(a)(i) Briefly explain the term respiration. (ii) Name the two types of respiration and write a balanced equation to summarize each of them. (b) Outline the...

Answer Details

(a)(i) Respiration

Respiration is the biochemical process by which food substances (chiefly glucose) are broken down within living cells to release energy, which is stored as ATP for the various activities of the organism. It usually involves the intake of oxygen and the release of carbon dioxide and water.

(a)(ii) Two types of respiration with balanced equations

Aerobic respiration (in the presence of oxygen):

\[ C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy} \]

Anaerobic respiration (in the absence of oxygen):

In plants/yeast (alcoholic fermentation):

\[ C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{energy} \]

In animal muscle (lactic acid formation):

\[ C_6H_{12}O_6 \rightarrow 2C_3H_6O_3 + \text{energy} \]

(b) Mechanisms of breathing in human beings

(i) Inhalation (breathing in)

• The muscles of the diaphragm contract so that the diaphragm flattens and moves downward.
• The external intercostal muscles contract, pulling the ribs upward and outward.
• These increase the volume of the thoracic cavity and lower the pressure inside the lungs below atmospheric pressure.
• Air therefore rushes in through the nose and trachea into the lungs, which inflate.

(ii) Exhalation (breathing out)

• The muscles of the diaphragm relax so that the diaphragm curves upward (dome-shaped) again.
• The external intercostal muscles relax, allowing the ribs to move downward and inward.
• These decrease the volume of the thoracic cavity and raise the pressure inside the lungs above atmospheric pressure.
• Air is therefore forced out of the lungs through the trachea and nose.