Biology
A candidate in order to study the process of osmosis has taken 3 potato cubes and put them in 3 different beakers containing 3 different solutions. After 24 hours, in the first beaker the potato cube increased in size, in the second beaker the potato cube decreased in size and in the third beaker there was no change in the size of the potato cube. The following diagram shows the result of the same experiment:
(i) Give the technical terms of the solutions used in beakers 1, 2 and 3.
(ii) In beaker 3, the size of the potato cube remains the same. Explain the reason in brief.
(iii) Write the specific feature of the cell sap of root hairs which helps in absorption of water.
(iv) What is osmosis?
(v) How does a cell wall and a cell membrane differ in their permeability?
Roots Absorption
ICSE 2014
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Answer
(i) The technical terms of the solutions used in beakers 1, 2 and 3 are:
Beaker 1 — Hypotonic solution.
Beaker 2 — Hypertonic solution.
Beaker 3 — Isotonic solution.
(ii) In beaker 3, the solution present is an isotonic solution, i.e. the relative concentration of water molecules and solutes is the same in the solution as well as inside the cell. There is no movement of water molecules across the cell membrane. Hence, the size of potato cubes remains the same.
(iii) The cell sap of root hair has a higher concentration of solute than the surrounding water. Due to this endosmosis takes place helping the root hairs in absorption of water.
(iv) Osmosis is the movement of water molecules from their region of higher concentration (dilute solution or with a lower solute concentration) to their region of lower concentration (concentrated solution or with a higher solute concentration) through a semi-permeable membrane.
(v) The cell wall is freely permeable to all substances, while the cell membrane is selectively permeable and allows only certain substances to enter or exit the cell.
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