IGCSE Biology Paper-1: Specimen Questions with Answers 143 - 144 of 208

Question 143

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Question

MCQ▾

The diagram shows a plant.

Water Absorbed by this Plant

Water Absorbed by this Plant

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What is the pathway taken by most of the water absorbed by this plant?

Choices

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

Answer

c.

Explanation

  • The main force that draws water from the soil and through the plant is caused by a process called transpiration. Water evaporates from the leaves and causes a kind of ‘suction, ’ which pulls water up the stem. The water travels up the xylem vessels in the vascular bundles and this flow of water is called the transpiration stream. The water cycle is different from other cycles because only a tiny proportion of the water that is recycled passes through living organisms. Animals lose water by evaporation, defecation, urination, and exhalation. They gain water from their food and drink. Plants take up water from the soil and lose it by transpiration. Millions of tonnes of water are transpired, but only a tiny fraction of this has taken part in the reactions of respiration or photosynthesis.
Water in the Soil

Water in the Soil

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Question 144

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Question

MCQ▾

Phloem is an example of

Choices

Choice (4)
a.a cell
b.an organ
c.an organ system
d.a tissue

Answer

d.

Explanation

Phloem (bast): Term “Phloem” was given by Nageli. Its main function is the transport of organic food materials from leaves to stem and roots in a downward direction.

It consists of the following elements:

  • Sieve element
  • Companion cells
  • Phloem parenchyma
  • Phloem fiber or bast fiber

Sieve Element

  • They are long tube-like cells placed end to end, forming a continuous channel in the plant parts.
  • Their cell wall is made up of cellulose.
  • Their transverse wall is perforated like a normal sieve and hence they are called as sieve tubes.
  • Nucleus is not found in these cells.
  • Each sieve tube has a lining of cytoplasm near its periphery.
  • Callus pad may be visible in the winter season.
  • Their main function is to translocate the food material from one part to the other.

Companion Cells

  • They are thin-walled cells which are associated with sieve tubes.
  • They are elongated.
  • They relate to the sieve tube through sieve pore.
  • They contain nucleus and are therefore, living in nature.
  • They are not found in pteridophytes and gymnosperms but are always present in angiosperms.

Phloem Parenchyma

  • The parenchyma associated with the phloem is called phloem parenchyma.
  • The cells are elongated with rounded ends and possess cellulosic cell walls.
  • These cells are living and store food reserves in the form of starch and fats.
  • They are present in pteridophytes and most of dicotyledonous angiosperms.
  • They are absent in monocots.

Phloem or Bast Fiber

  • The sclerenchyma fiber associated with the phloem are called as phloem fiber.
  • These are also known as bast fiber. The fiber is elongated lignified cells with simple pits. The ends of these cells may be pointed, needle like or blunt. They are non-living cells that provide mechanical support to the organs.
Longitudinal View and Transverse Section

Longitudinal View and Transverse Section

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