2nd PUC Biology Question and Answer: Human Reproduction
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Karnataka 2nd PUC Biology Textbook Answers—Reflections Chapter 3
Human Reproduction Questions and Answers, Notes, and Summary
2nd PUC Biology Chapter 3
Human Reproduction
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Question and Answer:
Question 1.
Fill in the blanks:
(a) Humans reproduce _____________ (asexually/sexually)
(b) Humans are _____________ (oviparous, viviparous, ovoviviparous)
(c) Fertilisation is _____________ in humans (external/internal) (d) Male and female gametes are _____________ (diploid/haploid)
(e) Zygote is _____________ (diploid/haploid)
(f) The process of release of ovum from a mature follicle is called _____________
(g) Ovulation is induced by a hormone called _____________ (h) The fusion of male and female gametes is called _____________
(i) Fertilisation takes place in _____________
(j) Zygote divides to form _____________which is implanted in uterus.
(k) The structure which provides vascular connection between foetus and uterus is called _____________
Answer:
(a) sexually.
(b) viviparous.
(c) internal
(d) haploid.
(e) diploid.
(f) ovulation.
(g) luteinizing hormone (LH).
(h) fertilisation.
(i) ampullary region of the fallopian tube.
(j) blastocyst.
(k) placenta.
Question 2.
Draw a labelled diagram of male reproductive system.
Answer:
Question 3.
Draw a labelled diagram of female reproductive system.
Answer:
Question 4.
Write two major functions each of testis and ovary.
Answer:
Testes:
Testes are the primary male reproductive organs. The two major functions of testes are:
- Production of testosterone from Leydig cells, which regulates male secondary sexual characters and reproductive functions.
- Production of sperm cells in the seminiferous tubules for reproduction.
Ovaries:
Ovaries are the primary female reproductive organs. The two major functions of ovaries are:
- Production of female germ cells called ova (eggs or oocytes).
- Secretion of hormones — estrogen and progesterone, which regulate the menstrual cycle, development of secondary sexual characters, and maintenance of pregnancy.
Question 5.
Describe the structure of a seminiferous tubule.
Answer:
Each testis has about 250 compartments (testicular lobules), and each lobule contains 1–3 highly coiled seminiferous tubules.
Each seminiferous tubule is lined by two types of cells:
- Male germ cells (spermatogonia): These are immature germ cells that undergo meiosis to form sperms.
- Sertoli cells: These provide nourishment and structural support to the developing germ cells.
The male germ cells and Sertoli cells together form the germinal epithelium.
Each seminiferous tubule is surrounded externally by a basement membrane, and between the tubules lie Leydig (interstitial) cells that secrete the male hormone testosterone.
Question 6.
What is spermatogenesis? Briefly describe the process of spermatogenesis.
Answer:
Definition:
Spermatogenesis is the process of production of haploid spermatozoa (n) from diploid spermatogonia (2n) inside the seminiferous tubules of the testis. It begins at puberty under the influence of hormones.
Hormonal Role in Spermatogenesis:
- The process begins with an increase in the secretion of GnRH (Gonadotropin-Releasing Hormone) from the hypothalamus.
- GnRH acts on the anterior pituitary gland, stimulating the release of two gonadotropins:
- LH (Luteinizing Hormone) or ICSH (Interstitial Cell Stimulating Hormone) – acts on Leydig cells to secrete testosterone and other androgens, which stimulate spermatogenesis.
- FSH (Follicle Stimulating Hormone) – acts on Sertoli cells, which secrete factors that help in spermiogenesis (the transformation of spermatids into spermatozoa).
- Sertoli cells also secrete inhibin, a hormone that suppresses FSH secretion to regulate the process.
Process of Spermatogenesis:
- Multiplication Phase:
- The spermatogonia (2n) divide by mitosis to form two types — Type A and Type B spermatogonia.
- Type A acts as mother spermatogonia to maintain the germ cell line.
- Type B grows in size and differentiates into primary spermatocytes.
- Growth and Maturation Phase:
- Each primary spermatocyte (2n) undergoes first meiotic division to form two secondary spermatocytes (n).
- Each secondary spermatocyte undergoes second meiotic division to form four haploid spermatids (n).
- Spermiogenesis:
- The spermatids are gradually transformed into mature, motile spermatozoa (sperms).
- The Sertoli cells provide nutrition and support during this process.
- Spermiation:
- After spermiogenesis, the sperm heads become embedded in Sertoli cells and are finally released into the lumen of seminiferous tubules — this release is called spermiation.
Summary:
Spermatogenesis ensures the continuous production of male gametes throughout adult life, controlled by coordinated hormonal regulation involving GnRH, LH, FSH, testosterone, and inhibin.
Question 7.
Name the hormones involved in regulation of spermatogenesis.
Answer:
After sexual maturity, spermatogenesis begins due to the secretion of Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus of the brain.
GnRH acts on the anterior pituitary gland and stimulates the secretion of two gonadotropins:
- Luteinizing Hormone (LH):
LH acts on the Leydig’s cells of the testis to produce male sex hormones (androgens) such as testosterone. High levels of androgens stimulate the process of spermatogenesis. - Follicle Stimulating Hormone (FSH):
FSH acts on the Sertoli cells and stimulates the secretion of certain factors that help in the process of spermiogenesis (transformation of spermatids into spermatozoa).
Question 8.
Define spermiogenesis and spermiation.
Answer:
- Spermiogenesis:
It is the final stage of spermatogenesis in which spermatids mature into motile and functional spermatozoa (sperms). - Spermiation:
It is the process of release of mature spermatozoa from the surface of Sertoli cells into the lumen of the seminiferous tubules.
Question 9.
Draw a labelled diagram of sperm.
Answer:
Question 10.
What are the major components of seminal plasma?
Answer:
Seminal plasma consists of secretions from the seminal vesicles, prostate gland, and bulbourethral glands.
- Seminal vesicles: Secrete fructose, prostaglandins, citrate, inositol, and clotting proteins.
- Prostate gland: Secretes calcium, phosphate, bicarbonate, enzymes, and prostaglandins.
- Bulbourethral glands: Secrete mucus for lubrication.
Summary:
Seminal plasma is a nutrient-rich fluid that provides energy, protection, and a suitable medium for the movement and survival of sperms.
Question 11.
What are the major functions of male accessory ducts and glands?
Answer:
Functions of male accessory ducts:
- Help in transport of sperms.
- Provide temporary storage for sperms.
Functions of male accessory glands:
- Their secretions form the seminal plasma.
- Seminal plasma contains fructose, enzymes, calcium, and prostaglandins.
- These secretions nourish the sperms and help them move actively.
Question 12.
What is oogenesis? Give a brief account of oogenesis.
Answer:
Oogenesis is the process of formation, development, and maturation of a haploid ovum (female gamete) from a diploid germ cell in the ovary.
Steps of Oogenesis:
- Oogonia formation:
- The cells of the germinal epithelium of the ovary divide repeatedly by mitosis to form diploid oogonia (egg mother cells).
- These are formed in large numbers in the fetal ovary.
- Primary oocyte formation:
- Oogonia grow in size and become primary oocytes.
- Each primary oocyte is surrounded by follicle cells and remains inactive until puberty.
- Formation of secondary oocyte and polar body:
- The primary oocyte undergoes its first meiotic division, which is unequal.
- This forms one large haploid secondary oocyte and one small first polar body.
- Ovulation and completion of meiosis:
- The secondary oocyte begins the second meiotic division, but it stops at metaphase.
- Ovulation occurs at this stage, and the oocyte is released into the fallopian tube.
- The second meiotic division completes only if fertilization occurs, forming a mature ovum and a second polar body.
Question 13.
Draw a labelled diagram of a section through ovary.
Answer:
Question 14.
Draw a labelled diagram of a Graafian follicle?
Answer:
Question 15.
Name the functions of the following:
(a) Corpus luteum
(b) Endometrium
(c) Acrosome
(d) Sperm tail
(e) Fimbriae
(a) Corpus luteum:
→ Secretes the hormone progesterone, which maintains the endometrium of the uterus for implantation and pregnancy.
(b) Endometrium:
→ The inner lining of the uterus where the fertilized egg implants and develops.
→ It sheds off during menstruation if fertilization does not occur.
(c) Acrosome:
→ A cap-like structure on the head of the sperm containing enzymes that help the sperm penetrate the egg membrane during fertilization.
(d) Sperm tail:
→ Helps in movement (motility) of the sperm, allowing it to swim toward the ovum for fertilization.
(e) Fimbriae:
→ Finger-like projections at the end of the fallopian tubes that collect the ovum released from the ovary and guide it into the tube.
Question 16.
Identify True/False statements. Correct each false statement to make it true.
(a) Androgens are produced by Sertoli cells. (True/False)
(b) Spermatozoa get nutrition from Sertoli cells. (True/False)
(c) Leydig cells are found in ovary. (True/False)
(d) Leydig cells synthesise androgens. (True/False)
(e) Oogenesis takes place in corpus luteum. (True/False)
(f) Menstrual cycle ceases during pregnancy. (True/False)
(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience. (True/False)
Answer:
- Androgens are produced by Leydig cells.
- True
- It is found in the testis.
- True
- Oogenesis takes place in the ovary.
- True
- True
Question 17.
What is menstrual cycle? Which hormones regulate menstrual cycle?
Answer:
The menstrual cycle is the reproductive cycle in female primates (like humans).
During this cycle, the lining of the uterus (endometrium) becomes thick and spongy to receive a fertilized egg.
If the egg is not fertilized, this lining is shed off through the vagina along with blood and mucus — this process is called menstruation.
The menstrual cycle repeats every 28 to 29 days on average.
Hormones that regulate the menstrual cycle:
- Gonadotropin (GnRH):
Stimulates the pituitary gland to secrete FSH and LH. - Follicle Stimulating Hormone (FSH):
Helps in the growth and development of ovarian follicles. - Luteinizing Hormone (LH):
Triggers ovulation and formation of the corpus luteum. - Estrogen:
Helps in the repair and thickening of the uterine lining (endometrium). - Progesterone:
Maintains the endometrium for implantation and supports pregnancy.
Question 18.
What is parturition? Which hormones are involved in induction of parturition?
Answer:
The average duration of human pregnancy is about 9 months, called the gestation period.
At the end of this period, vigorous contractions of the uterus cause the delivery (expulsion) of the foetus, and this process is called parturition (childbirth).
Parturition is mainly induced by the hormone oxytocin, which acts on the uterine muscles to cause strong contractions.
These contractions further stimulate the release of more oxytocin — forming a positive feedback loop until the baby is delivered.
Other hormones involved:
- Relaxin: Helps to relax pelvic ligaments and soften the cervix for easy childbirth.
- Prostaglandins: Enhance uterine contractions during labour.
Question 19.
In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?
Answer:
Sex chromosome pattern in females is xx, i.e., both the gametes are with ‘X’ chromosomes. In males, sex chromosome is X Y i.e., one gamete with ‘X’ chromosome and other gametes with ‘Y’. So 50% sperms carry ‘X’ and 50% carry ‘Y’. A female child is producing when the sperm with ‘X’ chromosome fertilizes egg with ‘X’ chromosome. A male child is producing when sperm with ‘Y’ chromosome fertilizes egg with ‘X’ chromosome. Therefore sex of a baby depends on the father, not on the mother.
Question 20.
- How many eggs are released by a human ovary in a month?
- How many eggs do you think would have been released if the mother gave birth to identical twins?
- Would your answer change if the twins born were fraternal?
Answer:
(a) Only one egg is released by a human (female) ovary in a month.
(b) Only one egg is released if the mother gave birth to identical twins, as they develop from a single fertilized egg that splits into two embryos.
(c) Yes, two or more eggs are released in case fraternal twins are born, as they develop from two different eggs fertilized by two different sperms.
Question 21.
How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?
Answer:
In dogs, each puppy develops from a separate egg fertilized by a separate sperm.
So, the ovary of the female dog must have released six eggs, one for each puppy.
Additional Questions and Answers
Question 1.
What is the function of the scrotum?
Answer:
The scrotum helps to maintain the testes at a temperature lower than the body temperature, which is necessary for the formation of sperms.
Question 2.
What is the role of the placenta during pregnancy?
Answer:
The placenta provides nutrients and oxygen to the developing embryo and removes waste products from its blood.
Question 3.
What is the function of the amniotic fluid?
Answer:
Amniotic fluid protects the developing embryo from mechanical shocks and helps maintain a constant temperature.
Question 4.
Name the events of fertilization.
Answer:
The main events of fertilization are:
- Sperm penetration into the ovum.
- Fusion of male and female nuclei.
- Formation of zygote.
Question 5.
What is implantation?
Answer:
Implantation is the process by which the blastocyst attaches to the wall of the uterus for further development.
Question 6.
What is colostrum?
Answer:
Colostrum is the first milk produced after childbirth, rich in proteins and antibodies that provide immunity to the newborn.
Question 7.
What is spermatogenesis?
Answer:
Spermatogenesis is the process of formation of sperms from spermatogonial cells in the testes.
Question 8.
What is ovulation?
Answer:
Ovulation is the release of a mature ovum (egg) from the ovary into the fallopian tube, usually around the 14th day of the menstrual cycle.
Question 9.
What is lactation?
Answer:
Lactation is the process of secretion of milk from the mammary glands after childbirth.
Question 10.
What is the function of oxytocin in females?
Answer:
Oxytocin stimulates uterine contractions during childbirth and helps in the ejection of milk during breastfeeding.