CBSE Important Questions Class 12 Biology Chapter 3

Important Questions Class 12 Biology Chapter 3

Important Questions for CBSE Class 12 Biology Chapter 3 – Human Reproduction

Students can access a  set of Important Questions Class 12 Biology Chapter 3 from the Extramarks website. These questions include the marks distribution, terminologies, and concepts related to Human Reproduction. Chapter 3 Class 12 Biology Important Questions prepared by Extramarks subject matter experts will provide accurate points for students to include in their answers.

Class 12 Biology Chapter 3 Important Questions are presented with step-by-step explanations. Concise answers are provided and created in accordance with the latest CBSE syllabus. 

CBSE Class 12 Biology Chapter-3 Important Questions

Study Important Questions Class 12 Biology Chapter 3- Human Reproduction

1 Mark Questions and Answers

Q1. What is parturition?

Ans: Parturition is the intense contraction of the uterus that leads to the delivery of the child at the end of nine months of pregnancy.

Q2. Despite the presence of several sperms in the vicinity of an egg cell, only one sperm enters the ovum. Explain?

Ans: Even though several sperms are there in the surroundings of an egg cell only one sperm enters the ovum because when sperm has an encounter with the ovum (zona pellucida) it instigates changes in the membrane to block the entry of the remaining sperms.

Q3. What is the function of Leydig cells?

Ans: The Leydig cells synthesise and release testicular hormones known as androgens.

Q4. State the reason why the male testes are located outside the abdominal cavity.

Ans: Male testes are located outside the abdominal cavity called the scrotum because it provides a lower temperature than the typical body temperature i.e(2-3℃) needed for spermatogenesis.

Q5. How is polyspermy checked by the zona pellucida of the ovum?

Ans. The zona pellucida of the ovum is a thick layer that is surrounded by corona radiata cells. The cortical granules are discharged from the egg which blocks the fusion of several sperms with an egg during the process of fertilisation.

Q6. What is the importance of the cervix in the female reproductive system?

Ans. The cervix is an important part of the female reproductive system as it is a narrow opening through which the uterus opens up to the vagina. The cervical canal is the cavity of the cervix which alongside the vagina connects to the birth canal.

Q7. Explain the function of the epididymis in male fertility.

Ans. It is situated along the posterior surface of each testis where spermatozoa obtain motility and the capability to fertilise the egg. The surface of the sperm is changed in response to discharges of the epididymis, which is necessary for fertilisation of an egg.

Q8. State the role of the ampullary-isthmic junction in the female reproductive tract.

Ans. Fertilisation of the ovum happens in the ampullary-isthmic junction which is an important process of reproduction.

2 Marks Questions and Answers

Q1. Give a reason for the following statements :

• The first half of the menstrual cycle is called the follicular phase as well as the proliferative phase.

Ans: Primary follicles change into Graafian follicles due to FSH stimulation in the first half of the menstrual cycle. Graafian follicles release estrogens provoking the expansion of the Endometrium of the uterus.

• The second half of the menstrual cycle is called the luteal phase as well as the secretory phase.

Ans: The Corpus luteum is entirely produced and discharges an enormous quantity of Progesterone in the second half of the menstrual cycle.

Q2. State the number of chromosomes in the following cells. Primary oocyte, secondary oocyte, ootid, and follicle.

Ans: The number of chromosomes in the cells is:

• Primary oocytes contain 23 pairs. 
• Secondary oocyte: 23.
•  Ootid: 23. 
•  Follicles contain 23 pairs.

Q3. What is colostrum? State its importance to a newborn baby.

Ans: The milk secreted from mammary glands immediately after birth for 2 or 3 days is known as the colostrum. It is considered to be high in proteins & low in fats. It also consists of the antibody IgA which ensures immunity in newborn infants.

Q4. Where are the Leydig cells situated? What do they release?

Ans: The Leydig cells or interstitial cells are situated in between the seminiferous tubules. Leydig cells release the male sex hormone named ‘testersterone’  which encourages the development of accessory glands & regulates male secondary sexual characteristics.

3 Marks Questions and Answers

Q1. State the male accessory glands and their function.

Ans: The male accessory glands comprise a prostate gland, paired seminal vesicles, and paired bulbourethral glands. These glands release seminal plasma rich in calcium,  fructose, and enzymes. The lubrication of the penis is facilitated by secretions of bulbourethral glands.

Q2. Where does oogenesis occur? Explain the stages of this process.

Ans: Oogenesis is the process of formation & maturation of the ovum. During the embryonic development of the female foetus, this process occurs in the ovary. It comprises three phases:–

1. Multiplication phase:- Oogonia is produced when primordial germ cells split through meiosis. These oogonia divide lay repeated mitotic divisions forming clusters. In each cluster, only one of them enters into the growth phase & is called the primary oocyte.
2. Growth phase:- After the attainment of puberty, the growth phase is initiated. It leads to an increase in the size of the oocyte to several folds & synthesis.
3. Maturation phase:- Two haploids (n) cells are formed as the outcome of the first division is meiotic. In this division, cytokinesis is unequal, a large daughter cell with almost all cytoplasm is known as a secondary oocyte & a smaller me with less cytoplasm is referred to as a polar body. The secondary oocyte then goes through a second meiotic division to form an ovum & a second polar body.

Q3. ‘A fertilised egg is the blueprint of future development’. Explain the statement.

Ans: The father’s genetic information is carried by the sperm in the form of 23 chromosomes (including the male sex chromosome X or Y), whereas the mother’s genetic information is carried by the egg (including the female sex chromosome X). Thus during fertilisation, the fusion of the male and the female gametes produces a new genetic combination that introduces variation in the progeny. The zygote or the fertilised egg contains the genetic information which accordingly controls the development of the embryo.

Q4. A sperm has just fertilised a human egg in the fallopian tube. Write down the events that the fertilised eggs will go through till the implantation of the blastocyst in the uterus.

Ans: 1. Cleavage:- When the zygotes travel through the isthmus of the oviduct, the mitotic division starts which is cleavage approaching the uterus to form 2,4,8,16 daughter cells known as blastomeres. 

2. Blastocyst:- After the process of fertilisation, the morula twins into a large mass of cells known as blastocyst Outer peripheral cells enlarge & flatten further & make trophoblast. Trophoblast cells discharge fluid into the interior & create a cavity named the blastocoel. The embryonic stage with blastocoel is known as a blastula. 

5 Marks Questions and Answers

Q1. What is menstruation? What are the roles of FSH, LH, oestrogen & progesterone in the menstrual cycle?

Ans: On the 28th day of the menstrual cycle due to lack of progesterone, the endometrial lining of the female genital tract breaks down which causes bleeding. This flow of blood that occurs monthly is known as menstruation.

There are a variety of changes that take place in the ovary under the influence of various hormones during the menstrual cycle:-

• Menstrual phase:- The endometrial lining of the uterus breaks down due to very low levels of hormones LH, FSH oestrogen & progesterone.

• Follicular phase:- The release of oestrogen due to an increase in the levels of pituitary hormones FSH & LH, FSH controls the follicular phase, it promotes the growth of follicles. When in the middle of the cycle (14th day) both FSH & LH reach their peak level.

• Ovulatory Phase:– The level of LH hormones reaching its peak (called LH swing) instigates the ruptures of mature Graffian follicle which leads to the release of the ovum.

• Luteal phase:- The LH & FSH hormones start to drastically fall. After ovulation, the follicle ruptures & is converted into the corpus Luteum which releases huge quantities of progesterone.

Human Reproduction Class 12 – Important Questions

Q1. What do the term parturition and lactation mean?

Ans. Parturition is the term used for the process where intense contractions take place before the fully developed foetus is delivered after the end of the pregnancy. Signals of parturition are started by a fully developed foetus and placenta instigating mild uterine contractions. These contractions are called the foetal ejection reflex.

The release of oxytocin is also initiated from the maternal pituitary.

When the mammary glands of a female start producing milk, the term used is referred to as ‘Lactation’. It usually takes place to end the pregnancy. During the initial days of lactation, the milk produced is known as colostrum which consists of many antibodies needed for the baby.

Q2. Explain the organisation of the mammary gland.

Ans. Female mammals have functional mammary glands. These glands differ in individuals and have paired structures, consisting of glandular tissues and fat. The glandular tissue is organised in such a way that it contains 15-20 mammary lobes in each breast, which comprise alveoli which are made up of a cluster of cells. These alveolar cells release the milk that is preserved in the lumens or cavities in the alveoli. The alveoli open into the mammary tubules. These tubules in each of the lobes combine to form the mammary duct. Several mammary ducts come together to form a mammary ampulla that is linked to the lactiferous ducts. Through these structures, milk is sucked.

Q3. What is reproduction?  How do humans reproduce their offspring?

Ans. A biological process of humans reproducing young ones or offspring, who are similar to their parents is called reproduction. Reproduction is done in two distinct modes and is categorised depending on the involvement of the parents.

The two distinct modes of reproduction are:

Asexual Reproduction: Reproduction in this mode requires only one parent and the new offspring produced is genetically identical to the parent.

Sexual Reproduction: Reproduction in this mode involves the formation and shifting of gametes, subsequently leading to fertilisation, the formation of the zygote, and embryogenesis.  

Humans use the sexual mode of reproduction to reproduce their young ones.

Conclusion

Extramarks is a platform where students get to learn about the key concepts and terminologies in Chapter 3 Class 12 Biology Important Questions related to human reproduction. These notes are prepared by Extramarks subject matter experts whose main focus is to facilitate the learning of students and get an overview of the chapter. Students can refer to the Class 12 Biology Chapter 3 Important Questions made by Extramarks to prepare for the board exams.