IGCSE Biology Paper-1: Specimen Questions with Answers 186 - 186 of 208

Question 186

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Question

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The diagram shows part of the water cycle.

Water Cycle

Water Cycle

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The process responsible for loss of water from the tree?

Choices

Choice (4)
a.Osmosis
b.Condensation
c.Evaporation
d.Transpiration

Answer

d.

Explanation

  • Though large quantities of water are absorbed by the roots from soil, but only 2 - 5 % of it is utilized by plant and rest 95 - 98 % is lost in form of transpiration.
  • The loss of water from the aerial parts of plant in the form of vapours is called transpiration.
  • The instrument used for measuring transpiration is potometer.
  • The minimum transpiration is found in succulent xerophytes and no transpiration in submerged hydrophytes.
  • Maximum transpiration is found in Mesophytes.

Significance of Transpiration

In Regulation of Temperature

  • Cooling effect on the surface of leaves is produced by the process of transpiration, due to which temperature remains constant in plants.
  • The plant is protected from the burning of heat due to transpiration. Evaporation of water produces cooling effect.

In Mineral Absorption

  • Mass flow of water is found during the passive absorption of water. Hence it is assumed that minerals enter the roots through the water.
  • In ascent of sap
  • In water absorption
  • Distribution of absorbed salts
  • Gaseous exchange
  • Control of hydrological cycle