Respiration (5)

Question 1

What are the four stages in aerobic respiration?

Answer 1

• Glycolysis
• Link reaction
• Krebs cycle
• Oxidative phosphorylation

Question 2

Where do each of the stages of aerobic respiration happen?

Answer 2

Glycolysis happens in the cytoplasm of cells while the rest happens in the mitochondria

Question 3

What are the first unit of respiration?

Answer 3

It is usually glucose but organisms can also break down other complex organic molecules to respire like fatty acids and amino acids

Question 3

What is the process of glycolysis?

Answer 3

Glycolysis occurs in the cytoplasm of the cells and involves splitting one molecule of glucose into two smaller molecules of pyruvate. This reaction does not require oxygen.

Question 3

What are the structures that make up a mitochondrion?

Answer 3

• outer mitochondrial membrane
• inner mitochondrial membrane
• cristae
• mitochondrial DNA
• ribosomes
• mitochondrial matrix

Question 4

What are the stages in glycolysis? (Phosphorylation and Oxidation)

Answer 4

1. glucose is phosphorylated into hexose biphosphate
2. hexose biphosphate is split into 2 x triose phosphate
3. Triose phosphate is oxidized to form two molecules of pyruvate

Question 5

What are the products of glycolysis?

Answer 5

• 2x pyruvate
• 2 reduced NAD
• net gain of 2 ATP

Question 6

What are the steps in the link reaction?

Answer 6

1. Pyruvate is decarboxylated- removed CO2
2. NAD becomes reduced by collecting hydrogen from the pyruvate to form acetate
3. Acetate combines with coenzyme A to form acetyl-coA
   (NO ATP is produced)

Question 7

How does pyruvate enter the matrix of the mitochondria before the link reaction?

Answer 7

They are actively transported into the mitochondria

Question 8

What are the steps in the Krebs Cycle?

Answer 8

1. Acetyl-coA enters the krebs cycle and loses coA to become an acetyl group
2. The acetyl group combines with oxoacetate to from citrate
3. Citrate is converted to a 5 carbon compound through dehydrogenation (NADH) and decarboxylation (CO2)
4. This 5 carbon compound also undergoes dehydrogenation (NADx2 and FADH2) and decarboxylation (CO2) and substrate level phosphorylation (ATP)
5. The formed oxaloacetate then combines with another acetyl group and the cycle is repeated

Question 9

What enzyme catalyzes the reaction between an acetyl group and oxaloacetate?

Answer 9

Citrate synthase

Question 10

What is oxidative phosphorylation in relation to respiration?

Answer 10

This is the process where the energy carried by electrons, from reduced coenzymes is used to make ATP. This process happens in the inner mitochondrial membrane and produces a lot of ATP.

Question 11

What are the steps in oxidative phosphorylation?

Answer 11

1. hydrogen atoms are released from the reduced coenzymes and then split into H+ ions and electrons 2. The electrons move along the electron transport chain- losing energy at each carrier
2. The energy provided by the electrons is used to pump H+ ions from the matrix into the intermembrane space
3. As the concentration of H+ ions is higher in the intermembrane space than the matrix it form an electrochemical gradient
4. H+ ions move down this gradient back into the matrix through channels/ATP Synthesase which causes phosphorylation of ADP into ATP
5. At the end in the matrix the H+, O2 and electrons combine to form water

Question 12

What is the electron transport chain?

Answer 12

The electron transport chain happens in the inner mitochondrial membrane. It is where electrons lose energy as they are passed between carriers.

Question 13

Why is the inner mitochondrial membrane folded into cristae?

Answer 13

This increases the membrane’s surface area to maximize respiration.

Question 14

What is chemiosmosis?

Answer 14

Chemiosmosis is the process when H+ ions move down the electrochemical gradient through ATP synthesase which produces ATP

Question 15

What is oxygen referred to in the stage of oxidative phosphorylation?

Answer 15

It is referred to as the final electron acceptor

Question 16

How much ATP can one cell make from one molecule of glucose?

Answer 16

32 ATP

Question 17

What is different about anaerobic respiration and aerobic respiration?

Answer 17

Anaerobic respiration doesn’t involve the link reaction, the Krebs cycle or oxidative phosphorylation as it does not require oxygen

Question 18

What are the two types of anaerobic respiration?

Answer 18

Alcoholic fermentation and lactate fermentation

Question 19

How are aerobic and anaerobic respiration similar?

Answer 19

They both start with glycolysis and take place in the cytoplasm

Question 20

What is different between anaerobic and aerobic respiration?

Answer 20

They differ in which organisms they occur in and what happens to the pyruvate

Question 21

What is lactate fermentation?

Answer 21

Reduced NAD transfers hydrogen to pyruvate to form lactate and NAD. The NAD can then be reused in glycolysis

Question 22

Why can glycolysis continue when there isn’t much oxygen around?

Answer 22

The production of lactate regenerates NAD and glycolysis needs NAD to take place.

Question 23

Why do humans only respire anaerobically for short periods of time?

Answer 23

Our cells can tolerate a high level of lactate/low pH conditions for short periods of time e.g during hard exercise when they cannot get enough ATP from aerobic respiration

Question 24

Why can humans not have a lot of lactate present?

Answer 24

Too much lactate is toxic and is removed from the cells into the bloodstream. The liver takes up the lactate from the bloodstream and converts it back to glucose in a process called gluconeogenesis

Question 25

What are the steps in alcoholic fermentation?

Answer 25

1. CO2 is removed from pyruvate to form ethanal 2. Reduced NAD (from glycolysis) transfers hydrogen to ethanal to form ethanol and NAD 3. NAD can then be reused in glycolysis

Question 26

Why does anaerobic respiration release less energy than aerobic respiration?

Answer 26

- ATP yield is always lower in anaerobic than aerobic respiration because anaerobic respiration only includes one energy-releasing stage which only produces 2 ATP molecules. The Krebs cycle and oxidative phosphorylation need oxygen so they don't happen during anaerobic respiration.

Question 27

What other substances can cells respire?

Answer 27

Cells respire glucose but they can also respire other carbohydrates, lipids, and proteins. Any biological molecule that can be broken down in respiration to release energy is called a respiritory substrate.

Question 28

What is the order of energy released from respiratory substrates?

Answer 28

- The highest is lipids - proteins - The lowest is carbohydrates

Question 29

Why do lipids produce more ATP/energy than carbohydrates?

Answer 29

They contain more hydrogen atoms per unit of mass so more ATP can be formed in oxidative phosphorylation

Question 30

What is the respiritory quotient?

Answer 30

This is the volume of carbon dioxide produced when the substrate is respired, divided by the volume of oxygen consumed in a set period of time.

Question 31

Why is the respiritory quotient for an organism useful?

Answer 31

This is useful because it tells you what kind of respiratory substrate an organism is respiring and what type of respiration it is using

Question 32

What do high respiratory quotients mean?

Answer 32

It means that the organism is short of oxygen and is having to respire anaerobically as well as aerobically

Question 33

What do low respiratory quotients mean?

Answer 33

Plants sometimes have a low RQ. This is because the CO2 released in respiration is used for photosynthesis so it is not measured.

Question 34

How would you conduct an experiment to measure aerobic respiration in yeast?

Answer 34

1. add a known volume and concentration of glucose into a test tube 2. add a known volume of buffer solution 3. place test tube in a water bath at 25 to ensure the temperature stays constant- leave for at least 10 mins 4. add a known mass of dried yeast and stir for two minutes 5. when the yeast is dissolved add a bung attached to a gas syringe set to 0 6. start a stopwatch as soon as the bung is put in 7. measure the volume in the syringe per minuite or at regular time intervals 8. make sure to repeat the experiment and use a control

Question 35

How would you conduct an experiment to measure anaerobic respiration?

Answer 35

1. set up the apparatus the same as the aerobic experiment 2. after the yeast has dissolved add some liquid paraffin to create a layer above the yeast and glucose solution 3. measure the volume in the gas syringe at regular time intervals

Question 36

How can you measure the rate of respiration?

Answer 36

Use a respirometer

Question 37

How would you use a respirometer to measure the respiration rate of small organisms?

Answer 37

1. set up the apparatus 2. put soda lime in each test tube to absorb CO2 3. One tube has the small organism on a gauze and the other has beads of the same mass as the small organism 4. Add colored fluid to the manometer and use a syringe to set the fluid to a known level 5. Leave the apparatus for a set period of time 6. the decrease in the volume of air used by the small organism will cause a change in level in the manometer so read the distance moved in a period of time to measure the volume of oxygen taken in per minute 7. to make the results more precise repeat multiple times and calculate a mean