IGCSE Biology Paper-4: Specimen Questions with Answers 67 - 69 of 279
Question 67
Explanation
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.
Passage
There is a flow chart is given in which different type of animals are shown
Question 68 (1 of 2 Based on Passage)
Explanation
Animal A- Giraffe
Animal B- Snake
Animal C-Guppy
Animal D-Tiger
Question 69 (2 of 2 Based on Passage)
Explanation
Animal A is herbivore and animal D is not herbivore.