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A Level Biology AQA > 5. Energy Transfer In & Between Organisms > Flashcards

5. Energy Transfer In & Between Organisms Flashcards

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1
Q

General adaptations of the leaf for photosynthesis

A
  • Large SA to absorb as much light as possible
  • Arrangement of leaves to minimise overlapping (avoids shading)
  • Transparent cuticle & epidermis to let light through to the mesophyll cells below
  • Long narrow upper mesophyll cells packed with chloroplasts to collect sunlight
  • Many air spaces in lower mesophyll layer for rapid diffusion in the (g) phase of co2 and h2O
  • Network of xylem to carry h2O to leaf cells and phloem to carry sugars produced away
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2
Q

What is the overall equation for photosynthesis

A

6CO2 + 6H2O ———> C6H12O6 + 6O2
. light

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3
Q

What are the 3 main stages to photosynthesis

A
  1. Capturing of light energy (chlorophyll)
  2. Light-dependant reaction (splitting of water)
  3. Light independent reaction (reduction of co2)
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4
Q

What are the 2 purposes for the energy from the capture of light in the LD reaction of photosynthesis

A
  • to add an inorganic phosphate (Pi) molecule to ADP making ATP. Process known as photophosphorylation
  • to split water into H+ ions (protons) and OH- ions. Process known as photolysis
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5
Q

Explain briefly how ATP is made (photosynthesis: LD stage)

A

Chlorophyll molecule absorbs light = energy of pair of electrons is boosted= they move to a higher energy level
Results in chlorophyll molecule becoming ionised (photoionisation)
Electrons are taken up and passed along a number of electron carriers (forms a transfer chain) in a series of oxidation&reduction reactions
Each new carrier is at a slightly lower energy level so the electrons lose energy
Some of this energy is used to combine Pi with ADP to make ATP

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6
Q

Which theory describes and explains the precise mechanism by which ATP is produced in the LD reaction?

A

Chemiosmotic theory

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7
Q

Step by step process of the mechanism for the production of ATP in the LD stage (chemiosmotic theory)

A
  • Protons are pumped from the stroma into each thylakoid using proton pumps in the thylakoid membrane
  • Photolysis of water also produces protons which increases their conc inside the thylakoid space
  • A conc gradient is created & maintained across the thylakoid membrane (high conc of protons inside thylakoid space, low conc in stroma)
  • Protons pass through ATP synthase protein channels and as they do cause changes to the structure of the enzyme which then catalyses the combination of ADP with Pi to form ATP
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8
Q

Where does the energy used to drive the process of pumping protons into the thylakoids come from

A

Energy from electrons released when water molecules are split by light (photolysis)

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9
Q

Why is the photolysis of water necessary

A

Loss of electrons when light strikes chlorophyll molecule leaves it short of electrons. If the chlorophyll molecule is to continue absorbing light energy, these electrons must be replaced.
Replacement electrons are provided from photolysis
Protons are also produced

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10
Q

What is the equation for photolysis of water

A

2H2O ———> 4H+ + 4e- + O2

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11
Q

Describe and explain the role of protons produced from the photolysis of water (LD stage)

A
  • Protons are passed out of the thylakoid space through ATP synthase channels and are taken up by an electron carrier called NADP
  • By taking up the protons NADP becomes reduced. (Allows transport of hydrogen into light independant reaction)
  • The reduced NADP is important because it is a further potential source of chemical energy to the plant.
  • The oxygen by-product is either used for respiration or diffuses out of the leaf as a waste product of photosynthesis
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12
Q

How are chloroplasts structurally adapted for capturing sunlight and carrying out the LD reaction of photosynthesis

A
  • Thylakoid membranes provide a large SA for attachment of chrlophyll, electron carriers and enzymes used in the LD reaction
  • Network of proteins in grana hold chlorophyll in a precise manner for max absorption of light
  • Granal membranes have ATP synthase channels within them and are selectively permeable which allows proton gradient to be established
  • Chloroplasts contain both DNA & ribosomes so they can quickly & easily manufacture some of the proteins involved in the LD reaction
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13
Q

What are the products of the LD reaction (ATP and reduced NADP) used for in the second stage of photosynthesis?

A

To reduce glycerate 3-phosphate

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14
Q

What does the Calvin cycle refer to

A

The second stage of photosynthesis : Light independent reaction that takes place within the stroma of the chloroplasts

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15
Q

Give the step by step process of the Calvin cycle

A
  • CO2 reacts with the 5 carbon compound ribulose biphosphate (RuBP), a reaction catalysed by an enzyme known as rubisco
  • This reaction produces two molecules of the 3-carbon, glycerate 3-phosphate (GP)
  • Reduced NADP, produced in the LD reaction, is used to reduce GP to triose phosphate (TP) using energy supplied by ATP
    - The NADP is re-formed and returned to the LD reaction to be reduced again by accepting more protons
  • Some TP molecules are converted to organic substances that the plant needs (eg. starch cellulose lipids glucose amino acids & nucleotides)
  • Most TP molecules are used to regenerate ribulose bisphosphate using ATP from the LD reaction
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16
Q

How is the chloroplast adapted to carry out the LID reaction of photosynthesis

A
  • fluid of stroma contains all enzymes needed to carry out the LID reaction.
  • The stroma fluid surrounds the grana so the products of the LD reaction in the grana can readily diffuse into the stroma
  • Contains both DNA & ribosomes so it can quickly & easily manufacture some of the proteins involved in the LID reaction
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17
Q

Define the law of limiting factors

A

At any given moment the rate of physiological process is limited by the factor that is at its least favourable value

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18
Q

What does compensation point mean

A

The point at which the volume of o2 produced & co2 absorbed in photosynthesis is exactly balanced by the o2 absorbed & co2 produced by cellular respiration

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19
Q

What is the effect of temperature on the rate of photosynthesis

A

Provided that other factors are not limiting, the rate of photosynthesis increases in direct proportion to the temperature
Above optimum temperature, the rate falls steeply

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20
Q

How does CO2 concentration affect the rate of photosynthesis

A

No photosynthesis at very low levels
At low - fairly low concentrations, the rate is positively correlated with CO2
At very high concentrations the rate reaches a plateau
CO2 affects enzyme activity, in particular the enzyme that catalyses the combination of ribulose bisphosphate with co2 in the LID reaction

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21
Q

How does light intensity affect the rate of photosynthesis 

A

At low – medium light intensities, the rate is directly proportional to light intensity
At high light intensity the rate reaches a plateau

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22
Q

What are the 2 different forms of cellular respiration ?

A

Aerobic respiration
Anaerobic respiration

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23
Q

What 4 stages make up aerobic respiration ?
Where do they take place ?

A

Glycolysis - cytoplasm
Link reaction - mitochondrial matrix
Kerbs cycle - mitochondrial matrix
Oxidative phosphorylation - inner mitochondrial membrane

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24
Q

Describe in simple terms what happens in glycolysis

A

The splitting of the 6-carbon glucose molecules into x2 3-carbon pyruvate molecules

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25
Q

Describe in simple terms what happens in the link reaction

A

The 3-carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetylcoenzyme A, a 2-carbon molecule

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26
Q

Describe in simple terms what happens in the Krebs cycle

A

The introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of NADH & FADH

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27
Q

Describe in simple terms what happens in oxidative phosphorylation

A

The use of the electrons, associated with NADH & FADH, released from the Krebs cycle, to synthesise ATP. Water is produced as a by-product

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28
Q

Give the step by step process of glycolysis

A
  1. Glucose is phosphorylated to glucose phosphate. Phosphate molecules come from the hydrolysis of x2 ATP molecules to ADP
  2. Each glucose phosphate is split into x2 triose phosphate molecules
  3. Oxidation of triose phosphate. Hydrogen is removed and transferred to NAD to form NADH
  4. Production of ATP. Enzyme controlled reactions convert each triose phosphate into a pyruvate molecule. Each time x2 ATP is regenerated from ADP
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29
Q

What is the overall yield from one molecule of glucose undergoing glycolysis ?

A
  • x2 ATP
  • x2 NADH
  • x2 molecules of pyruvate
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30
Q

Give the step by step process of the link reaction

A
  1. Pyruvate molecules produced in the cytoplasm during glycolysis are actively transported into the mitochondrial matrix
  2. Pyruvate is oxidised to acetate. Loses x1 co2 and x2 hydrogens. Hydrogens are accepted by NAD to form NADH
  3. The acetate combines with coenzyme A (CoA) to produce acetylcoenzymeA
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31
Q

Give the step by step process of the Krebs Cycle

A
  1. The 2-carbon acetylcoenzymeA from the link reaction combines with a 4-carbon molecule to form a 6-carbon molecule
  2. In a series of reactions this molecule loses co2 and hydrogen to give a 4-carbon molecule, NADH, FADH and x1 ATP produced as a result of substrate level phosphorylation
  3. The 4-carbon molecule can now combine with a new molecule of acetylcoenzymeA and the cycle can begin again
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32
Q

What is the yield of both the link reaction and Krebs cycle ?

A
  • reduced coenzymes such as NAD and FAD
  • one molecule of ATP
  • x3 molecules of co2

As there are x2 pyruvate molecules produced for each single glucose molecule the yield is double the quantities above

33
Q

What are coenzymes

A

Molecules that some enzymes require in order to function

34
Q

Give the step by step process of oxidative phosphorylation.

A
  1. The hydrogen atoms produced during glycolysis & the Krebs cycle combine with the coenzymes NAD & FAD
  2. NADH & FADH donate the electrons of the hydrogen atoms they’re carrying to the first molecule in the electron transfer chain
  3. The electrons pass down the electron transfer chain in a series of oxidation-reduction reactions.
  4. The energy they release allows for the active transport of protons across the inner mitochondrial membrane and into the inter-membrane space
  5. Protons accumulate in the inter-membrane space before they diffuse back into the mitochondrial matrix through ATP synthase channels
  6. At the end of the chain the electrons combine with these protons & oxygen to form water
35
Q

What is the importance of oxygen in respiration ?

A

Act as the final acceptor of the hydrogen atoms produced in glycolysis and the Krebs cycle.
Without it the hydrogen ions (protons) and electrons would back up along the chain and the process of respiration would halt

36
Q

What are the 2 alternative respiratory substrates

A

Lipids and proteins

37
Q

How does respiration using lipids as a substrate work?

A

Lipids are first hydrolysed to glycerol and fatty acids.
Glycerol is then phosphorylated and converted to triose phosphate which enters through the glycolysis pathway
The fatty acid component is broken down into 2-carbon fragments which are converted to acetylcoenzyme A which enters the Krebs cycle
Many hydrogen atoms are also produced and used to produce ATP during oxidative phosphorylation

38
Q

How does respiration using proteins as a substrate work ?

A

First hydrolysed to its constituent amino acids.
They have their amino group removed before entering the respiratory pathway at different points depending on the amount of carbon atoms they contain

39
Q

In eukaryotic cells, what are the two types of anaerobic respiration that occur with any regularity ?

A
  • In plants and in microorganisms such as yeast, pyruvate is converted to ethanol and to co2
  • In animals, the pyruvate is converted to lactate
40
Q

Give the summary equation for anaerobic respiration in plants and some microorganisms

A

Pyruvate + NADH —> ethanol + co2 + oxidised NAD

41
Q

Why must anaerobic respiration be used during periods of strenuous activity

A

Energy demand is high
Oxygen is being used up quicker than it can be supplied (oxygen debt occurs)

42
Q

What is the role of the pyruvate molecules in anaerobic respiration

A

When oxygen is in short supply, NADH from glycolysis can accumulate and must be removed.
The pyruvate molecule takes up the two hydrogen atoms from the reduced NAD to form lactate
NAD is recycled

43
Q

Give the summary equation for anaerobic respiration in animals

A

Pyruvate + NADH —-> lactate + oxidised NAD

44
Q

Why does a person often breathe deeply for a few mins after strenuous exercise

A

Anaerobic respiration produces lactate which must be broken down by oxygen in aerobic respiration

45
Q

When oxygen is available again what happens to the lactate

A

Oxidised back to pyruvate, further oxidised to release energy
If o2 isn’t available it’s removed by the blood and taken to the liver where it’s converted to glycogen

46
Q

What does lactate cause if it accumulates in the muscle tissue

A

Cramp and muscle fatigue
As it is acidic it also causes pH changes which affects enzymes

47
Q

Define producers

A

Photosynthetic organisms that manufacture organic substances using light energy, water co2 and mineral ions

48
Q

Define consumers

A

Organisms that obtain their energy by feeding on (consuming) other organisms rather than using energy from the sunlight directly.
Primary, secondary or tertiary

49
Q

Define saprobionts

A

Group of organisms that break down the complex minerals in dead organisms into simple ones.
In doing so they release valuable minerals & elements in a form that can be absorbed by plants and so contribute to recycling

50
Q

Define food chain

A

Describes the feeding relationship in which producers are eaten by primary consumers, which are then eaten by secondary consumers etc.

51
Q

What is each stage in the food chain referred to as

A

Trophic level

52
Q

What do they arrows in a food chain represent

A

The direction of energy flow

53
Q

Define biomass

A

The total mass of living material in a specific area at a given time

54
Q

Why does the volume of water in living organisms cause issues when calculating biomass?
What do we use instead as a result ?

A

Volume of water varies so makes measuring biomass unreliable
Instead we measure the mass of carbon or dry mass

55
Q

What are the disadvantages of using dry mass or mass of carbon to calculate biomass?

A

Involves killing an organism which means only small samples can be measured which are not representative

56
Q

How can bomb calorimetry be used to estimate the chemical energy store in biomass

A

Sample of biomass is weighed and burnt in pure oxygen within a sealed chamber (bomb)
Bomb is surrounded by a known vol of water and the heat of combustion causes temp to rise.
Temp rise is measured and used to calc energy released from mass of burnt biomass

57
Q

Why can plants only capture 1-3% of the light energy from the sun ?

A
  • over 90% of the sun’s energy is reflected back into space by clouds/dust or is absorbed by the atmosphere
  • not all wavelengths of light can be absorbed and used for photosynthesis
  • light may not fall on a chlorophyll molecule
  • a factor, such as low co2 levels, may limit rate of photosynthesis
58
Q

How do you calculate net primary production

A

net primary production = gross primary production - respiratory losses

59
Q

Why is so little energy transferred between each trophic level ?

A
  • some of the organism isn’t consumed
  • some parts consumed can’t be digested and are therefore lost in faeces
  • some is lost in excretory materials eg. Urine
  • some us lost as heat from respiration
60
Q

How do we calculate the net production of consumers

A

N = I - (F + R)

N : net production
I : chemical energy store of injected food
F : energy lost in faeces and urine
R : energy lost in respiration

61
Q

How do we calculate the efficiency of energy transfers

A

energy available after the transfer
————————————————- x100
Energy available before the transfer

62
Q

How does intensive farming increase the energy conversion rate ?

A
  • movement is restricted and so less energy is used in muscle contraction
  • environment can be kept warm to reduce heat loss from body
  • feeding can be controlled so animals receive optimum amount and type of food for maximum growth (no wastage)
  • predators are excluded so there is no loss to other organisms in the food web
63
Q

What are the 4 main stages of the nitrogen cycle?

A

Ammonification
Nitrification
Nitrogen fixation
Denitrification

64
Q

Ammonification is:

A

Production of ammonia from organic nitrogen containing compounds (urea, protein, nucleic acids, vitamins)
Saprobiontic microorganisms feed on faeces/dead organisms releasing ammonia, leading to the formation of ammonium ions in the soil

65
Q

Nitrification:

A

Some bacteria obtain their energy from chemical reactions involving inorganic ions
1 example is the conversion of ammonium ions to nitrate ions carried out by nitrifying bacteria that occurs in 2 stages:
- oxidation of ammonium ions to nitrite ions (NO2-)
- oxidation of nitrite ions to nitrate ions (NO3-)

66
Q

Why is it important for farmers to plough and drain fields

A

Nitrifying bacteria require oxygen for the 2 step conversion reaction of ammonium ions to nitrate ions.
Therefore, to raise productivity farmers plough to keep soil structure light & well aerated.
Good drainage also prevents air spaces from being filled with water and so prevents air being forced out of the soil.

67
Q

Nitrogen fixation:

A

Process by which nitrogen gas is converted to nitrogen containing compounds
Carried out by 2 main types of organisms:
- free living nitrogen fixing bacteria
- mutualistic nitrogen fixing bacteria

68
Q

Describe and explain the role of free-living nitrogen-fixing bacteria

A

These bacteria reduce gaseous nitrogen to ammonia, which they then use to manufacture amino acids.
When they die and decay, they release nitrogen-rich compounds

69
Q

Describe and explain the role of mutualistic nitrogen-fixing bacteria

A

These bacteria live in nodules on the roots of plants.
They obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria

70
Q

Denitrification:

A

When soils become waterlogged and have low o2 conc, the type of microorganism present changes.
Increase in anaerobic denitrifying bacteria which convert soil nitrates into gaseous nitrogen which reduces the availability of nitrogen-containing compounds for plants

71
Q

What does the phosphorus cycle lack that both the nitrogen and carbon cycle have?

A

A gaseous phase

72
Q

Describe and explain the main reservoir of the phosphorus cycle

A

Phosphorus exists mostly as phosphate ions in the form of sedimentary rock deposits
Weathering and erosion of these rocks help phosphate ions to become dissolved and ready for absorption by plants which incorporate them into their biomass

73
Q

Describe the and explain the role of mycorrhizae in nutrient cycles

A

mycorrhizae are associates between certain types of fungi and the roots of the vast majority of plants. (Mutualistic relationship)
The fungi increase the surface area for absorption of water and minerals by acting as extensions of the root system of plants
The mycorrhiza acts like a sponge so holds water and minerals in the neighbourhood of roots which enables the plant to better resist drought and to take up inorganic ions more easily

74
Q

Why do we need fertilisers?

A

In natural ecosystems the minerals that are removed from the soil by plants are returned when the plant is decomposed by microorganisms on its death.
In agricultural systems, concentrations of mineral ions will fall as when the crop is harvested and transported for consumption, the remains of the consumer are rarely returned to the same area of land.
Reduced concentrations of mineral ions will become the main limiting factor to plant growth, resulting in reduced productivity

75
Q

What are the 2 types of fertilisers ?

A

Natural (organic) fertilisers : consist of dead and decaying remains of plants and animals as well as animal waste
Artificial (inorganic) fertilisers : mined from rocks and deposits, then converted into different forms and blended together to give appropriate balance of minerals for the crop

76
Q

What are the 3 negative effects of nitrogen containing fertilisers

A

Reduced species diversity
Leaching
Eutrophication

77
Q

How do nitrogen containing fertilisers reduce species diversity

A

Nitrogen rich soils favour the growth of grasses, nettles etc
These outcompete many other species which die as a result

78
Q

How do nitrogen containing fertilisers cause leaching

A

Rainwater dissolves any soluble nutrients such as nitrate ions and carry them deep into the soil, beyond the reach of plant roots
The leached nitrate ions find their way into watercourses that may in turn drain into freshwater lakes.
Here, they may have a harmful effect on humans if the river/ lake is a source of drinking water or on the environment (eutrophication)

79
Q

Give the sequence of events of eutrophication

A
  1. In most lakes/rivers conc of nitrate is naturally low so nitrate ions are a limiting factor for agal & plant growth
  2. Due to leaching nitrate conc increases, ceasing to become a limiting factor in agal & plant growth
  3. The upper layers of water become densely populated with algae (algal bloom)
  4. This dense layer absorbs light and prevents it from penetrating lower depths
  5. Light becomes the limiting factor for growth of plants & algae at lower depths, so they eventually die
  6. Populations of saprobiontic bacteria grow as the lack of dead plants & algae is no longer a limiting factor
  7. These bacteria require oxygen for respiration, increasing the demand for it
  8. Oxygen conc in the water is reduced and nitrates are released form decaying organisms
  9. Oxygen becomes the limiting factor for the pop. of aerobic organisms which ultimately die
  10. Without the aerobic organisms there is less competition for anaerobic organisms, whose populations now rise
  11. Anaerobic organisms further decompose dead material releasing nitrates & some toxic wastes

A Level Biology AQA (9 decks)

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