IGCSE Biology Paper-4: Specimen Questions with Answers 149 - 150 of 279

Passage

An image of a germinating seed showing the growing root

Cell Membrane

Question 149 (1 of 4 Based on Passage)

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There are situations, either in wild plants or in laboratory experiments, where roots do not grow downwards.

Suggest and explain one situation.

Explanation

Clinostat/Klinostat is an instrument which can eliminate the effect of gravity and allow a plant to grow horizontally by slowly rotating it.

The main axis of which is attached to a rod. On the top of the rod is attached a flower pot. The clinostat is kept in a horizontal position as shown in fig. When the clock axis rotates the flower pot also rotates. As a result of this the plant grows horizontally as the effect of gravity is nullified by clinostat. If the clock of the clinostat is stopped the rotation of the plant stops, the shoot apex moves upward (negative geotropism) and the root apex moves downwards (positive geotropism) .

Structure of Plant

Question 150 (2 of 4 Based on Passage)

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Describe and explain how the structures seen at J are adapted for their function.

Explanation

Root Hairs

They are enlargements of special epiblema cells called trichoblasts and occurs in a particular zone of young root called root hair zone. A root hair cell has vacuolated protoplast with nucleus present towards the apical part of hair. They are specialized to absorb water from soil crevices. They also hold soil particles.

Function of Root Hairs

The function of root hairs is to collect water and mineral nutrients that are present in the soil and take this solution up through the roots to the rest of the plant. As root hair cells do not carry out photosynthesis, they do not contain chloroplasts.

Cell Membrane and Cell Wall