IGCSE Biology Paper-1: Specimen Questions with Answers 120 - 121 of 208

Question 120

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Question

MCQ▾

The diagram shows the average head and ear shapes of rabbits from four different regions.

Which is best adapted to living in the coldest region?

Allens Rule Refers to an Ecogeographical Rule

Allen’s Rule Refers to an Ecogeographical Rule

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Choices

Choice (4)
a.B
b.A
c.C
d.D

Answer

a.

Explanation

  • Allen’s rule refers to an ecogeographical rule which states that significant differences exist in the size of limbs and other external organs of animals, even within the same species, depending on the geographical region in which they live. Animals living in colder regions of the world, for instance, have shorter limbs than those living in warmer regions as an adaptation to control the dissipation of heat. A smaller body surface area helps animals in colder regions stay warm by slowing down the loss of body heat. It is named after American biologist Joel Asaph Allen who proposed it in his 1877 paper “The influence of physical conditions in the genesis of species. “
Jackrabbit and Arctic Hare

Jackrabbit and Arctic Hare

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Question 121

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MCQ▾

A plant cell undergoes plasmolysis when it is placed in ________ solution?

A plant cell undergoes plasmolysis

A Plant Cell Undergoes Plasmolysis

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Choices

Choice (4)
a.Isotonic
b.Hypertonic
c.Hypotonic
d.Pure water

Answer

b.

Explanation

  • Plasmolysis (Gr. Plasma = something formed; lysis = loosing): If a living plant cell is placed in a highly concentrated solution (i. e. hypertonic solution), water comes out of the cell due to exosmosis, through the plasma membrane. The loss of water from the cell sap causes shrinkage of the protoplast away from the cell wall in the form of a round mass in the center. “The shrinkage of the protoplast of a living cell from its cell wall due to exosmosis under the influence of a hypertonic solution is called plasmolysis. ” The stage of plasmolysis, when the protoplast just begins to contract away from the cell wall is called incipient plasmolysis. The stage when the cell wall has reached its limit of contraction and the protoplast has detached from cell wall attaining spherical shape is called evident plasmolysis. In a plasmolysis cell, the space between the contracted protoplast and the cell wall remains filled with external solution. If a cell with incipient plasmolysis is placed in a hypertonic solution it will show more plasmolysis.