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Biology Revision > Energy Transfers In and Between Organisms (Topic 5) > Flashcards

Energy Transfers In and Between Organisms (Topic 5) Flashcards

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1
Q

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

A

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

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2
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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3
Q

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

A
  1. electron transfer chain
  2. chemiosmosis
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4
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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5
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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6
Q

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

A

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

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7
Q

Explain the role of light in photolysis.

A

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

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8
Q

What happens to the products of the
photolysis of water?

A

•** H
+
ions**: move out of thylakoid 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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9
Q

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

A

• NADP + 2H+
+ 2e-
→ reduced NADP.
• Catalysed by dehydrogenase
enzymes.
• Stroma of chloroplasts.

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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
transfer 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
& ribulose
bisphosphate (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

• 2 x GP are reduced to 2 x triose
phosphate (TP)
• Requires 2 x reduced NADP & 2 x ATP
• Forms 2 x NADP & 2 x 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 (i.e. some of the TP
is converted into useful organic
molecules).

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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 & (reduced) NADP
in the light-independent reaction.

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.

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17
Q

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

A

RuBP: 5
GP: 3
TP: 3

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18
Q

Describe the structure of a chloroplast.

A

• Usually disc-shaped.
• Double membrane (envelope).
• Thylakoids: flattened discs stack to form grana.
• Intergranal lamellae: 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 area 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 & ribosomes for synthesis of
enzymes e.g. rubisco.
• Concentration of enzymes &
substrates in stroma is high.

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21
Q

Define ‘limiting factor’.

A

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

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22
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).

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23
Q

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

A

• Artificial light, especially at night.
• Artificial heating.
• Addition of CO2
to greenhouse
atmosphere.

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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.

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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 hydrogencarbonate indicator (colour change
orange → magenta as CO2
is consumed & pH
increases).

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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).

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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.

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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) 1 cm 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.
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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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30
Q

Name the 4 main stages in aerobic
respiration and where they occur.

A

Glycolysis: cytoplasm
Link reaction: mitochondrial matrix
Krebs cycle: mitochondrial matrix
**Oxidative phosphorylation **via electron transfer
chain: membrane of cristae

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31
Q

Outline the stages of glycolysis.

A
  1. glucose is phosphorylated to glucose phosphate
    by 2x ATP
  2. glucose phosphate splits into 2x triose phosphate
    (TP)
  3. 2x TP is oxidised to 2x pyruvate
    Net gain of 2x reduced NAD & 2x ATP per glucose.
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32
Q

How does pyruvate from glycolysis enter
the mitochondria?

A

Via active transport

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33
Q

What happens during the link reaction?

A
  1. Oxidation of pyruvate to acetate.
    Per pyruvate molecule: net gain of 1xCO2
    (decarboxylation) & 2H atoms (used to reduce
    1xNAD    ).
  2. Acetate combines with coenzyme A (CoA) to
    form acetylcoenzyme A.
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34
Q

Give a summary equation for the link
reaction.

A

pyruvate + NAD + CoA
→
acetyl CoA + reduced NAD + CO2

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35
Q

What happens in the Krebs cycle?

A

series of redox reactions produces:
• ATP by substrate-level
phosphorylation.
• Reduced coenzymes.
• CO2
from decarboxylation.

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36
Q

What is the electron transfer chain
(ETC)?

A

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

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37
Q

What happens in the electron transfer
chain (ETC)?

A

Electrons released from reduced NAD & FAD
undergo successive redox reactions.
The energy released is coupled to
maintaining proton gradient or released as
heat.
Oxygen acts as final electron acceptor.

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38
Q

How is a proton concentration gradient
established during chemiosmosis in
aerobic respiration?

A

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

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39
Q

How does chemiosmosis produce ATP
during aerobic respiration?

A

H
+
ions (protons) move down their
concentration gradient from the
intermembrane space into the mitochondrial
matrix via the channel protein ATP synthase.
ATP synthase catalyses ADP + Pi → ATP.

40
Q

State the role of oxygen in aerobic
respiration.

A

Final electron acceptor in electron
transfer chain.
(produces water as a byproduct)

41
Q

What is the benefit of an electron
transfer chain rather than a single
reaction?

A

• energy is released gradually
• less energy is released as heat

42
Q

Name 2 types of molecule that can be
used as alternative respiratory
substrates.

A

• (amino acids from) proteins
• (glycerol and fatty acids from) lipids

43
Q

How can lipids act as an alternative
respiratory substrate?

A

lipid → glycerol + fatty acids
1. Phosphorylation of glycerol → TP for glycolysis.
2. Fatty acid → acetate.
a) acetate enters link reaction.
b) H atoms produced for oxidative phosphorylation.

44
Q

How can amino acids act as an
alternative respiratory substrate?

A

Deamination produces:
1. 3C compounds → pyruvate for link reaction.
2. 4C/ 5C compounds → intermediates in
Krebs cycle.

45
Q

Name the stages in respiration that
produce ATP by substrate-level
phosphorylation.

A

• Glycolysis (anaerobic)
• Krebs cycle (aerobic)

46
Q

What happens during anaerobic
respiration in animals?

A

Only glycolysis continues
reduced NAD + pyruvate
→
oxidised NAD (for further
glycolysis) + lactate

47
Q

What happens to the lactate produced in
anaerobic respiration?

A

Transported to liver via bloodstream,
where it is oxidised to pyruvate.
Can enter link reaction in liver cells or be
converted to glycogen.

48
Q

What happens during anaerobic
respiration in some microorganisms e.g.
yeast and some plant cells?

A

Only glycolysis continues.
Pyruvate is decarboxylated to form ethanal.
Ethanal is reduced to ethanol using reduced
NAD to produce oxidised NAD for further
glycolysis.

49
Q

What is the advantage of producing
ethanol/ lactate during anaerobic
respiration?

A

Converts reduced NAD back into NAD
so glycolysis can continue.

50
Q

What is the disadvantage of producing
ethanol during anaerobic respiration?

A

• Cells die when ethanol concentration
is above 12%.
• Ethanol dissolves cell membranes.

51
Q

What is the disadvantage of producing
lactate during anaerobic respiration?

A

Acidic, so decreases pH.
Results in muscle fatigue.

52
Q

Compare aerobic and anaerobic
respiration.

A

• Both involve glycolysis
• Both require NAD
• Both produce ATP

53
Q

Contrast aerobic and anaerobic
respiration.

A

Aerobic
• produces ATP by
substrate-level phosphorylation
AND oxidative phosphorylation
• produces much more ATP
• does not produce ethanol or
lactate
Anaerobic
• substrate-level
phosphorylation only
• produces fewer ATP
• produces ethanol or
lactate

54
Q

Suggest how a student could investigate
the effect of a named variable on the rate
of respiration of a single-celled organism.

A
  1. Use respirometer (pressure changes in
    boiling tube cause a drop of coloured
    liquid to move).
  2. Use a dye as the terminal electron
    acceptor for the ETC.
55
Q

What is the purpose of sodium hydroxide
solution in a respirometer set up to
measure the rate of aerobic respiration?

A

Absorbs CO2 so that there is a net
decrease in pressure as O2
is
consumed.

56
Q

How could a student calculate the rate of
respiration using a respirometer?

A

Volume of O2
produced or CO2 consumed/
time x mass of sample
Volume = distance moved by coloured
drop x (0.5 x capillary tube diameter)2
x π

57
Q

How do plants use the sugars from
photosynthesis?

A

• primarily as respiratory substrates
• to synthesise other biological
molecules e.g. cellulose

58
Q

What is biomass?

A

Total dry mass of tissue or mass of
carbon measured over a given time in a
specific area.

59
Q

Suggest the units for biomass.

A

• when an area is being sampled: gm-2
• when a volume (e.g. a pond) is being
sampled: gm-3

60
Q

How can the chemical energy store in
dry mass be estimated?

A

Using calorimetry.
Energy released = specific heat capacity
of water x volume of water (cm3
) x
temperature increase of water.

61
Q

Why is bomb calorimetry preferable to
simple calorimetry?

A

Reduces heat loss to surroundings.

62
Q

How could a student ensure that all
water had been removed from a sample
before weighing?

A

Heat the sample and reweigh it until the
mass reading is constant.

63
Q

Define gross primary production (GPP).

A

Total chemical energy in plant biomass
within a given volume or area.

64
Q

Define net primary productivity (NPP).

A

Total chemical energy available for
plant growth, plant reproduction and
energy transfer to other trophic levels
after respiratory losses.

65
Q

Give the mathematical relationship
between GPP and NPP.

A

NPP = GPP - R
where R represents respiratory losses

66
Q

Why is most of the Sun’s energy not
converted to organic matter?

A

• Most solar energy is absorbed by atmosphere or
reflected by clouds.
• Photosynthetic pigments cannot absorb some
wavelengths of light.
• Not all light falls directly on a chlorophyll molecule.
• Energy lost as heat during respiration/ photosynthesis.

67
Q

How can the net production of
consumers be calculated?

A

N = I - (F + R)
I: chemical energy from ingested food
F: energy lost as faeces and urine
R: respiratory losses

68
Q

Why does biomass decrease along a
food chain?

A

• Energy lost in nitrogenous waste (urine)
& faeces.
• Some of the organism is not consumed.
• Energy lost to surroundings as heat.

69
Q

Define primary and secondary
productivity.

A

• rate of primary or secondary
production
• biomass in a specific area over a given
time period e.g. kJ ha^–1 year^–1

70
Q

Outline some common farming practices
used to increase the efficiency of energy
transfer.

A

• Exclusion of predators: no energy lost to other
organisms in food web.
• Artificial heating: reduce energy lost to maintain
constant body temperature.
• Restriction of movement.
• Feeding is controlled at the optimum.

71
Q

Give a general equation for % efficiency

A

energy converted to a useful form (J) x 100
/
total energy supplied (J)

72
Q

Explain why the length of food chains is
limited.

A

Energy is lost at each trophic level
So there is insufficient energy to support
a higher trophic level

73
Q

What is a pyramid of biomass?

A

Diagram that shows the biomass at each
trophic level.

74
Q

Why is a pyramid of biomass preferable
to a pyramid of numbers?

A

Shape of pyramid of numbers may be
skewed since a small number of
producers can support many consumers.

75
Q

Name the general stages in the
phosphorus cycle.

A
  1. Weathering
  2. Runoff
  3. Assimilation
  4. Decomposition
  5. Uplift
76
Q

Why is the phosphorus cycle a slow
process?

A

• Phosphorus has no gas phase, so
there is no atmospheric cycle.
• Most phosphorus is stored as PO4
3- in
rocks.

77
Q

What happens during weathering and
runoff?

A

Phosphate compounds from sedimentary
rocks leach into surface water and soil.

78
Q

Explain the significance of phosphorus to
living organisms.

A

Plants convert inorganic phosphate into
biological molecules e.g. DNA, ATP, NADP…
Phosphorus is passed to consumers via
feeding.

79
Q

What happens during uplift?

A

Sedimentary layers from oceans (formed
by the bodies of aquatic organisms) are
brought up to land over many years.

80
Q

How does mining affect the phosphorus
cycle?

A

Speeds up uplift.

81
Q

Name the 4 main stages of the nitrogen
cycle.

A
  1. Nitrogen fixation
  2. Ammonification
  3. Nitrification
  4. Denitrification
82
Q

Why can’t organisms use nitrogen
directly from the atmosphere?

A

N2
is very stable due to strong covalent
triple bond.

83
Q

What happens during atmospheric
fixation of nitrogen?

A
  1. High energy of lightning breaks N2
    into
    N.
  2. ## N reacts with oxygen to form NO2.
  3. ## NO2^dissolves in water to form NO3^
    -
    .
84
Q

Outline the role of bacteria in nitrogen
fixation.

A

Mutualistic nitrogen-fixing bacteria in
nodules of legumes & free-living bacteria
in soil.
Use the enzyme nitrogenase to reduce
gaseous nitrogen into ammonia.

85
Q

Outline the role of bacteria in
ammonification.

A
  1. Saprobionts feed on and decompose
    organic waste containing nitrogen (e.g.
    urea, proteins, nucleic acids…).
  2. NH3
    released.
  3. NH3
    dissolves in water in soil to form
    NH4^
    +
    .
86
Q

Outline the role of bacteria in nitrification.

A

Outline the role of bacteria in nitrification.
2-step process carried out by
saprobionts in aerobic conditions:
2NH4^
+
+ 3O2
→ 2NO2^
-
+ 2H2O + 4H^+
2NO2^
-
+ O2
→ 2NO3^-

87
Q

Outline the role of bacteria in
denitrification.

A

Anaerobic denitrifying bacteria convert
soil nitrates back into gaseous nitrogen.

88
Q

Explain the significance of nitrogen to
living organisms.

A

Plant roots uptake nitrates via active transport &
use them to make biological compounds e.g:
• amino acids
• NAD/ NADP
• nucleic acids

89
Q

Outline the role of mycorrhizae.

A

Mutualistic relationship between plant
and fungus increases surface area of
root system = increases uptake of water
and mineral ions.

90
Q

Give 3 benefits of planting a different
crop on the same field each year.

A

• Nitrogen-fixing crops e.g. legumes make soil
more fertile by increasing soil nitrate content.
• Different crops have different pathogens.
• Different crops use different proportions of
certain ions.

91
Q

Name the 2 categories of fertiliser and
state the purpose of using fertiliser.

A

• Organic: decaying organic matter & animal
waste.
• Inorganic: minerals from rocks, usually
containing nitrogen, phosphorus, potassium.
• To increase gross productivity for higher yield

92
Q

At a certain point, using more fertiliser no
longer increases crop yield. Why?

A

A factor unrelated to the concentration of
mineral ions limits the rate of
photosynthesis, so rate of growth cannot
increase any further.

93
Q

Outline 2 main environmental issues
caused by the use of fertilisers.

A
  1. Leaching: nitrates dissolve in rainwater
    and ‘runoff’ into water sources.
    2.** Eutrophication**: water source becomes
    putrid as a result of algal bloom.
94
Q

What happens during eutrophication?

A
  1. Aquatic plants grow exponentially since nitrate level is no
    longer a limiting factor.
  2. Algal bloom on water surface prevents light from
    reaching the bottom and plants die.
  3. Oxygen levels decrease as population of aerobic
    saprobionts increases to decay dead matter, so fish die.
  4. Anaerobic organisms reproduce exponentially and
    produce toxic waste which makes water putrid.
95
Q

How can the risk of eutrophication be
reduced?

A

• Sewage treatment marshes on farms.
• Pumping nutrient-enriched sediment
out of water.
• Using phosphate-free detergent.

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