IGCSE Biology Paper-4: Specimen Questions with Answers 227 - 230 of 279

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Passage

Humans need vitamin D as part of their diet.

Question 227 (2 of 2 Based on Passage)

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Short Answer▾

Describe the effects of vitamin D deficiency in humans.

Explanation

Increased risk of death from cardiovascular disease

  • Cognitive impairment in older adults
  • Severe asthma in children
  • Cancer

Passage

Shows part of the nitrogen cycle.

Protein Synthesis

Question 228 (1 of 6 Based on Passage)

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Define the term deamination.

Explanation

Removal of the amine group from amino acids - part of ammonification.

Question 229 (2 of 6 Based on Passage)

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State the name of an enzyme that digests proteins.

Explanation

Proteases, pepsin, trypsin are enzymes which digests protein.

Pepsin a protein-digesting enzyme secreted in gastric juice. Trypsin a protein-digesting enzyme in pancreatic juice that is released into the small intestine.

Question 230 (3 of 6 Based on Passage)

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Short Answer▾

State the names of processes P and Q in Fig.

process P

process Q

Explanation

P – Denitrification

Denitrification

The conversion of nitrates and nitrites in soil into atmospheric is called denitrification, which is done by denitrifying bacteria, e. g. , Micrococcus denitrificans and Bacillus denitrificans, Pseudomonas & Thiobacillus.

Denitrification occurs in four steps:

  • Nitrates are reduced to nitrites by the enzyme nitrate reductase. The nitrites are reduced to ammonia by nitrite reductase. The ammonia is so formed is enzymatically incorporated in amino acids.
  • Denitrification does not occur to any significant degree in well aerated soils with moderate number of nitrates and organic matter. It occurs in water logged anaerobic soils with high organic matter content.

Q - Nitrification

Nitrification

The conversion of in soil into nitrates and nitrites is called nitrification. It is done by nitrifying bacteria, e. g. , Nitrosomonas, Nitrosococcus (convert into nitrites) and Nitrobacter (convert nitrites into nitrates) .

  • Nitrifying bacteria are chemoautotrophs and are benefitted by utilizing energy released in oxidation, which is used in chemosynthesis. At soil temperature in alkaline soils and with sufficient moisture and aeration the activity of ammonifying and nitrifying bacteria is found to be maximum.
  • The nitrate thus formed is absorbed by plants and is transported to the leaves. In leaves, it is reduced to form ammonia that finally forms the amine group of amino acids.

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