO2, reduced NAD and a 5 carbon molecule.
3) the 5 carbon molecule is further decarboxylated and dehydrogenated which forms a molecule of CO2, a molecule of reduced NAD and ATP from substrate level phosphorylation.
4) 2 more dehydrogenation reactions take place which forms a molecule of reduced NAD, a molecule of reduced FAD and the starting 4 carbon molecule

35
Q

what is the electron transport chain ( ETC )?

A

series of carrier proteins embedded in the membrane of the cristae of mitochondria
Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration

36
Q

what happens in the electron transport chain?

A

1) the electrons released from reduced NAD and FAD move along the electron transport chain in a series of redox reactions which releases energy
2) the energy released is coupled to maintaining proton gradient or released as heat energy
3) oxygen acts as a final electron acceptor

37
Q

how is the proton concentration gradient established during chemiosmosis in aerobic respiration?

A

the energy released from the electron transport chain is used to actively pump H+ ions from the mitochondrial matrix to the intermembrane space

38
Q

how is ATP produced during oxidative phosphorylation?

A

the H+ ions move down the concentration gradient from the intermembrane space to the mitochondrial matrix via channel protein ATP synthase
ATP synthase catalyses ADP + Pi —> ATP

39
Q

state the role of oxygen in aerobic respiration

A

final electron acceptor in the electron transport chain
O2 + 4H+ + 4e- —> 2H2O

40
Q

what is the benefit of the electron transport chain rather than a single reaction?

A
  • energy is released gradually
  • less energy is released as heat
41
Q

name 2 types of molecules that can be used as alternative respiratory substrates

A
  • amino acids from proteins
  • fatty acids and glycerol from lipids
42
Q

how can lipids act as an alternative respiratory substrate ?

A

Lipid —> glycerol + fatty acids
1) phosphorylation of glycerol —> triose phosphate for glycolysis
2) Fatty acids —> acetate
3) acetate enters link reaction
4) H atoms produced for oxidative phosphorylation

43
Q

how can amino acids act as an alternative respiratory substrate?

A

deamination produces
1) 3 carbon compounds —> pyruvate for link reaction
2) 4/5 carbon compounds —> intermediates in krebs cycle

44
Q

name the stages in respiration that produces ATP in substrate level phosphorylation

A
  • glycolysis ( anaerobic )
  • Krebs cycle
45
Q

what happens during anaerobic respiration in animals?

A

only glycolysis continues
reduced NAD + pyruvate —> oxidised NAD ( for further glycolysis ) + lactate

46
Q

what happens to the lactate produced during anaerobic respiration?

A

transported to the liver via the bloodstream, where it is oxidised to pyruvate.
it can enter the link reaction in liver cells or be converted into glycogen

47
Q

what happens during anaerobic respiration in plant cells and yeast?

A

only glycolysis continues
pyruvate is decarboxylated to form ethanal
ethanal is reduced to ethanol using reduced NAD to form oxidised NAD for further glycolysis

48
Q

what is the advantage of producing ethanol/lactate during anaerobic respiration

A

converts reduced NAD to NAD so glycolysis can continue

49
Q

what is the disadvantage of producing ethanol during anaerobic respiration?

A
  • cells die when ethanol concentration is above 12%
  • ethanol dissolves cell membrane
50
Q

what is the disadvantage of producing lactate in anaerobic respiration?

A

Acidic, so decreases pH
causes muscle fatigue

51
Q

compare anaerobic and aerobic respiration

A

Similarities
- Both involve glycolysis
- Both require NAD
- Both produce ATP
Differences
- aerobic produces ATP by substrate level phosphorylation and oxidative phosphorylation whereas anaerobic produces ATP by substrate level phosphorylation only
- aerobic produces more ATP than anaerobic
- aerobic does not produce lactate or ethanol whereas anaerobic does

A-Level Biology (8 decks)

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