IGCSE Biology Paper-2: Specimen Questions with Answers 196 - 197 of 203

Question 196

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Question

MCQ▾

Which graph shows the effect of pollution by untreated sewage on the amount of oxygen dissolved in a river?

Choices

Choice (4)
a.
Oxygen dissolved in a river
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b.
Oxygen dissolved in a river
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c.
Oxygen dissolved in a river
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d.
Oxygen dissolved in a river
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Answer

a.

Explanation

  • The Domestic Sewage primarily contains Biodegradable organic matter, which is decomposed by bacteria and other microorganisms. The amount of such organic matter in sewage water is measured by BOD (Biochemical Oxygen Demand) method.
  • These organisms rob the dissolved oxygen of water due to which the dissolved oxygen content is sharply declined in down- stream. This depletion of oxygen is responsible for the mortality of planktons, mollusks, fishes and other sensitive organisms (aquatic fauna).
  • Later maximum organisms either microbes or other one starts to die and water again become clearer. This cleared water has large amount of dissolved oxygen and very less amount of BOD.
Oxygen dissolved in a river

Oxygen Dissolved in a River

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Question 197

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MCQ▾

The diagrams show pollen grains from three different species of plant as they appear under the microscope. The diagrams are all to the same scale.

Three different species of plant

Three Different Species of Plant

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Which pollen grains are involved in wind-pollination?

Choices

Choice (4)
a.1 only
b.1 and 2
c.2 only 3
d.2 only

Answer

b.

Explanation

Anemophily (Pollination by wind)

  • When the pollen grains are transferred from one flower to another flower through the air or wind. The flowers involved are known as anemophilous flowers.
  • It is non-directional and is considered a wasteful process since anemophillous plants produce enormous amount of pollen grains. The pollen grains are very small, lightweight and dry and their stigma is hairy or brushy and mucilaginous (sticky).
  • These flowers are neither attractive nor possess fragrance. They do not have nectar glands and are generally unisexual. Eg: Sugar cane, Bamboo, Coconut, Grasses, Maize.
Anemophily (Pollination by wind)

Anemophily (Pollination by Wind)

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