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Mineral Nutrition · Question 45

AIPMT 2004MCQMedium📈 Topic in 25% papers+4−1
1

If by radiation all nitrogenase enzymes are inactivated, then there will be no

  1. fixation of nitrogen in legumes
  2. fixation of atmospheric nitrogen
  3. conversion from nitrate to nitrite in legumes
  4. conversion from ammonium to nitrate in soil.

Answer

(1) fixation of nitrogen in legumes

Solution

As per NCERT, the enzyme nitrogenase is present exclusively in prokaryotes; it catalyses the conversion of atmospheric N2 to NH3:

N N Nitrogenase NH3

∵ In legumes, N2 is fixed by Rhizobium inside the root nodules with the help of nitrogenase (protected by leg-haemoglobin).

⇒ If all nitrogenase is inactivated, nitrogen fixation in the root nodules of legumes stops.

∵ Nitrate → nitrite (nitrate reductase) and ammonium → nitrate (nitrification by Nitrosomonas / Nitrobacter) do not need nitrogenase, they continue.

∴ There will be no fixation of nitrogen in legumes.

Answer: (1)

Out of syllabusAIPMT 2004

Keep practising — Mineral Nutrition

2

Plants deficient of element zinc, show its effect on the biosynthesis of plant growth hormone

  1. auxin
  2. cytokinin
  3. ethylene
  4. abscisic acid.
AIPMT 2003
3

Gray spots of oat are caused by deficiency of

  1. Cu
  2. Zn
  3. Mn
  4. Fe
Out of syllabusAIPMT 2003
4

Boron in green plants assists in

  1. activation of enzymes
  2. acting as enzyme co-factor
  3. photosynthesis
  4. sugar transport
Out of syllabusAIPMT 2003
5

Enzyme first used for nitrogen fixation

  1. nitrogenase
  2. nitroreductase
  3. transferase
  4. transaminase
AIPMT 2001
6

Passive absorption of minerals depends on

  1. temperature
  2. temperature and metabolic inhibitor
  3. metabolic inhibitor
  4. humidity
Out of syllabusAIPMT 2001
7

Roots of which plant contain a red pigment which has affinity for oxygen?

  1. Carrot
  2. Soybean
  3. Mustard
  4. Radish
Out of syllabusAIPMT 2001
8

Mg is a component of

  1. chlorophyll
  2. cytochrome
  3. haemoglobin
  4. haemocyanin
Out of syllabusAIPMT 2000
9

Plants take zinc in the form of

  1. ZnSO4
  2. Zn2+
  3. ZnO
  4. Zn
Out of syllabusAIPMT 2000
10

When the plants are grown in magnesium deficient but urea rich soil, the symptoms expressed are

  1. yellowish leaves
  2. colourless petiole
  3. dark green leaves
  4. shoot apex dies
Out of syllabusAIPMT 2000

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