IGCSE Biology Paper-4: Specimen Questions with Answers 67 - 69 of 279

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Question 67


Describe in Detail


What is the microbial ecology of the nitrogen cycle?


The nitrogen cycle is the conversion of nitrogen into its different forms by the use of microorganisms. In nitrogen fixation, atmospheric nitrogen is fixed to be used by plants. It is done by many symbiotic bacteria (diazotrophs) . These bacteria have nitrogenase enzyme that combines with N2 gas with hydrogen to produce ammonia. Rhizobium and azotobactors are the example of it.

Here they form a mutualistic relationship with the plant, producing ammonia in exchange for carbohydrates. Sometimes bacteria or fungi convert the organic nitrogen within the remains back into ammonium (NH4 + ) , a process called ammonification and the process of conversion of ammonia to nitrate is also done by soil-living bacteria such as nitrobacterium. Nitrification process is performed by bacterial species such as pseudomonas and clostridium.


There is a flow chart is given in which different type of animals are shown

Shows Given Charts in Different Types of Animals

Question 68 (1 of 2 Based on Passage)


Write in Brief

One Liner▾

What is the difference between animal A and Animal D?


Animal A is herbivore and animal D is not herbivore.

Question 69 (2 of 2 Based on Passage)


Write in Short

Short Answer▾

Identify them from (Guppy, Snake, Giraffe and tiger)


Animal A- Giraffe

Animal B- Snake

Animal C-Guppy

Animal D-Tiger

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