Theory question 106
Cell and Its Environment(a) Explain the term osmosis
(b) Describe an experiment to show that the xylem tissue conducts water from the root to the shoot
(c) (i) Explain what happens to a red blood cell when placed in a hypotonic solution (ii) Mention three conditions that may cause haemolysis.
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(a) Osmosis is the movement of water molecules from a dilute solution (high water concentration) to a more concentrated solution (low water concentration) through a semi-permeable membrane.
(b) Place a leafy shoot (e.g. Balsam) or uprooted seedling with its roots in water coloured with eosin (red dye) for a few hours. Cut transverse sections of the stem/root and look at them under a microscope (or hand lens). Only the xylem vessels are stained red, showing that water moves up through the xylem. (A control in plain water shows no stain.)
(c)(i) Water enters the red blood cell by osmosis because the solution outside is more dilute than its cytoplasm; the cell swells and, having no cell wall, bursts (haemolysis), releasing haemoglobin.
(ii) Any three: placing red cells in a hypotonic solution or distilled water; some snake venoms; malaria parasites; incompatible blood transfusion; some bacterial toxins/chemicals; sickle-cell crisis.
Red cells have no wall, so in a weak solution they burst.