CBSE Class 12 Biology Notes Chapter 3 Human Reproduction

Human reproduction is a form of sexual reproduction where new organisms are produced by the process of human fertilization. 

• The male reproductive system and the female reproductive system are two types of the human reproductive system.
• Reproduction is defined as the fundamental characteristics of living things where humans undergo internal fertilization by sexual intercourse.
• The process of transferring sperm to the female reproductive tract is called insemination.
• The fusion between male and female gametes will result in the formation of zygotes.
• Normal cell consists of 46 chromosomes, and the gamete consists of 23 single chromosomes.
• The female consists of a pair of ovaries, and the male consists of testicles.
• Human embryogenesis refers to the development of the zygote. 

According to the CBSE Syllabus 2023-24, the chapter on Human Reproduction Notes comes under Unit 1 of Reproduction. NCERT Class 12 Biology Unit Reproduction holds a weightage of around 16 marks.

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Class 12 Biology Chapter 3 Notes – Human Reproduction

Male Reproductive System

• The male reproductive system is located in the pelvis region of the human body.
• It consists of two parts, namely testicles and the penis.
• Sperms are formed in the male gametes.

Important parts of Male Reproductive System

• Scrotum: Scrotum, which is situated below the abdominal cavity, is used to maintain the temperature of testes.
• Testicular Lobes: Testicular lobules which are situated in the testes are used in the formation of male hormone testosterone.
• Sertoli Cells: Sertoli Cells are located at the lining of the tubules. 
• Interstitial Cells: Interstitial cells, also called Leydig cells, are used for the synthesis of testicular hormones called androgens.
• Accessory Ducts: Accessory Ducts are used for transporting and storing sperm through the urethra.
• Urethra Meatus: Urethra meatus is a type of external opening that originates from urinary bladder to penis.

Male Reproductive System

Female Reproductive System

• Female Reproductive System consists of oviducts, vagina, uterus, external genitalia and cervix. 
• The reproduction cycle of females consists of ovulation, fertilization, pregnancy, childbirth and child care.
• It helps in the formation of female sex hormones, which in turn help balance the reproductive cycle. 

Important parts of Female Reproductive System

• Ovaries: Ovaries are the main female sex organ which is used in the production of gamete and ovarian hormones.
• Accessory Ducts: Accessory ducts which are located near the ovary, consist of the vagina, fallopian tube and uterus.
• Fimbriae: Fimbriae that are placed by fallopian tubes are used for the ovum.
• Isthmus: Isthmus, also called womb, is connected to the uterus.
• Uterus: The uterus is a form of passage that is supported by the ligaments which are attached to the pelvic wall.
• Hymen: Hymen, which is torn at the time of coitus, is an indicator of virginity.

Female Reproductive System

Microscopic Anatomy of Testis

• Testis, also known as testicles, are found in the male reproductive system. 
• They are used for the generation of sperm, reproductive cells, and androgens.
• Testis are found behind the penis located at the scrotal sac.
• Each testis is enclosed in a capsule called tunica albuginea, which is divided into 200 to 400 wedge-shaped lobes.
• Seminiferous tubules found in the lobes help in the formation of sperms.
• Sertoli cells provide support to interstitial cells that result in the formation of testosterone. 

Testis

Microscopic Anatomy of Ovary

• Ovaries are used for the production of sex cells or ova in the female reproductive system.
• It is used for nourishment and preparation of eggs for ovulation.
• A female egg formed by reproduction is transferred to the uterus with the help of a fallopian tube.
• Female reproductive system consists of two ovaries which are 4 cm long, 2 cm broad, and 1.5 cm thick, and weigh 4 to 8 grams.
• They help in the shedding of the uterine lining during the menstrual cycle.

Gametogenesis

• Gametogenesis refers to the division of diploid cells to form new haploid cells.
• The primary sex organs of the male and female, namely sperm and ovum, will result in the formation of gamete.
• Spermatogenesis is a type of diploid cells that undergo mitotic division that is used for creation of sperms in the testes.
• GnRH, LH, FSH, and androgens help stimulate gametogenesis cells.
• The immature germ cells are converted into sperm at the time of puberty.
• Oogenesis is a process of converting oogonia into the mature ovum.
• Ovulation refers to the release of an ovum from the Graafian follicle.

Gametogenesis

Menstrual Cycle

• The menstrual cycle is a form of natural change in the production of female hormones.
• It is used for controlling the production and release of eggs along with the release of estrogen and progesterone.
• The shedding of the lining of the uterus when the ovum is not fertilized is called menstruation.
• The menstrual cycle is initiated from the age of 10 to 15 when a girl reaches puberty. 
• The ending of the menstruation cycle usually occurs at the age of 50, is called menopause.

Phases of Menstrual Cycle

• Menstrual phase: On day one, the lining of the uterus is prepared for implantation.
• Follicular phase: In this phase, the primary follicle is converted into a graffian follicle in order to start preparing it for another pregnancy.
• Ovulatory phase: This is the mid-cycle phase in which ovulation takes place.
• Luteal phase: This is the last phase where the fate of the corpus luteum is decided which means if fertilization takes place, then the woman will undergo pregnancy. 

Fertilization

• In fertilization, both egg and sperm are fused together, which results in the formation of a zygote.
• The process is carried out in the fallopian tube.
• In this, semen which is composed of thousands of sperms is inseminated into the female vagina at the time of coitus. 
• The sperm will be transferred to the fallopian tube after surviving the difficult environment in the cervix, vagina and uterus. 

Stages of Fertilization

• Acrosomal Reaction: The acrosomal reaction will help in the fusion of the plasma membrane of the secondary oocyte and the sperm 
• Cortical Reaction: Cortical reaction that is found under plasma membrane will result in the fusion of cortical granules and plasma membrane.
• Sperm Entry: It will result in the formation of a secondary oocyte, also known as the cone of reception.
• Karyogamy: Karyogamy will give rise to the formation of haploid ovum and a secondary polar body.

Fertilization

Blastocyst Formation

• Blastocyst, also known as blastocoel, refers to the process of formation of the trophectoderm and the fluid-filled cavity.
• The process of blastulation will be initiated after 5-14 days after fertilization.

Stages of Blastocyst Formation

• The zygote enclosed in the zona pellucida is divided into 2-celled, 4-celled, 8-celled, and 16-celled stages. 
• The 2-celled will result in the division of blastomeres into mitosis and cytokinesis. 
• The blastomers will form a junction, which is later converted into a mulberry-shaped cluster of cells called morula.
• This will result in the formation of an outer cell mass and an inner cell mass for the embryo.
• Later, this fluid is accumulated into a zygote for the formation of the blastocyst. 
• The blastocyst comprises two tissues: outer trophoblast and inner cell mass.
• The stretched pellucida breaks and releases the required blastocyst, which is called hatching. 
• The blastocyst is finally implanted inside the uterus.

Blastocyst Formation

Pregnancy and Placenta formation 

Pregnancy

• Pregnancy is a form of biological process where the female reproductive system will create one or more offspring.
• The pregnancy cycle will start on the first day of your last menstrual cycle.
• There are three stages of the trimester, where the first trimester involves pre-embryonic and embryonic development.
• The second stage of the trimester will include the formation of the fetus.
• This is the last stage, where the baby grows and matures.

Placenta

• The placenta helps in developing a connection between the mother and the developing embryo.
• It is initiated in the third week of pregnancy.
• The inner cell mass will help in the formation of the foetus.
• Similarly, trophoblast will help in the formation of the placenta.

Parturition 

• Parturition also known as labor which initiates the process of delivering a child after the completion of pregnancy period. 
• Along with cortisol, the cervix dilates and relaxes.
• In this process, the uterus of the woman will contract to push the fetus towards the cervix.
• The process of parturition continues until the fetus comes out of the mother's body

There are Some important List Of Top Biology Questions On Human Reproduction Asked In CBSE CLASS XII