Sexual Reproduction in Flowering Plants Test - 6

In some flowers, there is no distinction of sepals and petals. In these flowers these non-essential organs are together called as perianth. The individual parts of perianth are called tepals.

In hypogynous flowers thalamus is convex or conical, ovary at the top and other floral organs below the ovary. Such flower are also called as ovary superior as in Mustard and Brinjal flowers.

Aestivation is the arrangement of accessary floral organs in relation to one another in the bud condition. Activation may be open, valvate, twisted and imbricate.

Actinomorphic flowers have radial symmetry. It is regular in arrangement and two equal halves are formed by any vertical division passing through the centre. Hence, only statement a is correct.

In Epigynous flower, the other floral organs are borne at the top of the ovary and ovary is below. Hence they are called ovary inferior while other floral parts are superior to ovary.

The mature anther consists of four microsporangia which contain four layers. The inner most layer is called tapetum that provide nutrient to growing microspores and tissues inside it are called microspore mother cell that produce pollen grain.

Each microspore mother cell produces four pollen grains by reduction division. Hence to produce 64 pollen grains 16 meiotic or reduction division is required.

Filiform apparatus is finger-like projection attached with egg apparatus. This apparatus guide the pollen tube carrying male gametes for facilitating Syngamy.

Each Sporogenous cell under meiotic division to form tetrad of megaspores. The three megaspores degenerate and only one megaspore develops into embryo sac or female gametophyte.

Microsporangium is surrounded by four wall layers. The innermost layer is tapetum. Tapetum nourishes the developing pollens. The three outer walls provide protection and help in dehiscence of anther to release pollen grains.

Each microspore mother produces 4 pollen grains by reduction division. Bilobed dithecious have four microsporangium.

Therefore,

50 x 4 x 4

= 800 male gametes are formed.

Pollen grain consists of hard covering of exine but their viability may lost with time. For Hybridisation pollen grains are collected and stored in liquid nitrogen below -196 degree Celsius temperature.

Inbreeding occurs in intraspecific flowers as contain same kinds of genetic materials. Outbreeding takes place between interspecific flowers having different kinds of genetic materials.

Self-pollination involves transfer of pollen grain from anther to stigma of same flower. The two fusing gametes are genetically similar to each other as they are produced by same plant. Continued self –pollination results into pure line and breeding depression.

Large amount of fossilized pollen grain are found during excavation process of older parts due to tough covering of Sporopollenin that make the outer wall of pollen grain, exine. This substance cannot be hydrolyzed by any enzyme known.

The zygote divides mitotically many times to form large number of cells. These cells arrange into different shape. The most common embryo is Globular embryo.

Zygote may divides into two or more parts to develop multiple embryos. The formation of more than one embryo inside the same ovule by cleavage is called cleavage polyembryony.

Endosperm cells are triploid as they are formed by triple fission of two polar nuclei and one male gamete. So, haploid cell will contain 8 chromosomes only. Root cells are diploid. Hence root cell will contain 16 chromosomes.

The meiocytecell are diploid so, haploid cell will contain 16 chromosomes. The endosperm cell are formed by fusion of two polar nuclei and one male gametes so, endosperm cells are triploid that will contain 16x3= 48 chromosomes.

Embryo of certain monocotyledonous seeds contain additional cotyledon besides one present in al monocots. This cotyledon represents the evolutionary stage of cotyledon formation from one to two.

The female gametophyte (embryo sac) develops from a single functional megaspore. This megaspore undergoes three successive mitotic divisions to form eight nucleate embryo sacs.

The first mitotic division in the megaspore forms two nuclei. One nucleus moves towards the micropylar end while the other nucleus moves towards the chalazal end. Then, these nuclei divide at their respective ends and re-divide to form eight nucleate stages. As a result, there are four nuclei each at both the ends i.e., at the micropylar and the chalazal end in the embryo sac. At the micropylar end, out of the four nuclei only three differentiate into two synergids and one egg cell. Together they are known as the egg apparatus. Similarly, at the chalazal end, three out of four nuclei differentiates as antipodal cells. The remaining two cells (of the micropylar and the chalazal end) move towards the centre and are known as the polar nuclei, which are situated in a large central cell. Hence, at maturity, the female gametophyte appears as a 7-celled structure, though it has 8 nucleate.

Crop improvement programme is carried out to obtain crops with desired traits that may be more yields, resistance to disease, higher nutrient value etc. Two plants having desired traits are hybridized to obtain combination of desired traits.

Embryogeny in dicotyledonous plants involves mitotic division of zygote to form proembryo, further division in proembryo results into globular embryo followed by heart-shaped embryo to mature embryo.

The number of ovule present in ovary determine the number of seeds produced inside the fruit. Mango and neem produce single seed in each fruit. Lemon contain a number of seeds but orchid contain many small size seeds.

Dormancy is the state of state of inactivity during which metabolic process slows down. Seed may remain viable to several months to years depending upon type of seeds and condition.