(a) Describe the process of inhalation in man . (b) Describe briefly the process of gaseous exchange in the shoo: system of flowering plants. (c) Describe a...

(a) Process of inhalation (breathing in) in man

1. The external intercostal muscles contract, pulling the ribs upwards and outwards.
2. The diaphragm muscles contract, so the diaphragm flattens and moves downwards.
3. These two movements increase the volume of the thoracic cavity (chest).
4. The increased volume lowers the air pressure inside the lungs below atmospheric pressure.
5. Because outside air is now at higher pressure, air rushes in through the nose and trachea into the lungs, and the lungs inflate.

(b) Gaseous exchange in the shoot system of flowering plants

In the shoot, gaseous exchange takes place mainly through the stomata of the leaves (and through lenticels in woody stems). Gases diffuse in and out through these openings and through the air spaces of the spongy mesophyll. By day, when photosynthesis is faster than respiration, carbon dioxide diffuses in and oxygen diffuses out. At night, when only respiration occurs, oxygen diffuses in and carbon dioxide diffuses out. The exchange is by simple diffusion along concentration gradients across the moist cell surfaces.

(c) Experiment to demonstrate the effect of distilled water on mammalian red blood cells

1. Obtain a fresh sample of blood and place a drop in a test tube.
2. Add a quantity of distilled water to the blood and mix gently.
3. Place a drop on a slide and examine under a microscope; also observe the colour of the mixture.
4. Observation: the red cells swell, become spherical and burst; the mixture turns clear red because the haemoglobin is released.
5. Explanation / conclusion: distilled water is hypotonic to the cell contents, so water enters the cells by osmosis until they burst. This bursting is called haemolysis.