Human Reproduction

(d) Seminal plasma is rich in fructose, calcium and certain enzymes that nourish and activate sperms.

(a) Sperm has : (i) head in which acrosome & nucleus are present (ii) middle piece in which it contains many mitochondria (iii) A long & highly motile tail.

(A short neck is also present between middle piece & head which has centrioles and may sometimes regarded as a part of middle piece)

(a) Morula is a solid ball contained within the zone pellucida.

It has almost equal quantity of cytoplasm as an uncleaved zygote but much more DNA.

When the sperm approach the egg, they gets bind to the zona pellucida in a process known as sperm binding.

This triggers the acrosome reaction, in which the enzymes of the acrosome are freed.

These enzymes then begin to digest the zona pellucida and allow the sperm to tunnel toward the egg's plasma membrane.

(b) Vasa efferentia are ductuless leading from rete testis to vas deferens.

The rete testis is an anastomosing network of tubules located in the hilum of the testicles that carries sperm from the seminiferous tubules to the vasa efferentia.

The temperature of the testes is regulated by the scrotum (which expands and contracts to facilitate heat transfer) and heat exchange between blood flowing into the testes via the arteries in the spermatic cord, and that flowing out of the testes via the veins in the spermatic cord.

This results in the pre-cooling of blood entering the testes, although the precooling mechanism can only regulate testicular temperature to an extent.

In situations of extreme heat, the scrotum's natural cooling mechanism is insufficient to prevent a rise in testicular temperature.

The increased testicular temperature may affect both the quality and quantity of the sperm.

(b) Fertilization occurs at the ampullary-isthmic junction of the fallopian tube.

(a) Urethra carries both semen and urine in human males.

(c) Meiosis II completes after sperm entry (at fertilization), forming the mature ovum and second polar body.

(a) Fusion of male and female gamete produces a zygote.

Repeated division of the zygote is called cleavage forming a solid morula.

After further division and rearrangement a fluid filled cavity surrounded by blastomeres - blastula is formed.

The appearance of germ layers mark the gastrula.

(a) After ovulation, follicular cells fill with yellow fluid to form corpus luteum.

(a) A change in the amount of yolk and its distribution in the egg will affect pattern of cleavage.

The pattern of cleavage is influenced by the amount of yolk in the egg.

In eggs with less yolk, cleavages are equal, and the resulting blastomeres are of similar size.

If the yolk is localized, such as in frog eggs, then cleavages are unequal, the cells derived from the yolky region (the vegetal pole) are larger than those derived from the region without yolk (the animal pole).