2.8 Cell Respiration

Question 1

What does respiration do? SL

Answer 1

Releases energy from organic compounds to produce ATP.
The source of organic compounds can be glucose, starch, lipids or even amino acids from proteins if we eat more than needed.

Question 2

How is ATP formed? SL

Answer 2

ATP is formed from the phosphorylation of ADP, energy is required.

Question 3

What is the advantage of ATP?

Answer 3

The energy is immediately available. It is simply released by removing a phosphate group.

Question 4

Why do cells require a constant source of ATP?

Answer 4

When ATP is used for the cells activities for example synthesising molecules, movement, pumping molecules, it is eventually released as heat. Heat cannot be converted back into chemical energy and therefore it is eventually lost to the environment.

Question 5

What is Anaerobic respiration?

Answer 5

Anaerobic cell respiration gives a small yield of ATP from glucose. Glucose is broken down without using any oxygen. It is used in 3 situations:

• When a short but rapid burst of ATP production is needed
• When oxygen supplies run out
• In environments that are deficient in oxygen, for example waterlogged soils.

HUMANS:
Glucose (ADP) = lactate + (ATP)

YEAST AND PLANTS
Glucose = ethanol and carbon dioxide

Question 6

What is the anaerobic respiration equation in humans?

Answer 6

Glucose (ADP) = lactate + (ATP)

Question 7

What is the anaerobic respiration equation in animals?

Answer 7

Glucose = ethanol and carbon dioxide

Question 8

What are the uses of yeast?

Answer 8

Yeast is a unicellular fungus that occurs naturally in habitats where glucose or other sugars are available, such as the surface of fruits. It can respire aerobically or anaerobically.

• In bread - Yeast (is often added) in bread when it respires anaerobically produces carbon dioxide which then cannot escape from the dough and forms bubbles. This swells the dough and makes it rise. Ethanol is also produced but it evaporates during baking.
• Production of bioethanol - most bioethanol is produced from sugar cane and corn using yeast. Yeast converts the sugars into ethanol in large fermenters but anaerobic respiration. Only sugars can be converted, so starch and cellulose must first be broken down into sugars. This is done using enzymes. Then the ethanol is distilled to remove the water and it is used for fuel in vehicles.

Question 9

What is yeast?

Answer 9

Yeast is a unicellular fungus that occurs naturally in habitats where glucose or other sugars are available, such as the surface of fruits. It can respire aerobically or anaerobically.

Question 10

When is anaerobic respiration used?

Answer 10

• When a short but rapid burst of ATP production is needed
• When oxygen supplies run out
• In environments that are deficient in oxygen, for example waterlogged soils.

Sometimes we resort to anaerobic respiration in muscles to maximise the power of muscle contractions.

Question 11

What is oxygen debt?

Answer 11

Anaerobic respiration involves the production of lactate, so when it is being used to supply ATP, the concentration of lactate in the muscles increases. There is a limit to how much the body can tolerate. This is the reason for the short timescale over which the power of muscle contractions can be maximised. We can only sprint for a short distance - not more than 400 metres.

After vigorous muscle contractions the lactate must be broken down. This involves the use of oxygen. It can take several minutes for enough oxygen to be absorbed for all the lactate to be broken down. The demand for oxygen that builds up during a period of anaerobic respiration is called the oxygen debt.

Question 12

What is a respirometer?

Answer 12

Any device that is used to measure respiration rate. There are many possible designs.

• A sealed glass or plastic container in which the organism or tissue is placed.
• An alkali such as potassium hydroxide to absorb carbon dioxide
• A capillary tube containing fluid connected to the container.

If the respirometer is working correctly and the organisms inside are carrying out aerobic cell respiration, the volume of air inside the respirometer will reduce and the fluid inside the capillary tube will move towards the container with the organisms. This is because oxygen is used up and the carbon dioxide produced is absorbed by the alkali.

THERE ARE ETHICAL ISSUES WITH PUTTING ANIMALS INSIDE RESPIROMETERS.