Respiration

Question 1

Order of the four stages of aerobic respiration and location

Answer 1

Glycolysis (cytoplasm), the link reaction (matrix), the krebs cycle (matrix) and oxidative phosphorylation (inner mitochondrial membrane)

Question 2

Glycolyses

Answer 2

Glucose is phosphorylated using ATP to form fructose phosphate, this lowers the activation energy of the raction. It is then further phosphorylated using another ATP molecule to form fructose bisphosphate. This breaks down to form two molecules of TP (triose phosphate). Hydrogen is removed from TP and reduces two molecules of NAD. This turns TP into Pyruvate.

Question 3

What are the products of glycolyses

Answer 3

2 molecules of reduced NAD, 2 molecules of Pyruvate and 4 molecules of ATP.

Question 4

The link reaction

Answer 4

When oxygen is available pyruvate is decarboxylated (CO2 is removed), dehydrogenated (H2 is removed). It is then combined with coenzyme A to give acetyl coenzyme A (2C). The hydrogen removed is used to reduce NAD

Question 5

The krebs cycle

Answer 5

Acetyl coenzyme A combines with a four carbon compound (oxaloacetate) to form citrate (6C). The citrate is decarboxylated and dehydrogenated to yield CO2 (a waste product) and hydrogen which reduces NAD and FAD to form reduced NAD and reduced FAD. Oxaloacetate is regenerated to combine with another acetyl coenzyme A.

Question 6

Products of the krebs cycle

Answer 6

2 CO2 molecules, one reduced FAD molecule, 3 reduced NAD molecules and one ATP molecule.

Question 7

Oxidative phosphorylation

Answer 7

The hydrogen carriers reduced NAD and reduced FAD are oxidised and release hydrogen which is split into electrons and H+. The electrons are transferred to the electron transport chain. As electrons pass through the chain, they lose energy – which is used by the chain to pump protons (H+ ions) from the matrix. The accumulation of H+ ions within the intermembrane space creates an electrochemical gradient . Protons pass back into the matrix down the concentration gradient through proton channels. Associated with each channel is the enzyme ATP synthase, as the protons pass through ATP is synthesised by chemiosmosis. Oxygen acts as the final electron acceptor, removing the electrons to prevent the chain from becoming blocked. Oxygen also binds with protons in the matrix to form water – removing matrix protons maintains the hydrogen gradient. In the absence of oxygen, hydrogen carriers cannot transfer energised electrons to the chain and ATP production is halted

Question 8

Different ways ATP is produced in the mitochondria

Answer 8

It is synthesised in substrate-linked reactions in glycolyses and the krebs cycle. The synthesis of ATP is associated with the electron transport chain on the membranes of mitochondria and chloroplasts.

Question 9

Outline the roles of the coenzyme NAD, FAD and coenzyme A in respiration

Answer 9

They act as electron carriers moving electrons between molecules. For example, they transport hydrogen to the electron transport chain where they can be split into hydrogen ions and electrons. When the coenzymes are reduced it gives the electrons more energy for the electron carrier chain. Coenzyme A carrys ethanoate (acetate) groups, made from pyruvate during the link reaction, onto Krebs cycle

Question 10

Mitochondrial structure and function

Answer 10

They are rod shaped and are 0.5-1.0 micrometers in diameter. There are more mitochondria in more metabolically active organs such as the liver. Surrounded by an envelope of two phospholipid membranes. The inner membrane is folded to form cristae, these increase the surface area. Mitochondria from more active cells have longer, more densely packed cristae. The outer membrane is permeable to small molecules, whereas the inner membrane is less permeable. The inner membrane is studded with spheres which are ATP synthase. The inner membrane has the proteins necessary for the electron transport chain. The marix contains the enzymes necessary for the krebs cycle and link reaction. The ATP produced in the mitochondria can be used for the energy requiring processes of the mitochondria. The inner membrane space has a low ph which helps with the production of ATP as the protons create a proton gradient.

Question 11

Why does anaerobic respiration take place

Answer 11

When no oxygen is available, hydrogen can not be disposed off by combining with oxygen. The electron transport chain strops working and no further ATP is formed by oxidative phosphorylation. Anaerobic respiration therefore allows some ATP to be produced when there is not enough oxygen present.

Question 12

Alcoholic fermentation

Answer 12

Occurs in yeast and some plant tissue. Pyruvate is decarboxylated to ethanal, ethanal is reduced to ethanol by the enzyme alcohol dehydrogenase, using two hydrogen atoms from reduced NAD. This release the NAD and allows glycolyses to continue

Question 13

Lactic fermentation

Answer 13

Occurs in microorganisms and mammalian tissue deprived of oxygen. Pyruvate is reduced to lactate by the enzyme lactate dehydrogenase, using 2 hydrogen atoms from reduced NAD.

Question 14

Disadvantages of anaerobic respiration

Answer 14

Less ATP is produced. Ethanol and lactate are toxic so it cannot go on indefinitely. Ethanol cannot be converted back so is wasted.

Question 15

Oxygen deficiency

Answer 15

When someone is exercising their lungs cant keep up with the oxygen needs of their body and they have oxygen defecit. When they stop exercising they continue to breathe deeply and absorb oxygen at a higher rate then at rest. This post exercise uptake of oxygen is paying back the oxygen defecit and is called oxygen debt.

Question 16

Oxygen debt

Answer 16

The extra oxygen is needed for; conversion of lactate to glycogen in the liver, reoxygenation of haemoglobin in the blood, a higher metabolic rate as many organs are operating at above resting levels.

Question 17

Energy value of respiratory substrate

Answer 17

A respiratory substrate is a molecule from which energy can be liberated to produce ATP in a living cell. Most of the energy released in respiration comes from the oxidation of hydrogen to water. The more hydrogens there are (in comparison with carbon or oxygen atoms) in the structure of a molecule, the greater the energy value. Fatty acids have more hydrogens per unit mass than carbohydrates, so lipids have a greater energy value per unit mass, then protein, then carbohydrate. The energy value of a substrate can be determined by using a calorimeter.

Question 18

Respiratory quotient

Answer 18

It is possible to get a good idea of which respiratory substrate the cells in an organism are using by measuring the volume of oxygen it is taking in and the volume of carbon dioxide it is giving out. As the ratio between oxygen consumed and CO2 eliminated differs between respiratory substrate. RQ = CO2 eliminated/O2 consumed.

Question 19

Respirometer

Answer 19

Sodium hydroxide absorbs all CO2 from the air in the apparatus from the beginning. As the germinating seeds use oxygen and the pressure reduces in tube A so the manometer level nearest to the seeds rises. Any CO2 excreted is absorbed by the sodium hydroxide solution.
The syringe is used to return the manometer fluid levels to normal. The volume of oxygen used is calculated by measuring the volume of gas needed from the syringe to return the levels to the original values. Temperature and pressure must remain constant, this can be done by using a thermostatically controlled water bath. The presence of a control tube containing an equal volume of inert material as the volume of the organism helps compensate for changes in atmospheric pressure.

Question 20

Calculating RQ using a respirometer

Answer 20

Set up two respirometers however, the second respirometer should also contain the same mass of live maggots (or whatever organism you are investigating) but should not contain soda lime. You could put some inert material into the tube (for example, the beads) instead of soda lime. The mass and volume of the inert material should be the same as the mass and volume of the soda lime. The carbon dioxide given out by the respiring organisms is therefore not absorbed. The difference between the distance moved by the manometer fluid in the experimental tube and the distance moved in the control tube is therefore due to the carbon dioxide given out. X is distance moved by experimental tube, Y is distance moved by control tube.
RQ = X-Y
———-
X

Question 21

Investigating factors that effect respiration

Answer 21

Use a respirometer and change temperature or substrate concentration

Question 22

Another way to investigate respiration

Answer 22

Using DCPIP or methlyn blue. The rate of change from blue to colourless is a measure of the rate of respiration.

Question 23

Rice adaptions

Answer 23

Some varieties of rice grow taller in flooded water so that their leaves are above water, so gases can be exchanged through the stomata. The stems of rice plant contain loosely packed aerenchyma, gases are able to diffuse through the aerenchyma to other parts of the plant, even those under water. The leaves have a hydrophobic corrugated surface which holds a thin layer of air in contact with the leaf surface. Rice roots have a much higher tolerance for the ethanol produced in anaerobic respiration then most plants. They also produce more alcohol dehydrogenase which breaks down ethanol, meaning they can have a high level of anaerobic respiration.