Advantages of asexual reproduction:
1.      It is faster and easier than sexual reproduction because only one organism is involved.
2.      Since the animal or pollen grain doesn’t have to travel in order to propagate the species, it can conserve energy.
Disadvantagesof asexual reproduction:
1.      Evolutionary change is not possible due to lack of variations.
2.      Any genetic defect in the parent organism is also inherited in the offspring.

Plant embryogenesis begins with an asymmetric cell division, resulting in a smaller apical (terminal) cell and a larger basal cell. This first asymmetric division provides polarity to the embryo. Most of the plant embryo develops from the apical (terminal) cell. The suspensor develops from the basal cell. The suspensor anchors the embryo to the endosperm and serves as a nutrient conduit for the developing embryo.

Further cell division leads to the globular stage. The three basic tissue systems (dermal, ground, and vascular) can be recognized at this point based on characteristic cell division patterns. The globular shape of the embryo is then lost as the cotyledons (embryonic leaves) begin to form. The formation of two cotyledons in dicots gives the embryo a heart-shaped appearance. In monocots, only a single cotyledon forms.

Upright cotyledons can give the embryo a torpedo shape, and by this point the suspensor is degenerating and the shoot apical meristem and room apical meristem are established. These meristems will give rise to the adult structures of the plant upon germination. Further growth of the cotyledons results in the torpedo and walking-stick stages. At this point, embryogenesis is arrested, and the mature seed dessicates and remains dormant until germination.

• A nucleoside has a chemical composition that consists of a sugar and a base without the phosphate group.
• They are used as agents in medicine that are primarily used against viruses and cancer causing agents.
• Some of the key examples of nucleosides are the same as nucleotides only with the addition of phosphate groups.

Transfer of pollen grains from anther to stigma is termed as Pollination. This transfer of pollen grains occurs with the help of pollinating agents like wind, water, insects, birds etc.

There are different types of pollination:

Autogamy

• Transfer of pollen grains from anther to stigma of the same flower
• Seen in plants which produce Chasmogamous & Cleistogamous flowers
• Chasmogamous flowers : Exposed anther & stigma
• Cleistogamous flowers : Closed flower. Anther & stigma lie very close to each other. Example: Viola, polygala

Geitonogamy

• Transfer of pollen grains from anther to stigma of another flower of same plant
• It is functionally cross-pollination, but genetically self-pollination

Xenogamy

• Transfer of pollen grains from anther to stigma of a different plant
• Genetically as well as functionally cross-pollination

Two haploid spermatids (haploid cells) are generated by each secondary spermatocyte, resulting in a total of four spermatids. Spermiogenesis is the final stage of spermatogenesis, and, during this phase, spermatids mature into spermatozoa (sperm cells) There are three steps in spermatogenesis: 1) meiosis, during which the number of chromosomes in the cell is reduced to half or 23 chromosomes each; 2) meiosis II, during which each haploid cell forms spermatids; and 3) spermiogenesis, during which each spermatid develops into a sperm cell with a head and tail.

Cleistogamy is the phenomenon, where flowers never open and in such flowers, only self-pollination occurs within the bud (unopened flower). Bisexual flowers which do not open at all are called cleistogamous. In such flowers, anthers and stigma lie close to each other. When the anthers dehisce in the flower buds, pollen grains come in contact with the stigma and pollination occurs. Cleistogamous flowers are not dependent on external agencies for pollination. Hence, seed setting is not dependent on pollinators.

Hence, assured seed set is possible even in the absence of pollinators when the flower is Cleistogamous.

Features of water pollinated flowers:

• They produce a large number of pollens because most of them get lost by the flow of water.
• The stigmas are large and feathery to catch the pollens.
• The male flowers after maturation get detached from the plant and float above the water surface.
• The stalks of the pollinated flowers are usually very long to project their stigmas above the water surface.
• No animal transporters are needed for pollination.
• The flowers need not be colourful (no need to attract) and generally white in colour.

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are called gonadotropins because stimulate the gonads - in males, the testes, and in females, the ovaries. ... These two hormones are secreted from cells in the anterior pituitary called gonadotrophs. Follicle-stimulating hormone (FSH) is a glycoprotein gonadotropin secreted by the anterior pituitary in response to gonadotropin-releasing hormone (GnRH) released by the hypothalamus. The pituitary gland also secretes luteinizing hormone (LH), another gonadotropin. In females, FSH stimulates the development of egg cells, called ova, which develop in structures called follicles. LH also plays a role in the development of ova, induction of ovulation, and stimulation of estradiol and progesterone production by the ovaries.

Homozygous is a condition in which a gene possesses a pair of the same alleles (TT or tt) for a single characteristic. This is the homozygous condition for the character, tallness. Plants are either completely tall or completely short.

The formation of nearly asleep and inactive forms of bacteria is known as Sporulation. Spores can preserve the bacteria’s genetic material when the conditions are harsh and difficult for the normal form of bacteria.

Sporulation provides a multilayered structure that can be maintained for a long time. Spores are designed to protect a bacterium from dryness, heat, and intense radiation for a long time, relative to the normal life span of the microorganism. Endospores of Bacillus subtilis have been recovered from substances that are thousands of years old. Also, these are capable of resuscitation into a healthy and dividing cell. There has been a recovery of spores from amber that is more than 250 million years old.