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| Name of Board | AHSEC |
| Class: | Assam Board Class 12 |
| Subject: | AHSEC Class 12 Biology |
| Number of Chapter: | 02 |
| Chapter Name | Human Reproduction |
| Content Type: | Text, Images, and PDF Format |
| Academic Year: | 2024-25 |
| Medium: | English |
| Available Solution Link: | AHSEC Class Biology Notes |
AHSEC Class 12th Biology Chapter: 2 Human Reproduction
(A) FILL IN THE BLANKS (ONE MARK EACH)
1. The process of formation of gametes is called______.
Ans: Gametogenesis
2. The testes in mammals are situated outside the abdominal cavity within a pouch called______.
Ans: Scrotum
3. The process of release of ovum from the mature follicle is called_______.
Ans: Ovulation
4. Ovulation is induced by a hormone called______.
Ans: Luteinising hormone
5. The fusion of a male and female gamete is called-
Ans: Fertilisation
6. Secondary spermatocytes are formed from_______by first meiotic division.
Ans: Primary spermatocytes /Spermatogonia
7. Zygote divides to form_____” -which is implanted in uterus.
Ans: Blastocyst
8. The structure which provides the connection between foetus and the uterus of the mother is called_______.
Ans: Placenta
9. Degenerated corpus luteum is called_______.
Ans: Corpus albicans.
10. The process which transform the zygote to a blastula is called________.
Ans: Cleavage
11. The gestation period of a human female is_______.
Ans: 9 months
12. Cessation of the menstrual cycle in a female is called________.
Ans: Menopause
13. Progesterone is secreted by_______.
Ans: Corpus luteum
14. The secretory phase of the menstruation cycle is also called the_________.
Ans: Luteal phase
15. Each ovary is connected to the pelvic wall and uterus wall by_______.
Ans: Ligaments
16. The acrosome of sperm is formed from the______.
Ans: Golgi complex of spermatid.
[B] TRUE OR FALSE (ONE MARKS EACH)
1. Humans are ovoviviparous.
Ans: False
2. Leydig cells are present in the interstitial spaces between the seminiferous tubules.
Ans: True
3. The funnel-shaped part of the fallopian tube close to the ovary is called isthmus.
Ans: False
4. The secondary spermatocytes contain haploid chromosomes.
Ans: True
5. Spermatogonia undergo mitotic division.
Ans: True
6. GnRH is an anterior pituitary hormone.
Ans: False
7. The primary ovarian follicle is also called Graffian follicle.
Ans: False
8. XY sex chromosomes are found in human male.
Ans. True
9. Blastocyst is formed from the morula.
Ans.: True
10. Acrosome is found in female gamete.
Ans.: False
[C] VERY SHORT ANSWER QUESTIONS
(1 Mark each)
1. State the difference in reproductive age of man and woman.
Ans: In male sperm formation continues even in old age but formation of the ovum ceases in women around the age of fifty years.
2. What is urethral meatus?
Ans: Urethral meatus is the external opening of the urethra.
3. Name 2 male accessory glands.
Ans: Prostrate gland and Bulbourethral gland.
4. State the components of seminal plasma.
Ans: Seminal plasma is rich in fructose calcium and certain enzymes.
5. Define spermiation.
Ans: Spermiation is the process of release of the spermatozoa from the seminiferous tubules.
6. What is the function of acrosome?
Ans: The acrosome contains hydrolytic enzymes that help in dissolving membranes of the ovum for fertilisation.
7. Why sperm contains mitochondria?
Ans: Mitochondria produces energy for the movement of tail that facilitate sperm motility essential for fertilisation.
8. Name the hormones which maintain the function of the male sex accessory ducts and glands.
Ans: Testicular hormones (androgens).
9. What is semen?
Ans: The seminal plasma along with the sperms constitute the semen.
10. Why human female has fixed number of primary follicle in the ovary?
Ans: Because a large number of primary follicles degenerate during the phase from birth to puberty.
11. What do you understand by ovulation?
Ans: Ovulation is the process of rupture of a mature graafian follicle and release of the ovum (secondary oocyte) from it.
12. Define menstrual cycle.
Ans: The reproductive cycle in female primates is called menstrual cycle.
13. How the corpus luteum is formed?
Ans: After ovulation, the remaining part of the graafian follicle passes through the luteal phase and get transformed into corpus luteum.
14. What happens to corpus luteum in the absence of fertilization?
Ans: In the absence of fertilization, the corpus luteum degenerates which cause the disintegration of the endometrium leading to menstruation.
15. Define menopause.
Ans: Menopause is the cessation of menstruation around 50 years of age.
16. Name the secretion of corpus luteum.
Ans: The corpus luteum secretes large amounts of progesterone.
17. What is fertilisation?
Ans: The process of fusion of a sperm with an ovum is called fertilisation.
18. You studied the chromosome of a human and found that there present two identical sex chromosomes what will be the sex of the individual.
Ans: Female
19. How many sex chromosome is present in the sperm?
Ans: 23.
20. What are the two layers of cells found in the blastocyst?
Ans: Outer layer called trophoblast and an inner group of cells attached to the trophoblast called inner cell mass.
21. Name an organ which is found of tissues of two different individuals.
Ans: Placenta.
[D] SHORT ANSWER QUESTIONS (2 MARKS EACH)
1. What is the significance of presence of testes within scroteum?
Ans: In the scrotum the temperature remains 2-2.5°c lower than the internal body temperature which is essential for the formation of sperms.
2. Write the functions of two types of cells found within the seminiferous tubule.
Ans: The two types of cells found within the seminiferous tubule are
(i) Male germ cells (spermatogonia) which undergo meiotic divisions leading to sperm formation.
(ii) Sertoli cells provide nutrition to the germ cells..
3. Name the different events of reproduction occur in human.
Ans: The reproductive events are
(i) Formation of gametes (gametogenesis)
(ii) Transfer of sperms into the female genital tract (insemination)
(iii) Fusion of male and female gamete (fertilisation) leading to formation of zygote.
(iv) Formation and development of blastocyst and its attachment to the uterine wall (implantation)
(v) embryonic development (gestation)
(vi) Delivery of the baby (parturition)
4. What is leydig cell? State its function.
Ans: The regions outside the seminiferous tubules contain masses of cells called leydig cells. Its function is to synthesise and secrete testicular hormones called androgens which maintain male sex characteristics.
5. State the function of FSH and LH.
Ans: LH acts at the leydig cells and stimulates synthesis and secretion of androgens.
FSH acts on the sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.
6. State the structure of sperm head.
Ans: Sperm head is the enlarged end of a sperm, containing an elongated haploid nucleus, the interior portion of which is covered by a cap like structure called acrosome. The acrosome is filled with enzymes that help in fertilisation of the ovum.
7. Why unequal division of cytoplasm occurs during formation of ovum?
Ans: Unequal division of cytoplasm occur to form a large secondary oocyte and a small polar body. The secondary oocyte retains bulk of the nutrient rich cytoplasm of the primary oocyte which further changes into the mature Graffian follicle. The polar body does not divide further.
8. What are the changes that occurred during follicular phase of menstrual cycle in human female?
Ans: During this phase, the primary follicles in the ovary grow to become a fully mature graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and uterus are induced by changes in the levels of pituitary and ovarian hormones. The secretion of LH and FSH increases gradually during the follicular phase and stimulates follicular development as well as secretion of estrogens by the growing follicles.
9. Differentiate between menarche and menopause.
Ans: Menarche is the beginning of menstruation at puberty in primate females.
Menopause is the cessation of menstruation and the menstrual cycle in primate females at around the age of 50.
10. State the functions of progesterone.
Ans: (i) Prepares the uterus for implantation of the blastocyst to the uterine wall.
(ii) helps in the formation of placent
(iii) Maintain endometrium.
11. How implantation of a human embryo occur in the mother’s uterus?
Ans: Zygote divides rapidly by mitosis and produces 2,4,8,16 daughter cells called blastomeres. An embryo with 8-16 blastomere is called morula which further divides to form a blastocyst. Blastocyst have an outer layer of trophoblast and inner layer of cell mass. The trophoblast gets attached to the endometrium and the inner cell mass gets differentiated into an embryo. As a result, the blastocyst becomes embedded in the endometrium of the uterus called implantation.
12. State the functions of placenta
Ans: The functions of placenta are
(1) Provides nutrients and oxygen to the developing embryo.
(ii) Removes co₂ and waste materials from the embryo.
(iii) Produces several hormones like hCG, hPL, estrogen, progestogen etc that are essential to maintain pregnancy.
13. How placenta is formed?
Ans: After implantation, finger like projections appear on the trophoblast called chorionic villi which are surrounded by the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta.
14. What are stem cells? Where they are found?
Ans: Stem cells are the cells that have the potency to give rise to all the tissues and organs. They are found in the inner cell mass.
15. Why breast feeding during initial period of infant growth is recommended?
Ans: The milk produced during the initial few days of lactation is called colostrum which contains several antibodies essential to develop resistance for the new born babies. Thus breast feeding during initial period of infant growth is recommended.
17. Describe the luteal phase of the menstrual cycle.
Ans. In the luteal phase the ruptured follicle changes into corpus luteum in the ovary and it begins to secrete progesterone hormone. The endometrium thickens further and their glands secrete a fluid unto the uterus. If ovum is not fertilized the corpus luteum undergoes degeneration and this courses disintegration of the endometrium leading to menstruation. Estrogen and progesterone levels rise during this phase. It last for only 1 day.
[E] SHORT ANSWER QUESTION (3 MARKS EACH)
1. Describe the male accessory duct system of human.
Ans: The male accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens.
(i) The seminiferous tubules of the testes open into the vasa efferentia through rete testis.
(ii) The vasa efferentia leave the testis and open into epididymis located along the posterior surface of each testis.
(iii) The epididymis leads to vas deferens that ascends to the abdomen and loops over the urinary bladder. The epididymis temporarily stores immature sperms.
(iv) The duct from seminal vesicle and vas deferens together from the ejaculatory duct. These ducts store and transport the sperms from the testis to the outside through urethra.
2. Draw and label the internal structure of the seminiferous tubules.
3. Draw and label the sectional view of the female reproductive system.
Ans:-
4. Write a note on the layers of tissues of the wall of the uterus.
Ans: The wall of the uterus has three layers of tissue
(i) Perimetrium outer thin covering of the uterus wall.
(ii) Myometrium middle thick layer of smooth muscle fibres which contract strongly during delivery of the baby.
(iii) Endometrium inner layer that contains glands and many blood vessels. It undergoes cyclical changes during the menstrual cycle.
5. Draw a neat labelled diagram of a human sperm.
Ans:
6. Distinguish between spermatogenesis & oogenesis.
Ans:-
| Spermatogenesis | Oogenesis |
| The production of sperms from spermatogonia is known as spermatogenesis | The production of eggs from oogonia is known as oogenesis |
| Occurs in testes | Occurs inside the ovary |
| All stages are completed in testes | The major part of oogenesis occurs inside the ovary. The last few stages occur in the oviduct. |
| It is a continuous process | It is a discontinuous process. The early stages take place in the foetus and the rest in later stages of life. |
| Equal cytokinesis occurs during the spermatogenesis producing four sperms | Unequal cytokinesis occurs during oogenesis ultimately producing one large ovum and tiny polar bodies |
7. Diagrammatically represents the various events of menstrual cycle.
Ans:-
:
8. Discuss the events of fertilisation in man.
Ans: (i) The process of fusion of a sperm with an ovum is called fertilisation.
(ii) During coitus semen is released by the penis into the vagina (insemination).
(iii) The motile sperms swim rapidly through the cervix, enter into the uterus and reach the ampullary isthmic junction of the oviduct.
(iv) A sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane to block the entry of additional sperms.
(v) The enzymes of the acrosome of sperm help to dissolve zona pellucida and plasma membrane of the arum and sperm head is allowed to enter into the cytoplasm of the ovum.
(vi) Ultimately diploid zygote is formed by the fusion of sperm and ovum.
9. State how sex of human is determined
Ans: Sex chromosome pattern in females is xx i.e. all gametes have x chromosomes. while in males is xy i.e. some gametes have x and some have y chromosomes. At the time of fertilisation when x chromosome of male combines with x chromosome of female, xx zygote is formed which would be a female. When y chromosome of male combines with x chromosome of female, xy zygote is formed which would be a male. Thus sex of human is determined by the father not by the mother.
10. Describe briefly the embryonic development up to blastocyst stage.
Ans: The embryonic development upto blastocyst stage consists of the following stages –
1. Cleavage The zygote undergoes successive mitotic divisions called cleavage, as it moves through the isthmus of fallopian tube towards the uterus. The daughter cells are called blastomeres.
2. Morula At the 16 celled stage the embryo is a solid sphere and is called a morula
3. Blastocyst Cell divisions continue in the morula and the blastomeres become arranged along the periphery leaving a central cavity called blastocoel, the embryo at this stage is called blastocyst. The cells now become arranged as an outer layer called trophoblast and an inner group of cells called inner cell ma attached to trophoblast and projecting into the blastocoel.
11. What is parturition? Discuss the process of parturition in human.
Ans: Parturition is the process of expulsion of the foetus from the mother’s uterus at the end of pregnancy.
Parturition is induced by a complex neuroendocrine mechanism The signals for parturition originate from the fully developed foetus and the placenta which induce meld uterine controctions called foetal ejection reflex. This triggers release of oxytocin from the maternal pituitary. Oxytocin acts on the uterine muscles and causes stronger uterine contactions. The stimulatory reflex between the uterine contraction and oxytocin secretion leads to expulsion of the baby out of the uterus through the birth canal.
12. “Placenta acts as an endocrine tissue.” Justify
Ans: Placenta produces several hormones like human chorionic ganadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens etc. These hormones are essential for supporting the foetal growth, metabolic changes in the mother and maintenance of pregnancy.
13. Discuss the role of hormones in menstrual cycle.
Ans. The secretion of Follicle stimulating hormone (FSH) and Luteinising hormone (LH) increases gradually during the follicular phase and stimulates follicular development as well as secretion of estrogens by the growing follicles. Both LH and FSH attain a peak level in the middle of cycle. Rapid secretion of LH induces rupture of graafian follicle and release of ovum, During luteal phase the remaining parts of the graafian follicle transfer as carpus luteum that secretes are amounts of progesterone that is essential for the maintenance of endo metrium. Such an endometrium is necessary for implantation of the fertilized ovum and other events of pregnancy.
[F] LONG ANSWER QUESTION (5 MARKS)
1. Describe the structure of testis with neat labelled diagram
Ans: The testis are located outside the abdominal cavity within a pouch called scrotum that provides a temperature 2-2.5°C lower than the body temperature necessary for spermatogenesis. Each testis is oval in shape and measures about 5cm in length 2-3 cm in width and about 3cm in thickness. The testis is covered by a dense covering called tunica albuginea. Internally the testis is divided into about 250 compartments, called testicular lobules. Each lobule contains 1-3 highly coiled seminiferous tubules in which sperms are produced.
Each seminiferous tubule lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells. The spermatogonia undergo meiotic divisions leading to sperm formation and sertoli cells provide nutrition to the germ cells. The regions outside the seminiferous tubules called interstitial spaces, contain small blood vessels and interstitial cells or Leydig cells, which synthesise and secrete androgens. The seminiferous tubules
(Diagrammatic viw of male reproductive system (part of testis is open to show inner details)
opens into vasa efferentia through rete testis. The vasa efferentia leave the testis and open into epididymis losated along the poste rior surface of each testis. 1
2. Describe the female reproductive system in human.
Ans: Human female reproductive system consists of the following
(i) A pair of ovaries: Ovaries are primary female sex organs that produce the female gamete and several steroid hormones. The ovaries are located one on each side of the lower abdomen. Each ovary is about 2 to 4 cm in length and is connected to the pelvic wall and uterus by ligaments. They are covered by a thin epithelium which encloses the ovarian stroma.
(ii) Accessory ducts: It includes oviducts fallopian tubes), uterus, vagina.
(a) Fallopian tube Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus. The part closer to the ovary is infundibulum, the edges of which possess finger like projections called finbriae. The infundibulum leads to a wider part called ampulla and the last part of the oviduct is called isthmus.
(b) Uterus: It is a single, muscular, inverted pear shaped structure supported by ligaments and attached to the pelvic wall. The lower part of uterus is very narrow and is called cervix. The uterus wall has 3 layers of tissue-external perimetrium, middle myometrium and inner endometrium.
(c) Vagina: It is a muscular tube like structure that opens to the outside. The cervix and the vagina together constitute the birth canal.
(iii) External genitalia: It includes mons pubis labia majora, labia minora, hymen and clitoris. Mons pubis is a cushion of fatty tissue covered by skin and pubic hair. Labia majora are fleshy folds of tissue that surround the vaginal opening. Labia minora are paired folds of tissue under the labia mayora. The opening of the vagina is covered partially by a membrane called hymen and clitoris is a tiny finger like structure which lies at the upper junction of the two labia minora above the urethral opening.
(iv) Mammary glands are paired structures that contain glandular tissue and variable amount of fat.
3. Give the structure of the mammary gland with neat diagram.
Ans: The mammary glands are paired structures that contain glandular tissue and variable amount of fat. The glandular tissue of each breast is divided into 15-20 mammary lobes containing clusters of cells called alveoli. The cells of alveoli secrete milk, which is stored in the cavities (lumens) of alveoli. The alveoli open into mammary tubules. The tubules of each lobe join to form a mammary duct. Several mammary ducts join to form a wider mammary ampulla which is connected to lactiferous duct through which milk is sucked out.
(Diagrammatic Sectional viw of Mammary gland)
4. Explain the process of spermatogenesis.
Ans: The process of formation of spermatozoa (sperms) from diploid spermatogonia is called spermatogenesis. It includes the following phases –
(a) Multiplication phase: The spermatogonia present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers.
(b) Growth phase: Spermatogonia grow and increase in size and forms primary spermatocytes. Each spermatogonia is diploid and contain 46 chromosomes.
(c) Maturation phase: Some of the spermatogonia called primary spermatocytes periodically undergo meiosis. A primary spermatocyte completes the first meiotic division leading to formation of two equal haploid cells called secondary spermatocytes which have only 23 chromosomes. The secondary spermatocytes undergo the second meiotic division to produce four equal haploid spermatids.
(d) Defferentiation phase: The spermatids are transformed into spermatozoa (sperms) by the process of spermeogenesis. After spermiogenesis sperm heads become embedded in the sertoli cells and are finally released from the seminiferous tubules by the process called spermiation.
5. Describe the role of hormones in initiating spermatogenesis at puberty.
Ans: Spermatogenesis starts at the age of puberty due to significant increase in the secretion of gonadotropin releasing hormone (GnRH) which is a hypothalamic hormone. The increased levels of GnRH then acts at the anterior pituitary gland and stimulates secretion of two gonadotropins luteinising hormone (LH) and follicle stimulating hormone (FSH). LH acts at the Laydig cells and stimulates synthesis and secretion of androgens. Androgens, stimulate the process of spermatogenesis. FSH acts n the sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.
6. Describe the process of development of human embryo since one month of pregnancy.
Ans: (i) After one month of pregnancy the heart is formed; the first sign of growing foetus is the heart beat.
(ii) By the end of the second month the foetus develops limbs and digits.
(iii) By the end of third month (first trimester) most of the organ systems are formed for eg, the limbs and external genital organs are well developed.
(iv) During the fifth month hair appears on the head and the foetus also shows slow movements.
(v) By the end of 24 weeks (second trimester the body is covered with fine hair, ayelids separate and eyelashes are also formed.
(vi) By the end of the nine months of pregnancy, the foetus is completely developed and is ready for its delivery.
7. Discuss the process of fertilization in human.
Ans. The process of fusion of a sperm with an ovum is called fertilisation. During coitus semen is released by the penis into the vagina (insemination). The motile sperms swim rapidly through the cervix, enter into the uterus and reach the ampullary- isthmic junction of the oviduct. The ovum released by the ovary us also transported to the ampullary isthmic junction where fertilisation takes place.
A sperm comes in contact with the zone pellucida layer of the ovum and induces changes in the membrane. to black the entry of additional sperm. The enzymes of the acrosome of sperm help to dissolve zona pellucida and plasma membrane of the ovum and sperm head is allowed to enter into the ectoplasm of the ovum.
Ultimately diploid zygote is produced by the fusion of a sperm and an ovum.
8. Describe pregnancy and embryonic development in human.
Ans. The cells of the trophoblast differentiate into an inner layer and an outer layer. The outer layer is called the chorion and forms the chorionic villi which are finger like projections that fro into the endometrium. An intimate connection is established between the chorionic villi and citrine tissues and forms a structural and functional unit between the developing embryo and the mothers body called placenta. The placenta provides nutrients and oxygen to the developing embryo and also removes co, and waste materials from the embryo. It also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progestogens that are essential to maintain pertinency.
Immediately after implantation the inner cell mass differentiates into an outer layer called ectoderm middle layer called mesodum and an inner layer called endoderm. These three layers gives rise to all tissues (organs) in adults. In human beings after one month of pregnancy the embryos heart is formed. By the end of the second month, the foetus develops limbs and digits. By the end of 12 weeks most of the major orgon systems are formed. The first movement of the foetus and appearance of hair on the head are usually observed during the fifth month. By the end of 24 weeks, the body is covered with fine hair, eye lids separate and eyelashes are formed. By the end of nine months of pregnancy, the foetus is fully developed and is ready for delivery.
SPECIAL ONE MARK QUESTIONS.
1. The process by which spermatids are transformed into spermatozoa.
Ans: Spermiogenesis
2. The fluid filled cavity of the ovarian follicle.
Ans: Antrum
3. The membrane surrounds the secondary oocyte.
Ans: Theca
4. The first mensuration which begins at puberty.
Ans: Menarche
5. The daughter cells formed by cleavage.
Ans: Blastomeres
6. The milk produced during initial few days of lactation.
Ans: Colostrum.
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