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A- Level Biology > unit 5 > Flashcards

unit 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

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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4
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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5
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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6
Q

Name the 3 main stages in the Calvin cycle

A
  1. Carbon fixation
  2. Reduction
  3. Regeneration
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7
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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8
Q

Describe the structure of a chloroplast 5

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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9
Q

How does the structure of the chloroplast
maximise the rate of the light-dependent
reaction? LDR

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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10
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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11
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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12
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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13
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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14
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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15
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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16
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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17
Q

How does pyruvate from glycolysis enter the mitochondria?

A

via active transport

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18
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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19
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

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20
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

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21
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.

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22
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

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23
Q

What happens during anaerobic respiration in animals?

A

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

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24
Q

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

A

Converts reduced NAD back into NAD
so glycolysis can continue

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25
Q

What is the disadvantage of producing
ethanol during anaerobic respiration?

A

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

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26
Q

What is the disadvantage of producing lactate during anaerobic respiration?

A

Acidic, so decreases pH.
Results in muscle fatigue.

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27
Q

Compare aerobic and anaerobic respiration 3

A

● Both involve glycolysis
● Both require NAD
● Both produce ATP

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28
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

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29
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
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30
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.

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31
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

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32
Q

How do plants use the sugars from
photosynthesis?

A

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

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33
Q

What is biomass?

A

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

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

34
Q

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

A

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

35
Q

Why is bomb calorimetry preferable to simple calorimetry?

A

Reduces heat loss to surroundings.

36
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.

37
Q

Define
-Gross primary production GPP
-Net primary production

npp=gpp-r

A

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

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

38
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/

39
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

39
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

40
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

41
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

42
Q
A
43
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.

44
Q

Name the general stages in the
phosphorus cycle.

A
  1. Weathering
  2. Runoff
  3. Assimilation
  4. Decomposition
  5. Uplift
45
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.

46
Q

What happens during weathering and runoff?

A

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

47
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

48
Q

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

A

N2
is very stable due to strong covalent
triple bond

49
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-
50
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

51
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
    +
52
Q

Outline the role of bacteria in denitrification.

A

Anaerobic denitrifying bacteria convert
soil nitrates back into gaseous nitrogen.

53
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

54
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.

55
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

56
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

57
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

58
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.
59
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.

60
Q

how farming practices increases crop productivity

A

-Fertilisers containing nitrates added to soil
-Nitrates used for proteins and phosphate for ATP
-Selective breeding of crops
-Ploughing decreases denitrification
-Crop rotation allows higher crop yields by having different nutrients and different pests

61
Q

nitrogen fixing bacteria increase growth of plants

A

-nitrogen fixing bacteria convert
-nitrogen in the air into ammonium compounds which are converted to nitrates
-plants use nitrates for amino acids

61
Q

why is nitrates entering freshwater bad

A

-increased concentrations of nitrates cause rapid growth of algae
-algal bloom blocks light
reduced photosynthesis so plants die
-saprobionts aerobically respire
-less oxygen for fish to respire so they die

62
Q

how microorganisms in soils produce a source a source of nitrates:

A

-amino acids / DNA assimilates into ammonium compounds
-by saprobionts
-ammonium converted to nitrile
-nitrile converted to nitrates by nitrification
-by nitrifying bacteria

63
Q

Glycolysis:

A

1.Glucose is phosphorylated 2x using 2.ATP to produce 2x Triose Phosphate
3.ATP hydrolysed to ADP + Pi
4.NAD is reduced to reduced NAD (NADH)
5.2x Triose phosphate is oxidised to 2x pyruvate

64
Q

Phosphorous cycle:

A

1.PO43- released by rocks into the soil due to weathering/erosion
2.Plants absorb these phosphate ions
3.Animals eat + digest these plants and use these ions to synthesise organic matter
4.Excess PO43- are excreted by animals
5.On death, decomposers) break these animals down releasing PO43- to water & soil
6.PO43- found in bones/shells, but slow release
7.Some PO43- is transported by streams / lakes where they form sedimentary rocks

65
Q

leaching:

A

Process by which nutrients are removed from the soil
Find their way into watercourses (streams, rivers)
Can have a harmful effect on humans if the lake is a source of drinking water

66
Q

link reaction:

A

1.Pyruvate moves into the matrix
decarboxylation of pyruvate, CO2 released
2.NAD reduced to form NADH
3.Pyruvate oxidised to Acetate
4.Acetate combines with CoEnzyme A to form Acetyl CoA

67
Q

Kreb’s cycle:
6

A
  1. Acetyl CoA combines with 4 Carbon compound to form 6 carbon compound releases Coenzyme A
  2. 6C converted to 5C
  3. decarboxylation and hydrogen removed by NAD to produce reduced NAD;
  4. 5C converted to 4C
  5. decarboxylation and hydrogen removed by NAD/FAD to produce reduced NAD/FAD;
  6. ATP produced through substrate level phosphorylation
68
Q

recall what happens in oxidative phosphorylation: 6

A

1.(absorption of light causes ) Electrons to be released from NADH and FADH
2.electrons move down the electron transport chain releasing energy. This energy is used to actively transport protons into the intermembrane space
3.establishes a chemiosmotic gradient
4.H+ move by facilitated diffusion through ATP synthase back into matrix
5.resulting in the formation of ATP: ADP + inorganic phosphate => ATP
6.Oxygen is the final electron acceptor
protons, electrons and oxygen to form H2O

69
Q

Recall what happens to pyruvate in anaerobic conditions and explain why this is advantageous to humans:

A
  1. Reduced to lactate;
  2. Using reduced NAD;
  3. Regenerates NAD;
  4. NAD can be reused to allow glycolysis to continue;
  5. Can still release energy/form ATP when oxygen in short supply
70
Q

ethanol fermentation pathway for anaerobic respiration:

A

Pyruvate is decarboxylated to ethanal
Ethanal reduced to ethanol by enzyme alcohol dehydrogenase
NADH transfers its H to ethanal, which is a H acceptor

70
Q

how aerobic respiration stops functioning in the absence of oxygen:

A
  • No final acceptor of electrons in ETC
    -ETC stops functioning
    -No more ATP via OxPhosp
    -NADH, FADH not oxidised by electron carrier (e- arent moving along)
    -No oxidised NAD+/FAD+ available for Krebs’s
    -Krebs’s stops
71
Q

why is less ATP produced in anaerobic respiration:
)

A

no electron transport chain/ oxidative phosphorylation
this is one which produces majority of ATP
only glycolysis occurs (net 2 ATP per glucose

72
Q

explain photoionisation and chemiosmosis:

A

Photoionisation of chlorophyll causes an electron to become excited
the electron travels down the electron transport chain emitting energy as it goes down which is used to pump H+ across the thylakoid membrane.
H+ diffuses out of the thylakoid membrane through ATP synthase, which provide energy for and ADP + inorganic phosphate molecule to form ATP

73
Q

how light wavelength affects rate of photosynthesis:

A

-Light needs to be at a particular wavelength (leaves look green because they reflect green light` - they absorb blue + red)
-Different pigments absorb different wavelengths

74
Q

how light intensity affects rate of photosynthesis:

A

-More energy for photoionisation in the L.D.R; hence faster rate of photosynthesis
-If low, LDR is slower. ATP and NADPH not produced, hence conversion of GP into TP will be slower. GP will rise (still being made) and TP + RUBP will fall (used to make GP)

75
Q

explain how temperature affects rate of photosynthesis:

A

-calvin cycle is controlled by enzymes (e.g. rubisco)
at low temperatures, slower enzyme reactions as enzyme works more slowly
-Levels of RuBP, GP and TP will fall
increasing temp. increases rate to optimum; beyond optimum, rate decreases

76
Q

how is NADPH formed:

A

-photoionisation of chlorophyll causes photolysis
-water molecule is split into protons, electrons and oxygen molecules
-oxygen diffuses out of the chloroplast -via the stomata
-H+ reduce NADP to produces reduced NADP (NADPH)

77
Q

Calvin cycle, Light independent reaction:

A

1.Carbon dioxide enters the leaf and diffuses into the stroma
2.CO2 combines with Ribulose bisphosphate producing 2 molecules of glycerate-3-phosphate
3.Catalysed by the enzyme rubisco
4.Glycerate-3-phosphate is reduced to 2 molecules of triose phosphate
5.Using reduced NADP (NADPH –> NADP)
6.Using energy from ATP
7.1/6 of triose phosphate is converted to hexose sugE and other useful organic substances
8.5/6 of triose phosphate is recycled to generate ribulose bisphosphate

78
Q

light-dependent reaction:

1.chlorophyll absorbs light energy
2.Excites electrons in chlorophyll.
3.Electrons move along the electron transport chain releasing energy.
4.This energy is used to pump H+ across the thylakoid membrane by facilitated diffusion creating a chemiosmotic gradient
5.H+ diffuse out through ATP synthase, providing energy for ATP synthesis
6.Energy is used to join ADP +Pi–> ATP
7.Photolysis of water produces protons, electrons and oxygen
8.NADP is reduced by electrons

A
79
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.

A- Level Biology (9 decks)

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