IGCSE Biology Paper-1: Specimen Questions with Answers 193 - 194 of 208

Question 193

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Question

MCQ▾

Following is/are the current sequence of eutrophication resulting in drying of the ponds.

1 fish die

2 algae grow

3 oxygen decreases

4 bacteria grow

What is the correct sequence of these events?

Choices

Choice (4)
a.
b.
c.
d.

Answer

a.

Explanation

Changes in pond water when organic waste is mixed in water. The microbes present in water start the degradation which reduces the D. O (dissolved oxygen) rapidly. This decrease affects the aquatic fish and other animals and plants. There are several organic matters in water which causes increase in water algae or algal bloom, imparting distinct colour to the water. This algal growth causes water quality deterioration. The bloom has algae which affects the animals and plants. There are bright colored flowers growing or floating on water bodies which look beautiful. However, these flowers grow or spread along the water surface which interrupts the water ways. Their growth speed is fast and thus difficult to remove them.

Food, Habitat and Oxygen Production

Food, Habitat and Oxygen Production

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Question 194

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Question

MCQ▾

The graph shows the numbers of May fly in a clean pond.

Condition P on the Graph

Condition P on the Graph

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What might have been responsible for the condition P on the graph?

Choices

Choice (4)
a.increase in the food of May flies
b.addition of predators which feed on May flies
c.increase in solar light around pond
d.addition of plants in the pond

Answer

b.

Explanation

Predation

  • It is the act in which a predator organism feeds on a victim called prey. It may or may not result in the death of the prey. (Mostly it does).
  • It is a mechanism by which energy fixed by plants moves to the higher trophic levels.
  • Example- tigers feed on deer.
  • Predators play important roles in ecosystem.
  • They help to keep the prey population under check.
  • They help to maintain species diversity in a community by reducing the intensity of competition among competing prey species.
  • Examples
  • Grazers of a grassland may prevent a single dominant species from taking over.
  • The elimination of wolves from Yellowstone National Park led to herbivores over-grazing many woody browse species, affecting the area’s plant populations.
  • In addition, wolves often kept animals from grazing in riparian areas, which protected the food of beavers. The removal of wolves had a direct effect on beaver populations, as their habitat became territory for grazing.