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Biology A-Level > Anaerobic Respiration incl. rice , Mitochondria + Respiratory Substrates (Chapter 12) > Flashcards

Anaerobic Respiration incl. rice , Mitochondria + Respiratory Substrates (Chapter 12) Flashcards

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1
Q

What happens when oxygen is not present?

A

1) hydrogen cannot be disposed of by combination with oxygen
2) ∴ the ETC stops working and no further ATP is formed by OP
3) the link reaction, Krebs cycle and OP do not take place (but glycolysis does)

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2
Q

What is necessary for a cell to gain even the 2 ATP for each glucose yielded by glycolysis?

A

To pass on the hydrogens from the molecules of reduced NAD that are made in glycolysis

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3
Q

What are the two different anaerobic pathways that solve the problem of ‘dumping’ the hydrogen?

A

Alcoholic and lactic

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4
Q

Where do both of the anaerobic pathways take place?

A

In the cytoplasm of the cell

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5
Q

What happens during alcoholic fermentation?

A

1) first, the pyruvate is decarboxylated to ethanal
2) then, the ethanal is reduced to ethanol (C2H5OH) by alcohol dehydrogenase
3) the H from reduced NAD is passed to ethanal (CH3CHO) when it forms ethanol
4) this releases the NAD and allows glycolysis to continue

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6
Q

Summarise alcoholic fermentation

A

Conversion of glucose to ethanol

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7
Q

In what microorganisms does alcoholic fermentation happen?

A

Yeast and in some plant tissues

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8
Q

What happens in during lactic fermentation?

A

1) pyruvate acts as the H acceptor and is converted to lactate by lactate dehydrogenase
2) again, the NAD is released and allows glycolysis to continue

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9
Q

Why does anaerobic respiration only buy time?

A

1) they allow the continued production of ATP even though oxygen is not available as the hydrogen accepter
2) however, bc the products of anaerobic respiration (ethanol/lactate) are toxic, these reactions cannot continue indefinitely

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10
Q

Can the alcoholic pathway be reversed?

A

No, ∴ the remaining chemical potential energy is wasted

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11
Q

How is the lactate pathway reversed in mammals?

A

1) most of the lactate is carried by the blood plasma to the liver and converted back into pyruvate
2) the liver oxidises some (20%) of the incoming lactate to CO2 and H2O via aerobic respiration when oxygen is available again
3) the remaining lactate is converted to glycogen by the liver

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12
Q

How does a person build up an oxygen deficit?

A

1) standing still, a person absorbs oxygen at a resting rate of 0.2 dm3/min
2) when exercise begins, more oxygen is needed to support aerobic respiration in the person’s muscles. increasing the overall demand to 2.5dm3/min
3) however, it takes 4 mins for the heart and lungs to meet the demand and during this time, lactic fermentation occurs in the muscles ∴ the person builds up an oxygen deficit
4) after this time, enough oxygen is supplied

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13
Q

What happens when exercise stops?

A

The person continues to breathe deeply and absorb oxygen at a higher rate than when at rest

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14
Q

What is the oxygen debt?

A

The post-exercise uptake of extra oxygen, which is paying back the oxygen deficit

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15
Q

What is the extra oxygen needed for post-exercise?

A

1) the conversion of lactate to glycogen in the liver
2) reoxygenation of haemoglobin in the blood
3) a high metabolic rate, as many organs are operating at above resting levels

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16
Q

What is the mitochondrion the site of in eukaryotic organisms?

A

The site of the Krebs cycle and the ETC

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17
Q

Describe the features of mitochondria

A
  • Rod-shaped or filamentous organelles
  • 0.5-1 µm in diameter
  • Not rigid and can change their shape
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18
Q

What does the number of mitochondria in a cell depend on?

A

The cell’s activity e.g. a liver cell has many mitochondria as it is very active

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19
Q

Describe the structure of mitochondria

A
  • Each mitochondrion is surrounded by an envelope of 2 phospholipid membranes (like chloroplast)
  • The outer membrane is smooth, but the inner membrane is very folded to give cristae
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20
Q

What do the cristae give the inner membrane?

A

A large total surface area

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21
Q

What do mitochondria from more active cells have?

A

Longer, more densely packed cristae than those from less active cells

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22
Q

What is the difference between the two membranes?

A

The outer membrane is relatively permeable to small molecules, whereas the inner membrane is less permeable

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23
Q

Describe the inner membrane

A
  • The inner membrane is studded with tiny spheres (9nm diameter) called stalked particles which are the enzyme ATP synthase and are attached to the inner membrane by stalks
  • The inner membrane is the site of the ETC and contains the proteins necessary for this
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24
Q

Why does the intermembrane space in a mitochondrion have a lower pH than the matrix?

A

Due to the protons that are released into the intermembrane space by the activity of the ETC

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25
Q

Describe the matrix of the mitochondrion

A
  • The site of the link reaction and the Krebs cycle ∴ has the enzymes needed for these reactions
  • Contains small (70s) ribosomes and several identical copies of looped mitochondrial DNA
26
Q

Where and how is ATP formed in mitochondria?

A
  • ATP is formed in the matrix by the activity of ATP synthase on the cristae
  • The energy for the production of ATP comes from the proton gradient between the intermembrane space and the matrix
27
Q

What is ATP produced in mitochondria used for?

A

All the energy-requiring reactions of the cell, both inside and outside the mitochondrion

28
Q

For what cells is glucose the essential respiratory substrate?

A

Neurones in the brain

29
Q

What can cells such as RBCs and lymphocytes also oxidise and how?

A
  • Lipids and amino acids
  • When lipids are respired, carbon atoms are removed in pairs (as acetyl CoA) from the fatty acid chains and fed into the Krebs cycle
  • When amino acids are respired, the C-H skeletons of amino acids are converted into pyruvate or acetyl CoA
30
Q

Where does most of the energy liberated in aerobic respiration come from and what does this mean?

A
  • From the oxidation of hydrogen to water when reduced NAD and reduced FAD are passed to the ETC
  • ∴ the greater the number of hydrogens in the structure of the substrate molecule, the greater the energy value because the hydrogens are used in ATP production in chemiosmosis
31
Q

Why do fatty acids have a greater energy density (energy value per unit mass) than carbohydrates or proteins?

A

Fatty acids have more hydrogens per molecule than carbohydrates or proteins

32
Q

How is the energy value of a substrate determined?

A

By burning a known mass of the substance in oxygen in a calorimeter - the energy liberated by oxidising the substrate can be determined from the rise in temperature of a known mass of water in the calorimeter

33
Q

What are the energy densities of lipids, proteins and carbohydrates in KJ/g?

A
  • Lipid = 39.4
  • Protein = 17.0
  • Carbohydrate = 15.8
34
Q

What is the respiratory quotient (RQ)?

A

Volume (mols) of CO2 given out in a unit time/volume (mols) of oxygen taken in in a unit time

35
Q

Why is the RQ of glucose 1?

A

6CO2/6O2 = 1

36
Q

What 2 things does measuring the RQ show?

A

1) what substrate is being used in respiration

2) whether or not anaerobic respiration is taking place

37
Q

What are the typic RQ values for carbohydrates, proteins and lipids?

A
  • Carbohydrate = 1.0
  • Protein = 0.9
  • Lipid = 0.7
38
Q

What is the equation of alcoholic fermentation and what does this mean for the RQ value of glucose respiring anaerobically?

A
  • C6H12O6 = 2C2H5OH + 2CO2
  • ∴ RQ = 2/0 = ∞
  • In reality, some respiration in the cell will be aerobic ∴ a small volume will be taken up and the RQ will be < ∞
  • So, high RQ values (>1) indicate that alcoholic fermentation is occurring
39
Q

Why can no RQ value be calculated for lactic fermentation?

A

Because no CO2 is produced: glucose = 2lactic acid

40
Q

Why is rice often grown in paddies (fields where the ground is intentionally flooded), even though it can grow in dry conditions?

A

Rice can tolerate growing in water, whereas most of the weeds that might compete with it are not able to do so

41
Q

Why can most plants not grow in deep water?

A

1) Bc their roots do not get enough oxygen, required for aerobic respiration, which provides ATP
2) If the leaves are submerged, photosynthesis cannot take place bc there is not enough CO2 available bc gases diffuse much more slowly in water than in air
3) the [dissolved O2 and CO2] in water are much lower than they are in air, esp in rice paddies, where the rich mud in which the rice roots are planted contains many microorganisms, many of which are aerobic and take oxygen from water

42
Q

How do some varieties of rice respond to flooding?

A
  • They grow taller - as the water rises around them, they keep growing upwards so that the top parts o their leaves and flower spikes are always held above water
  • This allows oxygen and CO2 to be exchanged through stomata on the leaves
43
Q

How are rice plants adapted to allow diffusion of gases?

A

1) the stems of rice plants contain loosely packed cells forming a tissue called aerenchyma
2) ∴ gases are able to diffuse through the aerenchyma to other parts of the plant, including those under water
3) air is also trapped in between the ridges of underwater leaves which have a hydrophobic, corrugated surface that holds a thin layer of air in contact with the leaf surface

44
Q

How are rice plants adapted to their cells in the submerged roots sometimes still having to use alcoholic fermentation?

A

1) although ethanol, which is toxic, builds up in the tissues, the cells in rice roots can tolerate much higher levels than most plants
2) they produce more alcohol dehydrogenase, which breaks down ethanol
3) this allows the plants to grow actively even when oxygen is scarce, using ATP produced by alcoholic fermentation

45
Q

How can oxygen uptake during respiration be measured?

A

Using a respirometer suitable for measuring the rate of oxygen consumption of seeds or small terrestrial invertebrates

46
Q

How can oxygen consumption in a unit time be measured using a respirometer?

A

1) CO2 produced in respiration is absorbed by a suitable chemical e.g. soda lime or a conc solution of KOH/NaOH
2) any decrease in the volume of air surrounding the organisms results from their oxygen consumption
3) ∴ oxygen consumption in a unit time can be measured by reading the manometer fluid against the scale
4) the rate at which the pressure falls is a measure of the rate at which the respiring tissue is taking up oxygen

47
Q

Why must the temperature of the surroundings be kept constant when using a respirometer

A

Changes in temp alter the volume of air in the apparatus ∴ the temp of the surroundings must be kept constant while the readings are taken e.g. by using a thermostatically controlled water bath

48
Q

Why is a control tube necessary when using a respirometer?

A

The presence of a control tube containing an equal volume of inert material to the volume of the organisms used helps to compensate for changes in the atmospheric pressure

49
Q

How can a graph be plotted of oxygen consumption against temperature?

A

Take measurements for oxygen consumption at a series of temperatures

50
Q

How can a respirometer be used to measure the RQ of an organism?

A

1) find the oxygen consumption of the organism at a particular temperature (in cm3/min)
2) set up the respirometer with the same organism at the same temperature but with no chemical to absorb CO2
3) the manometer scale will show whether the volumes of oxygen absorbed and CO2 produced are the same
4) when the volumes are the same, the level of the manometer fluid will not change and the RQ will = 1
5) when more CO2 is produced than oxygen absorbed, the scale will show an increase in the volume of air in the respirometer (in cm3/min)
6) when less CO2 is produced than oxygen absorbed, the volume of air in the respirometer will decrease (in cm3/min)

51
Q

How can you calculate the RQ of an organism when there is more CO2 produced than oxygen absorbed?

A

RQ = CO2/O2 - (oxygen consumption + increase in vol of air)/oxygen consumption

52
Q

How can you calculate the RQ of an organism when there is less CO2 produced than oxygen absorbed?

A

RQ = CO2/O2 - (oxygen consumption - decrease in vol of air)/oxygen consumption

53
Q

What is another way of investigating the rate of respiration of yeast?

A

Using a redox dye e.g. a solution of DCPIP or methylene blue (artificial hydrogen acceptors)

54
Q

How can redox dyes be used to investigate the rate of respiration of yeast?

A

1) these dyes do not damage cells ∴ they can be added to a suspension of yeast cells
2) when reduced, these blue dyes become colourless - the rate of change from blue to colourless is a measure of the rate of respiration of the yeast
3) this technique can be used to investigate the effect of various factors on yeast respiration e.g. temperature, substrate concentration or different substrates

55
Q

What is the matrix of the mitochondrion?

A

The space inside the mitochondrion

56
Q

What are the cristae?

A

Folds in the inner membrane where the electron transport reactions of aerobic respiration occur

57
Q

What cells have many mitochondria?

A

1) sperm - need to swim
2) muscle cells - to contract
3) intestinal cells - active transport of glucose

58
Q

What does pyruvate act as in lactic fermentation?

A

The electron acceptor by removing electrons from reduced NAD so that NAD is regenerated, allowing glycolysis to continue and ∴ produce ATP

59
Q

Why do you need to leave the respirometer for 5 mins?

A

To allow the organisms to acclimatise to the conditions

60
Q

What are control variables when using a respirometer?

A

1) mass of organisms
2) size of tube
3) temperature
4) keep in the dark

61
Q

Which anaerobic pathway is more energy efficient?

A

Lactic

62
Q

When does lactic fermentation happen?

A

When muscles are deprived of oxygen

Biology A-Level (44 decks)

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