NCERT Solution Class 12th Biology Chapter – 3 Human Reproduction Notes

NCERT Solution Class 12th Biology Chapter – 3 Human Reproduction

NCERT Solution Class 12th Biology Chapter – 3 Human Reproduction Notes Acrosome, Fertilization, Colostrum discuss Human Reproduction Notes

NCERT Solution Class 12th Biology Chapter – 3 Human Reproduction

Chapter – 3

Human Reproduction

Notes

Humans are sexually reproducing and viviparous. The reproductive events in humans induce the formation of gametes (gametogenesis) i.e.; sperms in. males and ovum in females, the transfer of sperms into the female genital tract (insemination), and the fusion of males and females garnets (fertilization) leading to the formation of zygote.

After the formation and development of the blastocyst and its attachment to the uterine wall (implantation), embryonic development (gestation), and delivery of the baby (parturition).

The male reproductive system is located in the pelvis region. It includes the pain of the testes along with accessory ducts, glands, and the external genitalia.

The female reproductive system consists of a pair of ovaries along with a pair of oviducts, uterus, cervix, vagina, and the external genitalia located in the pelvic region. The female reproductive also has a pair of memory glands that are integrated structurally and functionally to support the processes of ovulation, fertilization, pregnancy, birth, and child care.

The primary sex organs – the testis in the males and the ovaries in the females produce gametes i.e.; sperms and ovum, respectively, by the process called gametogenesis.

In testis, the immature male cells (spermatogonia) produce sperms by spermatogenesis that begins at puberty.

After the process of spermiogenesis, sperm heads become embedded in the Sertoli cells. There are finally released from the seminiferous tubules by the process called spermiation.

Sperm is composed of a head, neck, middle piece, and tail. A plasma membrane envelops the whole body of sperm.

The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis. Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary, no more oogonia are formed and added after birth.

The reproductive cycle in the female primates (e.g. monkeys, apes, and human beings) is called the menstrual cycle. The first menstruation begins at puberty and is called menarche. In human females, menstruation is repeated at an average interval of 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.

Rapid secretion of L, H leading to its maximum level during mid-cycle called LH surge induces rupture of Graafian follicle and thereby the release of an ovum (ovulation). The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian foil ice transform as the corpus luteum.

The corpus luteum secretes large amounts of progesterone which is essential for the maintenance of the endometrium. During pregnancy, all events of the menstrual cycle stop and therefore there is no menstruation.

In human beings, menstrual cycles cases around 50 years of age. This is termed menopause. Cyclic mensuration is an indicator of normal reproductive life between menarche to menopause.

Fertilization is the process of fusion of a sperm. During this process, 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. This ensures that only one sperm can fertilize an ovum.

The mitotic division starts as the zygote moves through the isthmus of the. oviduct towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called a morula.

The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide and cover the blastocyst. As a result, the blastocyte becomes embedded in the endometrium of the uterus. This is implantation and it leads to pregnancy.

The average duration of human pregnancy is about 9.5 months which is called the gestation period. Vigorous contraction of the uterus at the end of pregnancy causes expulsion/delivery of the fetus. The process of delivery of the fetus is called parturition.

The mammary glands of the female undergo differentiation during pregnancy and start producing milk towards the end of pregnancy by the process called lactation. The milk produced during the initial few days of lactation is called colostrum.

Leydig cells – Cells that synthesize and secrete testicular hormones called androgens.

Bulboureth rai glands – G Lands which help in the lubrication of the penis.

Clitoris – Tiny finger-like structure which lies at the upper junction of the two labia minora above the urethral opening.

Lactiferous duct – Duct through which milk is sucked out.

Spermiation – A process by which Sertoli cells are released from the seminiferous tubules.

Acrosome – Cap-like structure found ¡n sperm that help fertilization of the ovum.

Oogenesis – The process of formation of a mature female gamete.

Primary oocytes – The stage when cells start dividing and enter into prophase-l of the meiotic division and get temporarily arrested.

Menarche – The first menstruation begins at puberty and is called men arc he.

Menstrual cycle – In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next is called the menstrual cycle.

Menopause – Menstrual cycles cease around 50 years of age. that is termed menopause.

Fertilization – The process of fusion of a sperm with an ovum is called fertilization.

Implantation – When the blastocysts become embedded in the endometrium of the uterus, it is called implantation.

Relaxin – A hormone secreted by the ovary in the late part of pregnancy.

Parturition – The process of delivery of the fetus is called parturition.

Colostrum – The milk produced during the initial days of lactation is called colostrum.