Theory question 102
Respiration(a) Describe the process of inhalation in man
(b) Describe briefly the process of gaseous exchange in the shoot system of flowering plants
(c) Describe an experiment to demonstrate the effect of distilled water on mammalian red blood cell.
Show the model answer
(a) External intercostal muscles contract, ribs move upwards and outwards; diaphragm muscles contract and the diaphragm flattens (moves down); volume of thoracic cavity increases, pressure inside falls below atmospheric pressure; air rushes in through nose, trachea and bronchi into the lungs
(b) Gases diffuse through stomata in leaves (and lenticels in woody stems) into intercellular air spaces; they dissolve in the moist cell walls and diffuse into/out of cells; in daylight CO₂ enters and O₂ leaves (photosynthesis greater than respiration); at night O₂ enters and CO₂ leaves
(c) Put a drop of blood in distilled water and a drop in 0.9% salt (isotonic) solution as control; observe under a microscope after a few minutes
In distilled water the red cells swell and burst (haemolysis) because water enters by osmosis – the liquid turns clear red; in salt solution the cells stay normal
In (c) explain the result in terms of osmosis.