Tag: zoology

Questions Related to zoology

Carefully read the following reactions carried out by nitrifying bacteria. Identify the statement about these equations which is not true.
2NH$ _3$+3O$ _2$ $\rightarrow$ 2NO$^- _2$ +2H$^+$ +2H$ _2O$ ---- (I)
2NO$^- _2$+O$ _2$ $\rightarrow$ 2NO$^- _3$ ---- (II)

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Step I is carried out by Nitrosomonas or Nitrosococcus

  2. Step II is carried out by Nitrobacter

  3. Both the steps I and II can be called nitrification

  4. Both the steps occur only in photoautotrophs

Show answer
Correct Option: D
Explanation:
I) In the first step, ammonia is oxidised to nitrites by the action of nitrosomonas and nitrococcus bacteria.
II) In the second step, nitrate is further oxidised to nitrate with the help of nitrobacter and nitrocystis.
Both the reaction is involved in the process of nitrification. These nitrifying bacteria involved are called chemoautotrophs.
So the correct answer is 'Both the steps occur only in photoautotrophs'.

Which one is not a free living nitrogen fixer?

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Rhodospirillum

  2. Azotobacter

  3. Rhizobium

  4. Bacillus

Show answer
Correct Option: C
Explanation:

The organisms involved in nitrogen fixation are termed as nitrogen-fixing organisms. They convert free nitrogen (gaseous form dinitrogen, N2) into forms such as nitrates and nitrites that can be utilized by plants. These organisms could either be free-living or found in symbiotic, mutualistic, or commensalistic relationships with other plants etc. Rhizobium is found in a symbiotic relationship with plant roots. 

So, the correct answer is 'Rhizobium'.

Which of the following is free-living bacteria responsible for nitrogen fixation 

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Pseudomonas

  2. Rhodospirillum

  3. Azotobacter

  4. All of these

Show answer
Correct Option: D
Explanation:

Nitrogen-fixing microorganisms are recognized: free-living (non-symbiotic) bacteria, including the cyanobacteria. Anabaena and Nostoc and genera such as Azotobacter, Beijerinckia, and Clostridium and mutualistic bacteria such as Rhizobium, associated with leguminous plants.

So, the correct option is 'All of these'.

In the process of nitrification, ammonia is first oxidized to nitrite by

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Nitrosomonas and Nitrosococcus

  2. Nitrosomonas and Nitrobacter

  3. Pseudomonas and Nitrosococcus

  4. Pseudomonas and Thiobacillus

Show answer
Correct Option: A
Explanation:

First step, ammonium ions are oxidised to nitrites. Nitrosomonas  are the  most important agents of oxidation of ammonia to nitrite in soil. Certain other bacteria are Nitrosococcus , Nitrosolobus ,etc.

Second step , oxidation of nitrite to nitrate takes place by Nitrobacter. 
So the correct option is "Nitrosomonas and Nitrococcus".

Which of the following is a symbiotic nitrogen fixer ?

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Azolla

  2. Glomus

  3. Azotobacter

  4. Frankia

Show answer
Correct Option: D
Explanation:
Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. Frankia is a nitrogen-fixing bacterium that lives in the soil and has a symbiotic relationship with many plants. Frankia is a genus of nitrogen-fixing, filamentous bacteria that live in symbiosis with actinorhizal plants, similar to the Rhizobium bacteria found in the root nodules of legumes in the family Fabaceae.

So, the correct answer is 'Frankia'.

Phosphorus is required for better nitrogen fixation by Rhizobium

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. True

  2. False

Show answer
Correct Option: A
Explanation:
Phosphorous plays an important role in the symbiotic association for the natural fixation of the nitrogen in the plants .
Hence the given statement is true .

A nitrogen-fixing bacterium, which forms a loose association with the roots of crop plants (grasses) is

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Azotobacter

  2. Bacillus polymyxa

  3. Clostridium

  4. Azospirillum

Show answer
Correct Option: D
Explanation:
Azospirillum is a free-living nitrogen-fixing bacteria closely associated with crops of grass family
So, the correct answer is 'Azospirillum'

How many organisms In the list given below are $N _2$ fixer autotrophs?
Azotobacter, Chromobum, Azospirillum, Rhodospirillum, Rhizobium, Nitrobacter, Aulosira, Nostoc, Osallatona

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Three

  2. Four

  3. Five 

  4. Six

Show answer
Correct Option: C
Explanation:

Nitrogen-fixing bacteria are capable of fixing atmospheric nitrogen to inorganic substances usable by plants. Example from the given list are Azetobactor, Azospirillum, Rhizobium, Nitrobactor and Nostoc.

So the correct answer is 'five'.

Which of the following is a free living aerobic non - photosynthetic nitrogen-fixer ?

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. $Rhizobium$

  2. $Azotobacter$

  3. $Azospirillum$

  4. $Nostoc$

Show answer
Correct Option: B
Explanation:

Azotobacter is a free-living nitrogen-fixing bacterium, which is used as a biofertilizer in the cultivation of most crops. Azotobacter respires aerobically, receiving energy from redox reactions, using organic compounds as electron donors. Azotobacter can use a variety of carbohydrates, alcohols, and salts of organic acids as sources of carbon. 

Rhizobium fixes nitrogen by symbiotic association. Nostoc is photosynthetic. Azospirillum is anaerobic. 
So, the correct option is 'Azotobacter'.

All of the following statements concerning the actinomycetous filamentous soil bacterium Frankia are correct except that Frankia

zoology bio-geo chemical cycles in nature nitrogen cycle biogeochemical cycles - gaseous nutrient cycles

  1. Can induce root nodules on many plant species

  2. Can fix nitrogen in the free-living state

  3. Like Rhizobium, it usually infects its host plant through root hair deformation and stimulates cell proliferation in the host's cortex

  4. Forms specialized vesicles in which the nitrogenase is protected from oxygen by a chemical barrier involving triterpene hopanoids

Show answer
Correct Option: B
Explanation:

Frankia is a bacterium which grows in a symbiotic association with the roots of non-leguminous plants.  It can fix atmospheric nitrogen. It cannot fix nitrogen in free-living state.

So, the correct option is 'Can fix nitrogen in free-living state'.