Structure of Pollen Grain

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Structure of Pollen Grain is considered one of the most asked concept.
20 Questions around this concept.

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DIFFICULT

In the following questions, a statement of assertion (A) is followed by a statement of reason (R)

(1) If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark A

(2) If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark B

(3) If Assertion is true statement but Reason is false, then mark C

(4) If both Assertion and Reason are false statements, then mark D

Assertion: Overall, the exact size of pollen grain size ranges between 25-50 micrometres or microns.

Reason: The shape of the pollen grain is commonly found in round, ovule, triangular, disc or in a bean-shape with a smooth to spiky texture.

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Concepts Covered - 1

Structure of Pollen Grain

The pollen grains represent the male gametophytes.
Pollen grains are generally spherical measuring about 25-50 micrometres in diameter.
It has a prominent two-layered wall.
The hard outer layer called the exine is made up of sporopollenin which is one of the most resistant organic materials known.
It can withstand high temperatures and strong acids and alkali.
No enzyme that degrades sporopollenin is so far known.
Pollen grain exine has prominent apertures called germ pores where sporopollenin is absent.
Pollen grains are well preserved as fossils because of the presence of sporopollenin.
The inner wall of the pollen grain is called the intine.
It is a thin and continuous layer made up of cellulose and pectin.
In insect-pollinated pollen grains, the exine is spiny as well as covered by a yellowish, viscous sticky and oily layer called pollenkitt.
Pollen grains of many species cause severe allergies and bronchial afflictions in some people often leading to chronic respiratory disorders– asthma, bronchitis, etc.
Parthenium or carrot grass came into India as a contaminant with imported wheat has become ubiquitous in occurrence and causes pollen allergy.
Pollen grains are rich in nutrients.
It has become a fashion in recent years to use pollen tablets as food supplements.
In western countries, a large number of pollen products in the form of tablets and syrups are available in the market.
Pollen consumption has been claimed to increase the performance of athletes and racehorses.
The period for which pollen grains remain viable is highly variable and to some extent depends on the prevailing temperature and humidity.
In some cereals such as rice and wheat, pollen grains lose viability within 30 minutes of their release, and in some members of Rosaceae, Leguminosae and Solanaceae, they maintain viability for months.
It is possible to store pollen grains of a large number of species for years in liquid nitrogen ( $-196^{^{o}}C$ ).
Such stored pollen can be used as pollen banks, similar to seed banks, in crop breeding programmes.