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

Energy Transfers In and Between Organisms (Topic 5) Flashcards

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
Suggest how a student could investigate the effect of a named variable on the rate of photosynthesis.
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).
26
State the purpose and principle of paper chromatography.
Molecules in a mixture are separated based on their **relative attraction** to the mobile phase (**running solvent**) vs the stationary phase (**chromatography paper**).
27
Outline a method for extracting photosynthetic pigments.
Use a pestle and mortar to grind a leaf with an extraction solvent e.g. propanone.
28
Outline how paper chromatography can be used to separate photosynthetic pigments.
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.
29
What are Rf values? How can they be calculated?
• 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
30
Name the 4 main stages in aerobic respiration and where they occur.
**Glycolysis**: cytoplasm **Link reaction**: mitochondrial matrix **Krebs cycle**: mitochondrial matrix **Oxidative phosphorylation **via electron transfer chain: membrane of cristae
31
Outline the stages of glycolysis.
1. glucose is phosphorylated to glucose phosphate by 2x ATP 2. glucose phosphate splits into 2x triose phosphate (TP) 2. 2x TP is oxidised to 2x pyruvate Net gain of 2x reduced NAD & 2x ATP per glucose.
32
How does pyruvate from glycolysis enter the mitochondria?
Via active transport
33
What happens during the link reaction?
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**.
34
Give a summary equation for the link reaction.
pyruvate + NAD + CoA → acetyl CoA + reduced NAD + CO2
35
What happens in the Krebs cycle?
series of redox reactions produces: • ATP by substrate-level phosphorylation. • Reduced coenzymes. • CO2 from decarboxylation.
36
What is the electron transfer chain (ETC)?
Series of carrier proteins embedded in membrane of the cristae of mitochondria. Produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration.
37
What happens in the electron transfer chain (ETC)?
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.
38
How is a proton concentration gradient established during chemiosmosis in aerobic respiration?
Some **energy released from the ETC** is **coupled** to the **active transport** of **H + ions** (protons) from the **mitochondrial matrix into the intermembrane space**.
39
How does chemiosmosis produce ATP during aerobic respiration?
**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
State the role of oxygen in aerobic respiration.
Final electron acceptor in electron transfer chain. (produces water as a byproduct)
41
What is the benefit of an electron transfer chain rather than a single reaction?
• energy is released gradually • less energy is released as heat
42
Name 2 types of molecule that can be used as alternative respiratory substrates.
• (amino acids from) proteins • (glycerol and fatty acids from) lipids
43
How can lipids act as an alternative respiratory substrate?
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
How can amino acids act as an alternative respiratory substrate?
Deamination produces: 1. 3C compounds → pyruvate for link reaction. 2. 4C/ 5C compounds → intermediates in Krebs cycle.
45
Name the stages in respiration that produce ATP by substrate-level phosphorylation.
• Glycolysis (anaerobic) • Krebs cycle (aerobic)
46
What happens during anaerobic respiration in animals?
Only glycolysis continues reduced NAD + pyruvate → oxidised NAD (for further glycolysis) + lactate
47
What happens to the lactate produced in anaerobic respiration?
Transported to liver via bloodstream, where it is oxidised to pyruvate. Can enter link reaction in liver cells or be converted to glycogen.
48
What happens during anaerobic respiration in some microorganisms e.g. yeast and some plant cells?
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
What is the advantage of producing ethanol/ lactate during anaerobic respiration?
Converts reduced NAD back into NAD so glycolysis can continue.
50
What is the disadvantage of producing ethanol during anaerobic respiration?
• Cells die when ethanol concentration is above 12%. • Ethanol dissolves cell membranes.
51
What is the disadvantage of producing lactate during anaerobic respiration?
Acidic, so decreases pH. Results in muscle fatigue.
52
Compare aerobic and anaerobic respiration.
• Both involve glycolysis • Both require NAD • Both produce ATP
53
Contrast aerobic and anaerobic respiration.
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
Suggest how a student could investigate the effect of a named variable on the rate of respiration of a single-celled organism.
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
What is the purpose of sodium hydroxide solution in a respirometer set up to measure the rate of aerobic respiration?
Absorbs CO2 so that there is a net decrease in pressure as O2 is consumed.
56
How could a student calculate the rate of respiration using a respirometer?
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
How do plants use the sugars from photosynthesis?
• primarily as respiratory substrates • to synthesise other biological molecules e.g. cellulose
58
What is biomass?
Total dry mass of tissue or mass of carbon measured over a given time in a specific area.
59
Suggest the units for biomass.
• when an area is being sampled: gm-2 • when a volume (e.g. a pond) is being sampled: gm-3
60
How can the chemical energy store in dry mass be estimated?
Using calorimetry. Energy released = specific heat capacity of water x volume of water (cm3 ) x temperature increase of water.
61
Why is bomb calorimetry preferable to simple calorimetry?
Reduces heat loss to surroundings.
62
How could a student ensure that all water had been removed from a sample before weighing?
Heat the sample and reweigh it until the mass reading is constant.
63
Define gross primary production (GPP).
Total chemical energy in plant biomass within a given volume or area.
64
Define net primary productivity (NPP).
Total **chemical energy available** for plant **growth**, plant **reproduction** and energy transfer to **other trophic levels after respiratory losses**.
65
Give the mathematical relationship between GPP and NPP.
NPP = GPP - R where R represents respiratory losses
66
Why is most of the Sun’s energy not converted to organic matter?
• 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
How can the net production of consumers be calculated?
**N = I - (F + R)** I: chemical energy from ingested food F: energy lost as faeces and urine R: respiratory losses
68
Why does biomass decrease along a food chain?
• Energy lost in nitrogenous waste (urine) & faeces. • Some of the organism is not consumed. • Energy lost to surroundings as heat.
69
Define primary and secondary productivity.
• rate of primary or secondary production • biomass in a specific area over a given time period e.g. kJ ha^–1 year^–1
70
Outline some common farming practices used to increase the efficiency of energy transfer.
• 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
Give a general equation for % efficiency
energy converted to a useful form (J) x 100 / total energy supplied (J)
72
Explain why the length of food chains is limited.
Energy is lost at each trophic level So there is insufficient energy to support a higher trophic level
73
What is a pyramid of biomass?
Diagram that shows the biomass at each trophic level.
74
Why is a pyramid of biomass preferable to a pyramid of numbers?
Shape of pyramid of numbers may be skewed since a small number of producers can support many consumers.
75
Name the general stages in the phosphorus cycle.
1. Weathering 2. Runoff 3. Assimilation 4. Decomposition 5. Uplift
76
Why is the phosphorus cycle a slow process?
• Phosphorus has no gas phase, so there is no atmospheric cycle. • Most phosphorus is stored as PO4 3- in rocks.
77
What happens during weathering and runoff?
Phosphate compounds from sedimentary rocks leach into surface water and soil.
78
Explain the significance of phosphorus to living organisms.
Plants convert inorganic phosphate into biological molecules e.g. DNA, ATP, NADP… Phosphorus is passed to consumers via feeding.
79
What happens during uplift?
Sedimentary layers from oceans (formed by the bodies of aquatic organisms) are brought up to land over many years.
80
How does mining affect the phosphorus cycle?
Speeds up uplift.
81
Name the 4 main stages of the nitrogen cycle.
1. Nitrogen fixation 2. Ammonification 3. Nitrification 4. Denitrification
82
Why can’t organisms use nitrogen directly from the atmosphere?
N2 is very stable due to strong covalent triple bond.
83
What happens during atmospheric fixation of nitrogen?
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
Outline the role of bacteria in nitrogen fixation.
Mutualistic nitrogen-fixing bacteria in nodules of legumes & free-living bacteria in soil. Use the enzyme nitrogenase to reduce gaseous nitrogen into ammonia.
85
Outline the role of bacteria in ammonification.
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
Outline the role of bacteria in nitrification.
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
Outline the role of bacteria in denitrification.
Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen.
88
Explain the significance of nitrogen to living organisms.
Plant roots uptake nitrates via active transport & use them to make biological compounds e.g: • amino acids • NAD/ NADP • nucleic acids
89
Outline the role of mycorrhizae.
Mutualistic relationship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions.
90
Give 3 benefits of planting a different crop on the same field each year.
• 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
Name the 2 categories of fertiliser and state the purpose of using fertiliser.
• Organic: decaying organic matter & animal waste. • Inorganic: minerals from rocks, usually containing nitrogen, phosphorus, potassium. • To increase gross productivity for higher yield
92
At a certain point, using more fertiliser no longer increases crop yield. Why?
A factor unrelated to the concentration of mineral ions limits the rate of photosynthesis, so rate of growth cannot increase any further.
93
Outline 2 main environmental issues caused by the use of fertilisers.
1. **Leaching**: nitrates dissolve in rainwater and ‘runoff’ into water sources. 2.** Eutrophication**: water source becomes putrid as a result of algal bloom.
94
What happens during eutrophication?
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
How can the risk of eutrophication be reduced?
• Sewage treatment marshes on farms. • Pumping nutrient-enriched sediment out of water. • Using phosphate-free detergent.

Biology Revision (9 decks)

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