NEET Practice Questions (MCQs) with Answers & Solutions

Pollination by wind (anemophily) is more common amongst abiotic pollinations. Wind pollination is quite common in grasses.

Occurrence of more than one embryo in a seed is referred as polyembryony. In many Citrus and mango varieties, some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos in such species each ovule contains many embryos (nucellar polyembryony).

Bisexual flowers which remain always closed are called cleistogamous and such condition of flowers is called cleistogamy. In such flowers, the anthers and stigma lie close to each other. When anthers dehisces in the flowers buds, pollen grains come in contact with stigma to effect pollination. Thus, cleistogamous flowers are invariable autogamous.

Geitonogamy (Greek geiton = neighbour and gameiu = to marry) involves the transfer of pollen grains from a male flower to the stigma of another female flower originating on the same plant. Thus, geitonogamy operates only in monoecious plants, ie, plants having male and female flowers on different places but on the same plant, eg, maize (Zea mays). In animal pollinated system, this is accomplished by a pollinator visting multiple flowers on the same plants. It is also possible within species that are wind pollinated.

Pollination taking place by means of wind is known as anemophily, eg, Zea mays, Cannabis, Pinus, etc. Some features of wind pollinated flowers are -

(i) Non-essential whorls such as calyx, corolla and bracts, bracteoles are not showy.

(ii) The perianth lobes are undeveloped or reduced and sometimes absent.

(iii) Flowers are devoid of scent and nectars.

(iv) Plants produce a very large quantity of dusty pollen grains.

(v) Pollen grains are dry, very small sized, non-sticky and unwettable

These feature are helpful for individuality of pollen grains.

Pinus is monoecious, which bear male cone as well as female cone on the same tree on separate branches. Marchantia Cycs and papaya are dioecious plants.

In angiosperms a single diploid megaspore mother cell matures within an ovule. Through meiosis it gives rise to four megaspores (haploid). In most plants only one of these megaspores survive. This functional megaspore divides three times by mitosis and produces eight haploid nuclei enclosed within a 7-celled embryo sac. One nucleus is located near the opening of embryo sac in egg cell. Two nuclei are located in a single cell in the middle of embryo sac and are called polar nuclei, two nuclei are contained in cells called synergids that flank the egg cell and other three nuclei are resided in the cells called antipodals, located at the end of embryo sac, opposite the egg cell.

Nucellus is centrally located mass of thin-walled parenchymatous cells covered by integuments in ovule.

Endosperm, if present acts asthe food storage tissue of a seed. The seeds with endosperm are called endospermic or albuminous (eg, Cocos nucifera, Ricinus communis, Zea mays and other cereals, while those without endosperm are called non-endospermic or ex-albuminous seeds (eg, Brassica campestris, Arachis hypogea, Pisum sativum).

In castor (Ricinus communis) the endosperm is whitish soft mass rich with oily reserve food material. 

The endosperm in maize is yellowish in colour, the outermost layer of endosperm is called aleurone layer, which is rich in protein.

The transfer of pollen from anther to stigma is called pollination. Autogamy also called self-pollination inovlves the transfer of pollen grains of one flower to the stigma of same flower. Self-pollination occurs only in bisexual or hermaphrodite flowers.

Geitonogamy inovlves the transfer of pollen grains from a male flower to stigma of female flower of same plant. Thus, geitonogamy operates only in monoecious plants, i.e., the plants having male and female flowers on different places.

Allogamy or xenogamy also known as cross-pollination involves the transfer of pollen grains of male flower to teh stigma of genetically different female flower. It takes place via various agencies like wind, water, insects etc.

The pollen wall is consisted of two layers the outer exine and inner intine The exine is chiefly made up of sporopollenin, which is derived by the oxidative polymerization of carotenoids. Sporopollenin is one of the most resistant biological matterials known. Exine is thin in begining but becomes very thick with maturity.

During secondary growth in extrastelar region cork cambiumor phellogen cells divide periclinally, cutting off cells towards the outside and inside. The cells cutoff towards outside become suberised and dead and form cork. Cork is impervious to water due to suberin and provides protection to underlying tissues.