(4)

Vallisneria is a water-pollinated plant, therefore flowers are neither colourful nor produce nectar for pollination. These characters are attributed to insect pollinated flowers.

(1)

The given figure represents a compact inflorescence with well-exposed stamens of wind-pollinated plant.

(4)

In some members of Families Rosaceae, Leguminosae and Solanaceae, pollen grains maintain viability for months.

(1)

Geitonogamy involves transfer of pollen grains from the anther to the stigma of another flower of the same plant. Autogamy is a type of self-pollination in which an intersexual or perfect flower is pollinated by its own pollen, i.e., it involves the transfer of pollen grains from anther to stigma of the same flower. Xenogamy involves transfer of pollen grains from anther to the stigma of a different plant. Cleistogamy is a phenomenon in which flowers do not open at all, therefore show self-fertilisation and autogamy.

(4)

The sequence of events in formation of female gametophyte in the ovule in an angiosperm is as follows:
(i) Megaspore mother cell or megasporocyte is a diploid (2n) cell which undergoes meiosis to form a linear tetrad of four haploid megaspores (n).

(ii) Normally, the chalazal megaspore is the functional megaspore while the other three degenerate. The functional megaspore is the first cell of female gametophyte.

(iii) The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. These mitotic divisions are strictly free nuclear, which means nuclear divisions are not followed immediately by cell wall formation.

(iv) Out of 8 nuclei, 4 nuclei are arranged at each pole. One nucleus from each pole migrates to the centre to form two polar nuclei. Cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac with 7-cells.

(4)

The tassels in the corn cob are stigma and style that wave in the wind to trap pollen grains.

(3)

(4)

Among the animals, insects, particularly bees are the dominant biotic pollinating agents.

(2)

(2)

A typical angiosperm embryo sac is 7 celled and 8 nucleate structure.

(1)

In some members of families Rosaceae, Leguminosae and Solanaceae, pollen grains maintain viability for months.

(4)

(1)

In many aquatic plants with emergent flowers, pollination occurs by wind or insects, e.g., lotus, water lily, water hyacinth.

(2)

(4)

In Vallisneria, the female flower reaches the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water. They are carried passively by water currents, some of them eventually reach the female flowers and the stigma.

(2)

(3)

Pollen grains can be stored for several years in liquid nitrogen at -196°C. This is also known as cryopreservation.

(4)

Exine of pollen grain is made up of highly resistant fatty substance called sporopollenin, which is not degraded by any enzyme. It is not affected by high temperature, strong acid or strong alkali. Because of the sporopollenin, pollen grains are well preserved as microfossils.

(4)

Each pollen grain of Pinus has two wing like structures which enable it to float in air, as an adaptation for dispersal by wind. Pollen grains of mustard, Cycas and mango are not winged.

(2)

In angiosperms, the functional megaspore is the first cell of female gametophyte. It enlarges and undergoes three nuclear mitotic divisions to form embryo sac.

(1)

Entomophily is the most common type of zoophily where pollination takes place through the agency of insects. Entomophilous flowers are brightly coloured and secrete nectar to attract visiting insects.
Anemophily (wind pollination) and hydrophily (water pollination) do not require attractants or rewards due to the involvement of abiotic pollinating agents. Cleistogamy is self-pollination in closed flowers.

(2)

Single ovule in the ovary and flowers packed into inflorescence are characteristics of wind pollinated flowers.

(1)

Dioecious plants are those plants in which male flowers and female flowers are borne on different plants. Therefore, they prevent both autogamy and geitonogamy.

(3)

(2)

(1)

The ovule of an angiosperm is equivalent to integumented megasporangium.

(3)

Tapetum is the innermost wall layer of microsporangium that nourishes developing pollen grains.

(3)

Pollen-pistil interaction is the group of events that occur from the time of pollen deposition over the stigma to the time of pollen tube entry into ovule. It is a safety measure to ensure that illegitimate crossing does not occur. Pollen grains of number of plants may settle over a stigma. The pollens belonging to same species would germinate while other fail to do so, but the pollen tube of the compatible pollen will grow through the style to reach the ovule whereas growth of incompatible pollens will be arrested at stigmatic disc or sometimes in the beginning part of style.

(2)

(2)

Filiform apparatus is a mass of finger-like projections of the wall into the cytoplasm. It is present in synergids (help cells) of the embryo sac, in the micropylar region. It guides the pollen tube inside the ovule towards the embryo sac.