2.8/8.2 - cell respiration

Question 1

define cell respiration

Answer 1

the controlled release of energy from organic compounds to produce ATP

Question 2

why do all cells require a continuous supply of ATP?

Answer 2

• it is not transferred from cell to cell
• when energy from ATP is used in cells, it is ultimately all converted to heat. this cannot be reused for cell activities and is eventually lost to the environment

Question 3

three main activities that cells require energy for

Answer 3

• synthesising large molecules like DNA, RNA, and proteins
• pumping molecules or ions across membranes by active transport
• moving things around inside the cell, such as chromosomes, vesicles or in muscle cells the protein fibres that cause muscle contraction

Question 4

draw a diagram for the use of ATP

Answer 4

ADP + phosphate —-(cell respiration)–> ATP

ATP ——(active cell processes)—-> ADP + Pi

Question 5

When does anaerobic cell respiration take place?

Answer 5

• When a short but rapid burst of ATP production is needed
• When oxygen supplies run out in respiring cells
• In environments that are deficient in oxygen (eg waterlogged soils)

Question 6

give the equation for anaerobic respiration in :
1. animals
2. yeasts and plants

Answer 6

glucose —(ADP->ATP)—-> Lactate

glucose —(ADP->ATP)—–> ethanol + carbon dioxide

Question 7

Describe yeast and its uses in making bread

Answer 7

Bread is made by adding water and yeast to flour, then kneading it:
1. The dough is kept warm to encourage the yeast to respire
2. Oxygen in the dough is soon used up so the yeast carries out anaerobic cell respiration.
3. The CO2 produced cannot escape and forms bubbles
4. Rising= the swelling of the dough due to these bubbles
5. Ethanol is also produced but evaporates during baking

Question 8

describe yeast and its uses in making bioethanol

Answer 8

• bioethanol is produced from sugar cane and corn (maize) using yeast
• yeast converts sugars into ethanol in large fermenters by anaerobic respiration.
• starch and cellulose must first be broken down into sugars using enzymes
• the ethanol produced is purified by distillation and various methods are then used to remove water from it to improve its combustion

Question 9

when is anaerobic respiration used in humans?

Answer 9

to maximise the power of muscle contractions:
- Muscle contractions require the expenditure of high amounts of energy and thus require high levels of ATP
- When exercising at high intensity, the cells’ energy demands will exceed what the available levels of O2 can supply aerobically
- Hence the body will begin breaking down glucose anaerobically to maximise ATP production
- This will result in an increase in the production of lactic acid, which leads to muscle fatigue
- When the individual stops exercising, oxygen levels will increase and lactate will be converted back to pyruvate

Question 10

describe the difference between anaerobic and aerobic cell respiration

Answer 10

anaerobic cell respiration gives a small yield of ATP from glucose
aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose

Question 11

ATP from cell respiration is ——- available as a source of energy in the cell

Answer 11

immediately

Question 12

describe the two key points relating to respirometers

Answer 12

1. an alkali is used to absorb CO2, so reductions in volume are due to oxygen use.
2. Temperature should be kept constant to avoid volume changes due to temperature fluctuations.

Question 13

state the 4 main stages of respiration

Answer 13

Glycolysis- 2ATP
Link reaction
Krebs cycle- 2ATP
Oxidative phosphorylation: ETC, chemiosmosis

Question 14

describe glycolysis

Answer 14

In glycolysis, glucose is converted to pyruvate in the cytoplasm.
This gives a small net gain of ATP without the use of oxygen.
check photo

Question 15

describe the link reaction

Answer 15

In aerobic cell respiration pyruvate is decarboxylated (CO2 is removed) and oxidised (loses electrons) to form an acetyl compound. It is then attached to coenzyme A to form acetyl coenzyme A.

This is because pyruvate alone can’t enter the Krebs cycle

check diagram

Question 16

describe Krebs cycle

Answer 16

The second stage of aerobic respiration is the Krebs cycle, which occurs within the matrix of the mitochondria
Here, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide.

Acetyl CoA transfers its acetyl group to a 4C compound (oxaloacetate) to make a 6C compound (citrate)
Coenzyme A is released and can return to the link reaction to form another molecule of acetyl CoA

check diagram

Question 17

describe oxidative phosphorylation: ETC, chemiosmosis

Answer 17

During glycolysis, link reaction, and Krebs, FAD and NAD molecules get reduced- they accept electrons and hydrogen ions which they are now carrying to cristae of the mitochondria.
1. NADH + H+ supplies pairs of hydrogen atoms to the first carrier in the chain, with the NAD+ returning to the matrix.
2. The hydrogen atoms are split, to release two electrons, which pass from carrier to carrier in the chain.
3. Energy is released as the electrons pass from carrier to carrier, and three of these use this energy to transfer protons (H+) across the inner mitochondrial membrane, from the matrix to the intermembrane space. As electrons continue to flow along the chain and more and more protons are pumped across the inner mitochondrial membrane, a concentration gradient of protons builds up. 4. This proton gradient is a store of potential energy/electrochemical gradient (proton motive force)
5. To allow electrons to continue to flow, they must be transferred to a terminal electron acceptor at the end of the chain. In aerobic respiration this is oxygen, which briefly becomes 2O2-, but then combines with two H+ ions from the matrix to become water.
6. Protons pass back from the intermembrane space to the matrix through ATP synthase. As they are moving down the concentration gradient, energy is released and this is used by ATP synthase to phosphorylate ADP.

Question 18

describe the role of oxygen in aerobic respiration

Answer 18

Oxygen is needed to bind with the free protons to form water to maintain the hydrogen gradient. Without oxygen, hydrogen ions would simply build up, and the chain would come to a halt.

Question 19

describe how the structure of the mitochondria is adapted to the function it performs.

Answer 19

check diagram

Question 20

Decarboxylations:

Answer 20

Carbon dioxide lost
Enzymes- decarboxylases

Question 21

Lysis:

Answer 21

Larger molecules split into smaller ones

Question 22

Phosphorylations:

Answer 22

Phosphate groups added to a substrate
Enzymes- phosphorylases
Source of the phosphate is often ATP
Phosphorylation of molecules makes them less stable.

Question 23

Oxidations:

Answer 23

Oxygen added to a substrate
Hydrogen removed from a substrate
Electrons lost
Enzymes- oxidases

Question 24

Reductions:

Answer 24

Hydrogen added to a substrate
Oxygen removed
Electrons gained
Enzymes- reductases

Question 25

NAD types

Answer 25

Oxidised: NAD+
Reduced: NADH
NAD+ + H+ + 2e- ⇔ NADH

Question 26

FAD types

Answer 26

Oxidised: FAD
Reduced: FADH2
FAD + 2H+ + 2e- ⇔ FADH2