Q. (a) Why is it not possible to reconstruct the whole organism from a fragment in complex multicellular organisms?
(b) Sexual maturation of reproductive tissues and organs are necessary link for reproduction. Elucidate.
Ans: (a) The reason is that many multi-cellular organisms are not simply a random collection of cells. Specialised cells are organised as tissues, and tissues are organised into organs, which then have to be placed at definite positions in the body. Therefore, cell-by-cell division would be impractical.
(b) Sexual maturation of reproductive tissues is a necessary link for reproduction because of the need for specialised cell called germ-cells to participate in sexual reproduction. The body of the individual organism has to grow to its adult size, the rate of general body growth begins to slow down, reproductive tissues begin to mature.
A whole new set of changes in the appearance of the body takes place like change in body proportions, new features appear. This period during adolescence is called puberty.
There are also changes taking place that are different between boys and girls. In girls, breast size begins to increase, with darkening of the skin of the nipples at the tips of the breasts. Also, girls begin to menstruate at around this time. Boys begin to have new thick hair growth on the face and their voices begin to crack.
Q. (a) How are variations useful for species if there is drastic alteration in the niches?
(b) Explain how the uterus and placenta provide necessary conditions for proper growth and development of the embryo after implantation?
Ans: (a) If the niche were drastically altered, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Variation is thus useful for the survival of species over time.
● The lining of the uterus thickens and is richly supplied with blood to nourish the growing embryo.
● The embryo gets nutrition from the mother’s blood with the help of placenta. It is embedded in the uterine wall.
● It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi.
● This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta.
● The child is born as a result of rhythmic contractions of the muscles in the uterus.