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

Question 1

What happens when oxygen is not present?

Answer 1

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)

Question 2

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

Answer 2

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

Question 3

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

Answer 3

Alcoholic and lactic

Question 4

Where do both of the anaerobic pathways take place?

Answer 4

In the cytoplasm of the cell

Question 5

What happens during alcoholic fermentation?

Answer 5

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

Question 6

Summarise alcoholic fermentation

Answer 6

Conversion of glucose to ethanol

Question 7

In what microorganisms does alcoholic fermentation happen?

Answer 7

Yeast and in some plant tissues

Question 8

What happens in during lactic fermentation?

Answer 8

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

Question 9

Why does anaerobic respiration only buy time?

Answer 9

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

Question 10

Can the alcoholic pathway be reversed?

Answer 10

No, ∴ the remaining chemical potential energy is wasted

Question 11

How is the lactate pathway reversed in mammals?

Answer 11

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

Question 12

How does a person build up an oxygen deficit?

Answer 12

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

Question 13

What happens when exercise stops?

Answer 13

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

Question 14

What is the oxygen debt?

Answer 14

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

Question 15

What is the extra oxygen needed for post-exercise?

Answer 15

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

Question 16

What is the mitochondrion the site of in eukaryotic organisms?

Answer 16

The site of the Krebs cycle and the ETC

Question 17

Describe the features of mitochondria

Answer 17

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

Question 18

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

Answer 18

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

Question 19

Describe the structure of mitochondria

Answer 19

• 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

Question 20

What do the cristae give the inner membrane?

Answer 20

A large total surface area

Question 21

What do mitochondria from more active cells have?

Answer 21

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

Question 22

What is the difference between the two membranes?

Answer 22

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

Question 23

Describe the inner membrane

Answer 23

• 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

Question 24

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

Answer 24

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

Question 25

Describe the matrix of the mitochondrion

Answer 25

• 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

Question 26

Where and how is ATP formed in mitochondria?

Answer 26

• 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

Question 27

What is ATP produced in mitochondria used for?

Answer 27

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

Question 28

For what cells is glucose the essential respiratory substrate?

Answer 28

Neurones in the brain

Question 29

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

Answer 29

• 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

Question 30

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

Answer 30

• 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

Question 31

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

Answer 31

Fatty acids have more hydrogens per molecule than carbohydrates or proteins

Question 32

How is the energy value of a substrate determined?

Answer 32

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

Question 33

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

Answer 33

• Lipid = 39.4
• Protein = 17.0
• Carbohydrate = 15.8

Question 34

What is the respiratory quotient (RQ)?

Answer 34

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

Question 35

Why is the RQ of glucose 1?

Answer 35

6CO2/6O2 = 1

Question 36

What 2 things does measuring the RQ show?

Answer 36

1) what substrate is being used in respiration

2) whether or not anaerobic respiration is taking place

Question 37

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

Answer 37

• Carbohydrate = 1.0
• Protein = 0.9
• Lipid = 0.7

Question 38

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

Answer 38

• 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

Question 39

Why can no RQ value be calculated for lactic fermentation?

Answer 39

Because no CO2 is produced: glucose = 2lactic acid

Question 40

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

Answer 40

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

Question 41

Why can most plants not grow in deep water?

Answer 41

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

Question 42

How do some varieties of rice respond to flooding?

Answer 42

• 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

Question 43

How are rice plants adapted to allow diffusion of gases?

Answer 43

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

Question 44

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

Answer 44

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

Question 45

How can oxygen uptake during respiration be measured?

Answer 45

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

Question 46

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

Answer 46

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

Question 47

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

Answer 47

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

Question 48

Why is a control tube necessary when using a respirometer?

Answer 48

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

Question 49

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

Answer 49

Take measurements for oxygen consumption at a series of temperatures

Question 50

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

Answer 50

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)

Question 51

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

Answer 51

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

Question 52

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

Answer 52

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

Question 53

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

Answer 53

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

Question 54

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

Answer 54

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

Question 55

What is the matrix of the mitochondrion?

Answer 55

The space inside the mitochondrion

Question 56

What are the cristae?

Answer 56

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

Question 57

What cells have many mitochondria?

Answer 57

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

Question 58

What does pyruvate act as in lactic fermentation?

Answer 58

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

Question 59

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

Answer 59

To allow the organisms to acclimatise to the conditions

Question 60

What are control variables when using a respirometer?

Answer 60

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

Question 61

Which anaerobic pathway is more energy efficient?

Answer 61

Lactic

Question 62

When does lactic fermentation happen?

Answer 62

When muscles are deprived of oxygen