BIOLOGY 3 Marks Question

Four reproductive events of sexual reproduction :
1. Gametogenesis
2. Gamete transfer
3. Fertilization
4. Embryogeny

self

Insemination : During copulation (coitus), semen is released by penis of man into vagina of women is called insemination.
Process of Fertilization : The motile sperms swim rapidly, pass through the cervix, enter into uterus and finally reach the ampullary region of the fallopian tube. Meanwhile ovum released by ovary during ovulation also reach the ampullary region where fertilization takes place. The process of fusion of a sperm with an ovum is called fertilization. During fertilization a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilize an ovum. The secretion of acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This induces the completion of the meiotic division of the secondary oocyte and it results into formation of second polar body and a haploid ovum. Soon the haploid nucleus of sperm and that of ovum fuse together forming diploid zygote.

Pregnancy : The process of attachment of the embryo as blastocyst in the endometrium of the uterus is called implantation and it leads to pregnancy. It is also indicated by stoppage of menstrual cycle.
Hormone maintaining the pregnancy are human chorionic genadotropin (hCG), human placental lactogen (hPL), estrogens, progestons. In the later phase of pregnancy, a hormone called relaxin is also secreted by the ovary. hCG, hPL and relaxin are produced in the women during pregnancy. In addition, during pregnancy the levels of other hormones like—estrogens, progestogens, cortisoles, prolactin, thyroxine etc. are increased several folds in maternal blood and increased level of these hormones is essential for supporting the foetal growth, metabolic changes in the mother and maintenance of pregnancy

Sertoli Cells : These cells are also called supporting or nurse cells. These cells are columnar shaped, elongated less in number and bigger in size. These cells have many spermatids to be clumped at their free end.
Functions :
1. These cells provide protection, support and nutrition to developing spermatids.
2. These cells degenerate the useless cytoplasm of spermatids.
3. These cells also secrete inhibin hormone to regulate the activities of FSH for spermatogenesis

1. Both spermatogenesis and oogenesis take place in gonads and begin by primary germ cells of germinal epithelicum.
2. Both the processes have three phases named multiplication phase, growth phase and maturation phase.
3. In multiplication phase, there occurs quantitative increase in germ cells by repeated mitotic division in both spermatogenesis and oogenesis.
4. Maturation phase involves two meiotic division both in spermatogenesis and oogenesis.

Various reproductive organs of human female and their important functions :

1. Ovary	Produces ova through oogenesis.
2. Oviducts	Fertilization occurs and also transfers the fertilized ovum or embryo in uterus.
3. Uterus	Implantation of embryo to endometrial wall of uterus and provides nutrition. The muscular contraction assists foetus to deliver during parturition.
4. Cervix	Produces watery mucus lubricate penis and sperms swim in it after ejaculation.
5. Vagina	Receives sperms through penis during coitus and acts as birth canal for delivery of baby during parturition.
6. Clitoris	Homologous to penis.

After ovulation, the follicle which ruptures is finally converted into a blood filled cavity called corpus haemorrhagicum. The follicle cells proliferate and the clotted blood is replaced by yellow lipid rich luteal cells thereby forming the corpus luteum. The formation and maintenance of corpus luteum is under the influence of LH. The corpus luteum is a temporary endocrine gland which secretes progestrone and relaxin.
If fertilization occurs, corpus luteum persists, but if not, it degenerates and is replaced by scar tissue called corpus albicans.
Functions :
1. Corpus luteum secretes progestrone which prepares the uterus for implantation of foetus to the womb’s wall and also maintains the pregnancy till birth.
2. It also secretes relaxin on completion of gestation period so that delivery of foetus can occur easily.

Man has three types of accessory glands. The secretion of these glands take part in semen formation :
(1) Prostate Glands : It is large lobulated, gland situated at the base of urethra. This gland secrets slightly white alkaline fluid which forms 25-30% of total semen and contains phosphates, citrates, lysozyme, fibrinolysin, spermin etc. It activates the sperms, provides nutrition and prevents coagulation of semen.
(2) Seminal Vesicle : These are one pair situated between the bladder and rectum. It is muscular and sacculated glands. These glands secrete alkaline fluid forming 60% of total semen. It contains prostaglandins and fructose. Fructose provides energy to sperms whereas prostaglandin stimulates vaginal contractions to help in fusion of gametes.
(3) Cowper Glands or Bulbourethral Gland : These glands secrete a viscous, sticky alkaline fluid during copulation which lubricates the penis and removes the acidity
of vaginal passage to protect the sperms. In this way we can conclude that secretum of accessory glands help in semen formation and reproductive process. 

Changes seen in male and female by onsetting of puberty :

In Males	In Females
1. Growth in size of penis, scrotal sacs, prostate and seminal vesicles.	1. Growth in size of uterus, vagina, oviduct and vulva.
2. Enlargement in testis size and beginning of spermatogenesis.	2. Enlargement of breast and beginning of menstrual cycle.
3. Growth of hair on face as beard and moustache and on chest.	3. Pubic and axillary hair grow
4. Voice becomes coarse.	4. The broading of hip region due to widening of pelvis.
5. Pubic and axillary hair grow.	5. Voice becomes thin, melodious.
6. Secretion of FSH, cowper gland, prostate gland and testosterone actively.	6. Secretion of FSH, estrogen, LH, oxytocin actively.
7. Psychological attraction towards female.	7. Psychological attraction towards male.

Oestrous Cycle : The cyclic changes occuring in the female reproductive tracts of non-primates mammal are known as oestrous cycle. During this cycle, female is in heat period and is ready for coitus.
Differences between Oestrous and Menstrual Cycle :

S.No.	Oestrous Cycle	Menstrual Cycle
1	It occurs in non-primates mammals.	It occurs in primates mammals.
2	Menstruation does not occur.	Menstruation occurs.
3	Endometrium is not de-generated but reabsorbed.	Endometrium is degenerated and goes out with menstrual.
4	Copulation only when female in oestrous or heat period.	It occurs at any time of year.

The human pregnancy lasts 9 months. The major features of embryonic development at various months of pregnancy are as follows :
1. In human being, after one month of pregnancy, the embryo heart is formed and heart sound can be carefully listened through the stethoscope.
2. By the end of 2nd month of pregnancy, the foetus develops limbs and digits.
3. By the end of 12 weeks/first trimester, most of the major organ systems are formed. For example : The limbs and external genital organs are well developed.
4. During the fifth month, the first movements of the foetus and appearance of hair on the head are usually observed.
5. By the end of 24 weeks, the body is covered with fine hair, eyelids separate and eyelashes are formed.
6. By the end of nine month of pregnancy, the foetus is fully developed and ready for delivery.