B6. Respiration

Question 1

Define ‘respiration’.

Answer 1

The chemical reactions that break down nutrient molecules in living cells to release energy.

Question 2

Name the uses of energy in the body of humans.

Answer 2

• Muscle contraction
• Protein synthesis
• Cell division
• Growth
• The passage of nerve impulses
• Maintenance of a constant body temperature

Question 3

State the word equation for aerobic respiration.

Answer 3

Glucose + oxygen -> carbon dioxide + water

Question 4

State the symbol equation for aerobic equation.

Answer 4

C6H12O6 + 6O2 -> 6CO2 + 6H2O

Question 5

Define ‘aerobic respiration’.

Answer 5

The release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen.

Question 6

Define ‘anaerobic respiration’.

Answer 6

The release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen.

Question 7

State the word equation for anaerobic respiration in muscles during hard exercise and in yeast.

Answer 7

In muscles: Glucose -> lactic acid

In microorganism yeast: Glucose -> alcohol + carbon dioxide

Question 8

Describe the effect of lactic acid in muscles during exercise.

Answer 8

• When exercising vigorously, the blood cannot supply enough oxygen to the muscles for aerobic respiration.
• Therefore the muscles respire anaerobically;
• Lactic acid builds up in the muscles and causes cramp;
• The liver breaks down lactic acid with oxygen;
• When you stop exercising, you go on breathing hard to get oxygen to break down the lactic acid;
• This is called an oxygen debt because during vigorous exercise you ‘borrowed’ some extra energy, without ‘paying’ for it with oxygen;
• When all the lactic acid has been broken down, your breathing rate and rate of heart beat return to normal.

Question 9

Describe the role of anaerobic respiration in yeast during brewing.

Answer 9

• To make beer, yeast is dissolved in a warm liquid containing the sugar maltose
• The yeast respires anaerobically by a process called fermentation
• This process produces ethyl alcohol (ethanol) making the drink alcoholic
• And carbon dioxide which makes the drink fizzy

Question 10

Describe the role of anaerobic respiration in yeast during bread-making.

Answer 10

• Yeast is mixed with water and sugar to activate it.
• The mixture is added to flour to make dough, and left in warm place
• The dough rises as the yeast respires and releases carbon dioxide, which gets trapped in the dough;
• When the dough is cooked, the high temperature kills the yeast and evaporates any alcohol formed;
• Air spaces are left where the carbon dioxide was trapped, which gives the bread a light texture

Question 11

Compare aerobic and anaerobic respiration in terms of relative amounts of energy release.

Answer 11

Aerobic respiration:

• Uses oxygen
• No alcohol or lactic acid made
• Large amount of energy released from each molecule of glucose
• Carbon dioxide made

Anaerobic respiration:

• Does not use oxygen
• Alcohol or lactic acid is made
• Much less energy released from each molecule of glucose
• Carbon dioxide is made by yeast and plants, but not by animals

Question 12

List the features of gas exchange surfaces in animals.

Answer 12

• Walls of the alveolus is thin (a single layer of cells) to allow gases to diffuse across them quickly;
• They are moist to prevent the cells from drying and to allow gases to dissolve;
• They have a large surface area, so that a lot of gas can diffuse across at the same time;
• They have a high concentration gradient - maintained by the movement of air and food

Question 13

Explain the role of mucus and cilia protecting the gas exchange system from the pathogens and particles

Answer 13

• The lining contains two kinds of cells: Goblet cells and ciliated cells;
• Goblet cells make sticky, slimy mucus
• Many of the bacteria in the air and dust particles get trapped in the mucus.
• Ciliated cells have tiny, microscopic hair on them called cilia;
• The cilia beat in unison, and sweep the mucus upwards, towards the back of the throat.

Question 14

Describe the effects of carbon monoxide on the gas exchange system.

Answer 14

A poisonous gas; combines with haemoglobin in RBC, preventing them from transporting oxygen

Question 15

Describe the effects of nicotine on the gas exchange system.

Answer 15

Addictive; increases heart rate and blood pressure

Question 16

Describe the effects of smoke particles on the gas exchange system.

Answer 16

Irritate the air passages, causing inflammation and increased mucus production, resulting in chronic bronchitis; coughing and the presence of particles in the alveoli can lead to emphysema (breaking the walls of the alveoli)

Question 17

Describe the effects of tar on the gas exchange system.

Answer 17

A carcinogen - increases the risk of lung cancer; lines the air passages, increasing mucus production and paralysing and damaging cilia, causing bronchitis.

Question 18

Explain the effects of physical activity on the rate and depth of breathing.

Answer 18

 The volume of air breathed in and out during normal, relaxed breathing is about 0.5 litres (the tidal volume);
 The breathing rate is about 12 breaths per minute;
 During exercise, the volume inhaled (depth) increases to about 5 litres ( depending on the age, sex, size and fitness of the person);
 The maximum amount of air breathed in and out in one breath is the vital capacity;
 The breathing rate can increase to over 20 breaths per minute;
 The total lung volume is greater than the vital capacity because some air always remains in the lungs (otherwise the lungs would collapse and the alveoli walls would stick together)
 Breathing rate and depth increase to absorb more oxygen for the muscles as exercising muscles need to respire more to get more energy.