Question

Answer the following questions in short.
a. Explain with examples types of asexual reproduction in unicellular organism.
b. Explain the concept of IVF.
c. Which precautions will you follow to maintain the reproductive health?
d. What is menstrual cycle? Describe it in brief.

Answer 1

a. Asexual reproduction in unicellular organisms can be of three types:

Binary fission: Binary fission is the splitting of parent organisms into two halves, each of which develops to form a complete daughter cell. For example, Amoeba reproduces asexually by the process of binary fission. In Amoeba,binary fission begins with the division of the nucleus. This is followed by the division of the cytoplasm and the cell. Each part receives a portion of the nucleus. Finally, two cells are formed from one parent Amoeba.

Multiple fission − Multiple fission is also seen in Amoeba. In this method, the parent microbe divides into many daughter microbes. Amoeba shows multiple fission under adverse conditions. It covers itself in a protective covering and forms a structure known as cyst. Inside the cyst, the nuclei undergo repetitive nuclear division followed by cytoplasmic division and result in the formation of amoebules. These amoebules are released together when the conditions turn favourable.

Budding − In this method, a bud develops as an outgrowth from parent body. This developing bud detaches from the parent body and the daughter individual develops further. For example, yeast reproduces asexually through the method of budding. During this process, small bulb-like projections (called buds) start coming out of the yeast cell. These buds gradually grow in size and get detached from the parent cell to form a new yeast cell. The new yeast cell then grows and becomes mature to form more yeast cells.

b. Many couples all over the world are unable to produce children due to various reasons. These couples can be assisted to have children through techniques called assisted reproductive technologies (ART). IVF is one such form of ART which includes different methods that can be a boon for childless couples:

Surrogacy- This is a technique which is used for women who face problem in implantation of embryo in uterus. In this technique the donor of the oocyte is the women itself who has problem in implanting the embryo in the uterus. The collected oocyte is fertilized with the sperm of her husband in a test tube. The embryo which is obtained after fertilization is implanted in the uterus of another female who is called the surrogate mother.

ZIFT − It stands for zygote intra fallopian transfer. In ZIFT, the sperm from a donor male and the ova from a donor female are fused in the laboratory. The zygote so formed is transferred into the fallopian tube at the 8 blastomeres stage.

IUT − It stands for intra uterine transfer. In this technique, embryos with more than 8 blastomeres are transferred into the uterus.

GIFT − It stands for gamete intra fallopian transfer. In GIFT, females who cannot produce ovum, but can provide suitable conditions for the fertilisation of ovum, are provided with ovum from a donor.

ICSI − It stands for intra cytoplasmic sperm injection. In this method, sperm is directly injected into the cytoplasm of the ovum.

Artificial insemination − In this technique, the semen collected from the husband or a donor is injected into the vagina or uterus. This cures the infertility arising from the inability of the male partner to ejaculate, or due to low sperm count.


c. Precautions which should be taken in order to maintain good reproductive health are:

• eat a balanced and nutritional diet
• maintain personal hygiene
• take adequate physical exercise
• avoid taking any drugs

d. Menstrual cycle is the reproductive cycle in all primates and begins at puberty (menarche).

• In human females, menstruation occurs once in 28 to 29 days. The cycle of events starting from one menstruation till the next one is called the menstrual cycle.

• During the middle of the menstrual cycle, one ovum is released (ovulation).

• The cycle starts with the menstrual flow (3 to 5 days), caused due to the breakdown of the endometrium of the uterus. Blood vessels in liquid state are discharged, but this occurs only when the ovum is not fertilised.

• It is followed by the follicular phase. In this phase, the primary follicles mature into the Graafian follicles. This causes the regeneration of the endometrium, follicular growth, and the growing follicles produce oestrogen.

• The LH and FSH are at their peak in the middle of the cycle (14^th day) and cause the rupture of the Graafian follicles to release ovum. This phase is called the ovulatory phase.

• In the absence of fertilisation, the corpus luteum degenerates, thereby causing the disintegration of the endometrium and the start of a new cycle.