2. Sexual Reproduction in flowering plants(12)

Polyspory is the occurrence of more than four spores from a spore mother cell.

In angiosperms (dicots), the Polygonum type of embryo sac is the most common. In this embryo sac, the arrangement of the nuclei is 3 + 2 + 3, i.e. 3 in antipodal cells, 2 in polar nuclei (which later fuse and form a diploid secondary nucleus) and 3 in egg apparatus (2 in synergids and 1 in egg cell).

Double fertilisation was discovered by S. G. Nawaschin (1897) in Lilium and Fritillaria species.

In angiosperms, male gametophyte consists of a tube cell and a generative cell. The generative cell divides to form two male gametes.

Central cell is the largest cell of embryo sac and is the mother cell of endosperm. The enlargement of the embryo sac after the last nuclear division is largely due to inflation of the large central vacuole of central cell.

Micropyle is the narrow passage left by the integuments at one end of the ovule. It allows the entry of pollen tube into the ovule. This phenomenon is known as porogamy. For example, lily.

Pollen grain is the mother cell of male gametophyte. Development of male gametophyte begins inside themicro sporangium. The microspore nucleus divide mitotically to form a smaller generative cell and a much larger, vegetative cell (tube cell). The generative cell produces two male gametes, whereas, the vegetative cell form pollen tube after pollination. Pollen grain contains two cells, i.e., tube cell and generative cell at the time of pollination.

This is an incorrect option as pollen wall does not have cavities containing proteins.

According to Farmer and Moore, four daughter cells are formed from single cell in meiosis. As a result ofmicrosporogenesis (meiotic division) in four microspore mother cells, 16 pollen grains will be produced.

Syngamy is the fusion of gametes, i.e., the union of nuclei of male gamete and female gamete in theprocess of reproduction. In angiosperms, generative fertilization is also called, syngamy.

Cross pollination is the transfer of pollen grains of a male flower to the stigma of female flower, which occurs either on the same plant (monoecious) or on the different plant (dioecious).

In orthotropous (atropous) ovule, the micropyle, funicle and chalaza lie in a straight line.

Parthenogenesis is the development of an embryo from an unfertilised egg or if a spermatozoan does penetrate the egg, there is no union of male and female pronuclei. It is found in many plants (dandelions and hawk weeds) and animals (aphids and honey bees).

The movement of pollen tube towards embryo sac is chemotropism as it occurs in responce to certainchemical substances like auxin and carbohydrates.

Double fertilisation is the unique feature of flowering plants, whereby from a single pollen grain, the two sperm nuclei within the pollen tube fuse with different nuclei within the embryo sac of the ovule. Fusion of one sperm with egg cell nucleus forms zygote and the fusion of other sperm with diploid secondary nucleus forms triploid primary endosperm nucleus.

In angiosperms, endosperm is triploid and secondary nucleus (2n) is diploid.

Unisexuality of flowers prevents autogamy (self pollination) but not geitonogamy (pollination betweenseparate male and female flowers on the same plant).

In angiosperms, one male gamete fuses with the egg to form the diploid zygote. The process is called syngamy. The other male gamete fuses with the two polar nuclei to form triploid primary endosperm nucleus. The process is called triple fusion. These two acts of fertilization constitute the process of double fertilization.

Sugarcane is cultivated through stem cutting.

In porogamy, pollen tube enters the ovule through the micropyle. It is the most common way of the entry of pollen tube inside ovule.