This set of Microbiology Multiple Choice Questions & Answers (MCQs) focuses on “Soil Microbiology – Nitrogen Cycle”.
1. Ammonia oxidizers and nitrite oxidizers are ______________
a) Gram-negative chemolithotrophs
b) Gram-positive chemolithotrophs
c) Gram-negative photolithotrophs
d) Gram-positive photolithotrophs
Explanation: Oxidation of ammonia to nitrite by ammonia-oxidizing bacteria and oxidation of nitrite to nitrate by nitrite-oxidizing bacteria are both Gram-negative chemolithotrophs.
2. Alanine gives pyruvic acid on deamination.
Explanation: The process of removal of the amino group from amino acids is known as deamination. Alanine in presence of alanine deaminase gives pyruvic acid and ammonia as its deamination reaction products.
3. How much time does nitrifying bacteria require to grow at an incubation of 250 to 300 C?
a) 1 day
b) 2-3 days
c) 15 days
d) 1 to 4 months
Explanation: For the growth of nitrifying bacteria a relatively large inoculum is used, and incubation is in the dark at 250 to 300 C for a period of 1 to 4 months.
4. Nitrosococcus nitrosus is a nitrite-oxidizing bacteria.
Explanation: Nitrosococcus nitrosus is a type of ammonia-oxidizing bacteria. They usually have an extensive membrane system within their cytoplasm and frequently form cysts and zooglea.
5. Which among the following is not an ammonia-oxidizing bacteria?
a) Nitrosomonas europaea
b) Nitrosovibrio tenuis
c) Nitrospina gracilis
d) Nitrosococcus oceanus
Explanation: Nitrospina gracilis is a nitrite-oxidizing bacteria. They are involved in the oxidation of nitrite to nitrate.
6. Agrobacterium is involved in which of the following processes?
c) Reduction of nitrate to ammonia
Explanation: The transformation of nitrates to gaseous nitrogen is known as denitrification. Species of several bacteria like Agrobacterium, Bacillus, Pseudomonas etc are involved in this process.
7. Which of the following conditions decreases the level of denitrification?
a) Abundance of organic matter
b) Acidic pH
c) Elevated temperatures
d) Availability of oxygen
Explanation: The process of denitrification is enhanced in soils by the presence of abundance of organic matter, by elevated temperatures, by neutral or alkaline pH. The availability of oxygen has a dual effect on denitrification.
8. Which of the following are not the features of component II of nitrogenase enzyme complex?
a) component II is nitrogenase reductase
b) component II is known as the MoFe protein
c) contains sulfur
d) not active without component I
Explanation: Component II of nitrogenase enzyme complex is nitrogenase reductase. It is a smaller molecule and is designated the Fe protein. Both molecules contain sulfur and neither is active without the other.
9. Which of the following is symbiotic nitrogen fixing bacteria?
a) Rhizobium trifolii
b) Clostridium pasteurianum
c) Azotobacter sp.
d) Escherichia coli
Explanation: Symbiotic nitrogen fixation is accomplished by bacteria of the genus Rhizobium in association with legumes like Rhizobium trifolii.
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