1. Reproduction in Organisms(12)

Cellular differentiation is the process by which a cell changes from one cell type to another. Usually, this is because a less specialised type becomes a more specialised type, such as during cell growth.

Apogamy was first reported by Farlow (1874). It can be defined as the development of a sporophyte directly from the gametophyte without the intervention of sex organs and gametes

Tapetum is the innermost layer of the wall of pollen sac. The tapetum is nutritive in function. The tapetal cells are multinucleate and contain Ubish bodies.

Root is the main plant body and it isalways diploid (2n).

Pollination by wind (anemophily) is more common amongst abiotic pollinations. It is quite common in grasses.
 

In embryo sac of angiosperm, egg apparatus occurs towards micropylar pole and generally organises by
two synergids and one egg cell. Egg cell has a large vacuole at its upper end and a prominent nucleus near its
lower end. Synergids show a filiform apparatus attached to their upper wall. It is known to attract and guide
the pollen tube. Each of the synergids has a vacuole at its lower end and the nucleus at its upper end.
 

When the somatic cells are cultured and the culture is made stationary, each cell starts differentiating into an
independent embryo showing all the stages of embryo development. These embryos are called embryoids,
which can give rise to a complete plant.

Allogamous pollination performed by birds is called omithophily. Entomophily is pollination carried out by
insects.

Seminiferous tubules are located within the testes, and are the specific location of meiosis, and the subsequent creation of gametes, namely spermatozoa.

Fertilization membrane is the membrane that forms around a fertilised ovum and prevents penetration by additional spermatozoon.

The gestation period of a human, from time of conception to birth is approximately 9 months (266 days/38 Weeks). It is calculated from the first day of the last menstrual period.

AIDS is caused by Human Immunodeficiency Virus (HIV).

Telolecithal also known as macrolecithal, refers to the uneven distribution of yolk in the cytoplasm of ovums found in birds, reptiles, fish, and monotremes. Mesolecithal eggs have comparatively more yolk than the microlecithal eggs. The yolk is concentrated in one part of the egg (the vegetal pole), with the cell nucleus and most of the cytoplasm in the other (the animal pole).

In all bilaterian animals, the mesoderm is one of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and endoderm (inside layer), with the mesoderm as the middle layer between them.The mesoderm forms mesenchyme (connective tissue), mesothelium, non-epithelial blood cells and coelomocytes. Mesothelium lines coeloms; forms the muscles in a process known as myogenesis, septa (cross-wise partitions) and mesenteries (length-wise partitions); and forms part of the gonads (the rest being the gametes)

Fact

an acute rise of LH ("LH surge") triggers ovulation and development of the corpus luteum. In males, where LH had also been called interstitial cell-stimulating hormone (ICSH),

During cleavage the volume of cytoplasm is increased.

The macromeres contain the largest amount of yolk but micromeres contain no yolk.

Acrosome is a cap-like structure derived from the Golgi apparatus.

Secondary spermatocytes are haploid whereas primary spermatocytes are diploid.