5.2.2 Respiration

Question 1

Why do organisms need to respire ?

Answer 1

It provides ATP as energy for the following purposes :
•Active transport of substances against a concentration gradient
•Metabolic reactions e.g. to form peptide bonds
•Muscle contractions

Question 2

Describe the structure of a mitochondrion

Answer 2

•Surrounded by a double membrane
•Folded inner membrane forms cristae ; this is the site of the electron transport chain
•A fluid matrix, this contains mitochondrial DNA, enzymes and bio-molecules.

Question 3

Name the four main stages in aerobic respiration and where they occur

Answer 3

•Glycolysis : cytoplasm
•Link reaction : mitochondrial matrix
•Krebs cycle : mitochondrial matrix
•Oxidative phosphorylation : membrane of cristae.

Question 4

Outline the stages of glycolysis and the net molecule change

Answer 4

1. Glucose is phosphorylated to hexose bisphosphate by 2 ATP
2. Hexose bisphosphate splits into 2 triose phosphate
3. These two triose phosphate is oxidised to 2 pyruvate (via NAD)

•There is a net gain of 2 reduced NAD and 2 ATP per glucose

Question 5

How does a pyruvate from glycolysis enter the mitochondria ?

Answer 5

Via active transport

Question 6

What happens during the link reaction ?

Answer 6

1. Oxidation of pyruvate to acetate (via NAD). This causers a loss of 1 CO2 and 2H per pyruvate
2. Acetate combines with coenzyme A to form Acetylcoenzme A.

Question 7

What happens in the Krebs cycle ?

Answer 7

See sheet

Question 8

Outline the stages of the Krebs cycle

Answer 8

See sheet

Question 9

What is the electron transfer chain ?

Answer 9

•A series of carrier proteins imbedded in the membrane of the cristae of the mitochondria
•It produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration.

Question 10

What happens in the electron transfer chain ?

Answer 10

•Electrons reduced from reduced NAD & FAD undergo successive redox reaction
•The energy released is coupled to maintain proton gradients / some heat energy
•Oxygen acts as the final electron acceptor.

Question 11

How does chemiosmosis produce ATP during aerobic respiration ?

Answer 11

•Some energy released from the ETC is coupled to active transport H+ ions from mitochondrial matrix into the intermembrabe space
•H+ ions move down concentration gradients into the mitochondrial matrix via the ATP synthase channel protein
•ATP synthase catalyses ADP + Pi -> ATP

Question 12

State the role of oxygen in aerobic respiration

Answer 12

•It’s the final electron acceptor in electron transfer chain
•This produces H2O as a byproduct.

Question 13

Name the stages in respiration that produce ATP by substrate level phosphorylation

Answer 13

•Glycolysis (anaerobic)
•Krebs cycle (aerobic)

Question 14

What happens during anaerobic respiration in animals ?

Answer 14

•Only glycolysis continues
•rNAD + Pyruvate -> NAD + Lactate.

Question 15

What happens in anaerobic respiration in yeast ?
(Biology)

Answer 15

•Only glycolysis continues, so much less ATP is produced compared to aerobic respiration
•Pyruvate is decarboxylised to form ethanal
•Ethanal is reduced into ethanol using rNAD -> NAD.

Question 16

What are the benefits to being able to respire anaerobically ?

Answer 16

•ATP production for vital metabolic processes continues even in oxygen deprived conditions
•Production of ethanol/lactate converts rNAD into NAD so glycolysis can continue.

Question 17

Suggest how a student could investigate the effect of a given variable on the rate of respiration of a single celled organism ?

Answer 17

•Use a respirometer, pressure changed in a boiling tube will cause dyed liquid to move)
•Use a dye as the final electron acceptor for the ETC.

Question 18

What is the purpose of the NaOH solution in a respirometer ?

Answer 18

It absorbs CO2 so that there is a net decrease in pressure as O2 is consumed

Question 19

How could a student calculate the rate of respiration using results from a respirometer ?

Answer 19

Volume of O2 produced or CO2 consumed x mass of sample

Question 20

Name two types of molecule that can be used as alternative respiratory substrates

Answer 20

•Amino acids
•Glycerol / fatty acids

Question 21

What is the respiratory quotient (RQ)

Answer 21

RQ = CO2 produced / O2 consumed
It can be used to determine :
•The respiratory substrate being used (Carb = 1.0, protein = 0.9, lipids = 0.8)
•If the organism is undergoing anaerobic respiration (RQ will be >1).

Question 22

Why do different respiratory substrates have different energy values ?

Answer 22

•It depends on the number of hydrogen atoms in the molecule as these are oxidised into water
•For example there are more H in fatty acids than carbohydrates.