Biology Test 324

In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water), i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation.

Pollination by wind is called anemophily and such plants in which pollination occurs by wind are called anemophilous plants. Anemophilous plants are characterized by small flowers, pollens present in large numbers which are small, dry and light in weight. Numerous ovules are generally reduced in the ovary and they have feathery or brushy stigma (to receive the pollen). Grasses and palms are generally anemophilous.

Pollination is the transfer of pollen grains from the anther of one flower to the stigma of a pistil of either the same flower or some other flower of the same species.

Flowering plants have an array of adaptations to achieve pollination.

1. Autogamy is a type of when only one flower is involved. Thus, the pollen of the anther of a flower is set on the stigma of the same flower. Complete autogamy is seen in Cleistogamous flowers, which do not open at all (like Commelina). Chasmogamous flowers, which opens, may also show autogamy (like Pea).

2. Geitonogamy is a condition in which pollen of one flower is shed on the stigma of another flower of the same plant. Geiton means neighbour. Ecologically, this needs some agents, so it is a type of cross pollination. But physiologically and genetically, it is autogamy, since the genetics is identical.

3. Xenogamy is the perfect cross-pollination, which is also called Allogamy. In this case, two plants are involved along with some agents to transfer the pollen.

Both Geitonogamy and Allogamy (= Xenogamy) need external agents for pollen to be transferred.

Angiosperms are known to use several agents for pollination, both Biotic and Abiotic.

A. Abiotic agents like Wind (Anemophily) and Water (Hydrophily) are used to pollinate.

B. Biotic agents can be:

I. Bees, Butterfly, Moth (Entomophily) as in Sunflower.

II. Bat (Chiropterophily) as in Adansonia digitata.

III. Bird (Ornithophily) as in Callistemon.

IV. Snail (Melacophily) as in Aresaema.

V. Ants (Myrmecophily) as in some Orchids.

Apomixis is the production of seeds without fertilization. Normally, in sexual reproduction, the sperm nuclei fuse with egg cell and polar nuclei in angiosperms. This results in the formation of a diploid zygote and triploid primary endosperm nucleus. On ripening of ovules, seeds are formed and ripening of ovary form the fruit.

In apomixis, seed production takes place without the fertilization of egg cell and the sperm nucleus. All the seeds formed through apomixis are genetically similar. Apomixis is an asexual method of reproduction. Seed formation takes place without zygote formation.

Pollination is the transfer of the male part of the plant to the female part of the plant that enables fertilization and production of seed and fruits. Pollen grains are responsible for pollination and are found only in gymnosperms and angiosperms. Hence, pollination occurs in these.

Kingdom Monera consists of prokaryotic organisms, which means they have a simpler cell structure without a true nucleus or nuclear membrane, making Option c incorrect. Monerans can have a cell wall, lack a nuclear membrane, and exhibit a cellular level of body organization, which aligns with Options A,B, and D.

Continued self-pollination result in inbreeding depression. Flowering plants have developed many devices to discourage self-pollination and to encourage pollination.

In some species, pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma become receptive or stigma becomes receptive much before the release of pollen another species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy.

The third device to prevent inbreeding is self-incompatibility. That is a genetic mechanism and prevents self-pollination from the same flower or other flowers of the same plant).

In angiosperms, one male gamete fuses with the egg resulting in the formation of a diploid zygote. The other male gamete fuses with the two polar nuclei forming the primary endosperm nucleus. This type of fertilization is called double fertilization.

Inside the ovary, there is an ovule present that develops into female reproductive cells. The ovule structure is made up of three parts: the outer layer is called integument, inside the integument, the nucellus is present that provides nourishment to the embryo, in the centre, there is female gametophyte present. In anatropous, the body of the ovule becomes inverted—the integument, nucellus, and chalaza located parallel to the funiculus. Micropyle in the anatropous ovule is located near the hilum.

The production of fruits without seeds is called parthenocarpy. Tools for obtaining parthenocarpic fruits are becoming increasingly important because

(i) Seeds are irritants during the eating of the fruit.

(ii) Processing of fruits by the food industry requires the removal of seeds which is quite difficult. Therefore, seedless fruits are preferred by the food industry.

(iii) There is an increasing tendency to grow fruit-bearing plants inside greenhouses. Reliable insect pollinators cannot be ensured in every case. Now in the case of pomegranate, we have seeds as their edible part. If we produce them via parthenocarpy, we do not get the seed and its a waste of this process