IGCSE Biology Paper-4: Specimen Questions with Answers 127 - 128 of 279

Passage

Plants produce glucose in leaves and convert some of it to sucrose.

Question 127 (2 of 7 Based on Passage)

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The movement of sucrose in plants can be modelled using laboratory apparatus.

Fig. shows the apparatus used to model the movement of sucrose in a plant:

  • Partially permeable bags were attached tightly to the ends of tube X.
  • The bag representing a source was filled with a colored sucrose solution.
  • The bag representing a sink was filled with water.
  • The containers and tube X and tube Z were filled with water.
Movement of Sucrose Solution

Fig. shows the position of the colored sucrose solution 45 minutes after the apparatus was set up.

The arrows show the direction of the movement of the liquids.

Sucrose Solution

(i) State the name of the tissue represented by tube X and the name of the tissue represented by tube Z in Fig.

X …

Z …

Explanation

X – the movement of sugars in the phloem begins at the source, where sugars are loaded (actively transported) into a sieve tube. Loading of the phloem sets up a water potential gradient that facilitates the mass movement in the phloem.

Z – Xylem, water in the adjacent xylem moves into the phloem by osmosis.

Question 128 (3 of 7 Based on Passage)

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Amino acids are also transported through plants.

State the name of the mineral ion that is used to make amino acids.

Explanation

Nitrogen

  • Source: The chief source of nitrogen for green plants is the soil. It is absorbed mainly in the form of nitrate ions . The major sources of nitrate for the plants are sodium nitrate, potassium nitrate, ammonium nitrate and calcium nitrate. Under suitable conditions, ammonium ions may substitute for nitrate ions, being easily absorbed by plants. Ordinary green plants cannot utilize elemental nitrogen which constitutes about of the air. It is also trapped by nitrogen fixing bacteria which live symbiotically in root nodules of the plants.
  • Functions: Nitrogen is an essential constituent of proteins, nucleic acids, vitamins, and many other organic molecules as chlorophyll. Nitrogen is also present in various hormones, coenzymes, and ATP etc. It plays an important role in protein synthesis, respiration, growth and in almost all metabolic reactions.

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