The periodic abstinence by a couple for family planning should be from:
1
Day 5 to 10 of menstrual cycle
2
Day 13 to 15 of menstrual cycle
3
Day 10 to 17 of menstrual cycle
4
Day 16 to 20 of menstrual cycle
Official Solution
Correct Option: (3)
Periodic abstinence is a natural family planning method in which couples refrain from sexual intercourse during the fertile window of the menstrual cycle to avoid pregnancy. This approach requires an understanding of the woman's menstrual cycle and ovulation patterns. Ovulation, the process of releasing an egg from the ovary, usually occurs on Day 14 of a standard 28-day cycle, though this timing can vary based on individual cycle length. The fertile window, when pregnancy is most likely, includes the days leading up to and immediately following ovulation. This is because sperm can survive up to 5 days in the female reproductive system, and the egg is viable for 12 to 24 hours after ovulation. In a typical 28-day cycle, ovulation happens around Day 14, so it is recommended to abstain from Day 10 to Day 17 to account for potential cycle variations and to reduce the chance of pregnancy. For women with shorter or longer cycles than 28 days, ovulation may occur earlier or later than Day 14, requiring careful tracking of the cycle to adjust the abstinence period.
02
PYQ 2024
medium
biologyID: cbse-cla
Which one of the following hormones is secreted by the human placenta that helps in the maintenance of pregnancy?
1
Relaxin
2
Human Chorionic Gonadotropin
3
Oxytocin
4
Human Placental Lactogen
Official Solution
Correct Option: (2)
Human Chorionic Gonadotropin (hCG) is a hormone secreted by the placenta, playing a crucial role in sustaining pregnancy by supporting the corpus luteum and progesterone production during the early stages. Relaxin is produced later in pregnancy to help relax the pelvic muscles in preparation for delivery. Oxytocin triggers uterine contractions during labor. Human Placental Lactogen aids in fetal growth and metabolism, though it doesn't directly contribute to maintaining pregnancy.
03
PYQ 2024
medium
biologyID: cbse-cla
In humans, the secondary oocyte completes meiotic division when:
1
it gets implanted in the uterine endometrium.
2
it is released from the matured Graafian follicle.
3
it is penetrated by the sperm cell.
4
acrosomal enzymes break down the zona pellucida.
Official Solution
Correct Option: (3)
In humans, the secondary oocyte completes its second meiotic division only after it is penetrated by a sperm cell during fertilization. This step is critical for the oocyte to proceed to form a mature ovum.
Sweden has an age distribution that is approximately of the same width near its base as at the apex. What does this indicate?
Official Solution
Correct Option: (1)
Sweden’s age pyramid indicates: A stable population with low birth and death rates. The percentage of individuals in all age groups is nearly uniform, suggesting a balanced demographic.
06
PYQ 2024
medium
biologyID: cbse-cla
Select the option that gives the correct identification of ovum, morula, and blastocyst in a human female reproduction system as shown in the following diagram:
1
Ovum – B, Morula – D, Blastocyst – F.
2
Ovum – A, Morula – B, Blastocyst – G.
3
Ovum – A, Morula – E, Blastocyst – G.
4
Ovum – B, Morula – D, Blastocyst – G.
Official Solution
Correct Option: (4)
Ovum (B): The unfertilized egg. Morula (D): A solid ball of cells formed after a series of mitotic divisions. Blastocyst (G): A hollow structure in early embryonic development that implants into the uterine wall.
07
PYQ 2024
medium
biologyID: cbse-cla
In a fertilized ovule of an angiosperm, the cells in which n, 2n, and 3n conditions respectively occur are:
1
antipodal, zygote, and endosperm
2
zygote, nucellus, and endosperm
3
endosperm, nucellus, and zygote
4
antipodals, synergids, and integuments
Official Solution
Correct Option: (1)
n (haploid): Found in antipodal cells. 2n (diploid): Found in the zygote formed by fertilization. 3n (triploid): Found in the endosperm formed by double fertilization. This distribution of ploidy levels is a characteristic feature of angiosperm reproduction.
08
PYQ 2024
medium
biologyID: cbse-cla
Explain the processing of heterogeneous nuclear RNA (hnRNA) into a fully functional mRNA in eukaryotes. Where does this processing occur in the cell?
Official Solution
Correct Option: (1)
Steps of Processing:Capping: Addition of a 5 methyl guanosine cap. Splicing: Removal of introns and joining of exons. Polyadenylation: Addition of a poly-A tail at the 3 end. Location: The processing occurs in the nucleus of eukaryotic cells.
09
PYQ 2025
easy
biologyID: cbse-cla
Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.
Official Solution
Correct Option: (1)
Step 1: Two common venereal diseases (VDs) in females are:
Gonorrhoea
Syphilis
Step 2: If left untreated, complications may include:
Pelvic inflammatory disease (PID), which can lead to infertility.
Ectopic pregnancy or damage to reproductive organs.
10
PYQ 2025
easy
biologyID: cbse-cla
Given below are few statements with reference to the uterus in the female reproductive system:
1
The myometrium exhibits strong contractions during the delivery of the baby.
2
The uterus opens into the cervix through a narrow opening called vagina.
3
The cavity of the cervix and the vagina forms the birth canal.
4
The outermost layer of uterus is a thin membranous perimetrium.
Official Solution
Correct Option: (4)
(i) is correct: The myometrium, the muscular layer of the uterus, contracts during childbirth. (ii) is incorrect: The uterus opens into the cervix, which further leads into the vagina, not directly. (iii) is correct: The cervix and vagina together form the birth canal. (iv) is correct: The perimetrium is indeed the outermost thin membranous layer. (v) is incorrect: The uterus is supported by ligaments, not tendons.
11
PYQ 2025
medium
biologyID: cbse-cla
Study the graphs given below for Case 1 and Case 2 showing different levels of certain hormones and answer the question that follows:
(a) Which hormone is responsible for the peak observed in Case 1 and Case 2? Write one function of that hormone. (b) Write changes that take place in the ovary and uterus during follicular phase. Student to attempt either sub-part (c) or (d): (c) Name the hormone Q of Case 2. Write one function of hormone Q. OR (d) Which structure in the ovary will remain functional in Case 2? How is it formed?
Official Solution
Correct Option: (1)
Step 1 (a): The hormone responsible for the peak in both Case 1 and Case 2 is **Luteinizing Hormone (LH)**.
\hspace*{0.5cm} Function: LH stimulates ovulation and formation of corpus luteum. Step 2 (b): During the follicular phase, in the ovary, a primary follicle develops into a Graafian follicle.
In the uterus, the endometrium regenerates under the influence of estrogen. Step 3 (c): Hormone Q in Case 2 is **Progesterone**.
\hspace*{0.5cm} Function: Maintains the endometrial lining for implantation and supports early pregnancy. \begin{center} OR
\end{center} Step 3 (d): The functional structure in Case 2 is the **Corpus luteum**.
\hspace*{0.5cm} It is formed from the Graafian follicle after ovulation under the influence of LH.
12
PYQ 2025
medium
biologyID: cbse-cla
Shyam and Radha are expecting their first child with Radha being in her second month of pregnancy with no complications. Shyam’s family has a history of cystic fibrosis while Radha’s family has a history of Down’s syndrome, leading to a concern that the baby may have one of these conditions. (a) Suggest and explain a way of testing if their baby is at risk for any genetic disorders. (b) In case of presence of one or both of the abnormalities and posing a risk to the mother’s health, mention one possible option for them to consider. Is that option safe for Radha at the current gestational age? Justify. (c) Under what conditions is the process mentioned in (b) illegal?
Official Solution
Correct Option: (1)
Step 1 (a): One way to test for genetic disorders in a developing fetus is through **amniocentesis** or **chorionic villus sampling (CVS)**. These are prenatal diagnostic techniques that help detect chromosomal or genetic abnormalities like Down’s syndrome and cystic fibrosis. Step 2 (b): If abnormalities are confirmed and they pose a severe risk to the fetus or the mother, **medical termination of pregnancy (MTP)** is an option. Justification: MTP is considered safe during the first trimester (up to 12 weeks), and Radha is in her second month (around 8 weeks), which falls within this safe period. Step 3 (c): MTP becomes illegal if: It is performed without the consent of the pregnant woman. It is conducted after the legally permissible gestation period (currently 24 weeks in India) without appropriate medical board approval. It is done for reasons such as sex selection, which is strictly prohibited.
13
PYQ 2025
medium
biologyID: cbse-cla
Assertion (A): Saheli is the World’s first non-steroidal oral contraceptive pill. Reason (R): It has been developed by National Institute of Immunology, New Delhi.
1
Both (A) and (R) are true and (R) is the correct explanation of (A).
2
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3
(A) is true, but (R) is false.
4
(A) is false, but (R) is true.
Official Solution
Correct Option: (1)
Step 1: Saheli is indeed the first non-steroidal oral contraceptive pill and is unique in its action. Step 2: It was developed by the National Institute of Immunology (NII), New Delhi. Step 3: Since both statements are true and the reason directly explains the assertion, option (A) is correct.
14
PYQ 2025
medium
biologyID: cbse-cla
Match the following items of Column-I with that of Column-II:
1
(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
2
(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
3
(a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
4
(a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
Official Solution
Correct Option: (1)
Step 1: Trophoblast is the outer layer of the blastocyst → (a) → (iv) Step 2: Implantation is the embedding of blastocyst into the endometrium → (b) → (i) Step 3: Inner cell mass forms the embryo → (c) → (ii) Step 4: Morula is an embryo stage with 8–16 blastomeres → (d) → (iii)
15
PYQ 2025
medium
biologyID: cbse-cla
Given below are few statements with reference to the ovaries of the human female reproductive system: (i) It is 2--4 cm in length and is connected to the pelvic wall by tendons. (ii) It is covered by a thin epithelium which encloses the ovarian stroma. (iii) The stroma is divided into a peripheral medulla and an inner cortex. (iv) The ovaries are the primary female sex organs that produce the female gamete (ovum). (v) Ovaries are located one on each side of the lower abdomen. Choose the option with all the true statements from the given options:
1
(i), (ii) and (iv)
2
(ii), (iii) and (v)
3
(ii), (iv) and (v)
4
(i), (iii) and (iv)
Official Solution
Correct Option: (1)
Statements (i), (ii), (iv), and (v) are true. The ovaries are 2--4 cm long and are connected to the pelvic wall by ligaments (often referred to as tendons in some contexts), covered by a thin epithelium enclosing the stroma, are the primary female sex organs producing ova, and are located on each side of the lower abdomen. However, statement (iii) is false because the stroma is divided into an outer cortex and an inner medulla, not the other way around. Thus, option (A) with (i), (ii), and (iv) contains all true statements.
16
PYQ 2025
medium
biologyID: cbse-cla
Student to attempt either option (A) or (B): (A) (i) Draw a diagrammatic sectional view of human seminiferous tubule (enlarged) and label the following: (a) Cell that undergoes spermiogenesis (b) Cell that nourish male gametes (c) Cell which undergoes meiosis I and meiosis II. (ii) State what is seminal plasma. Mention two constituents of seminal plasma. How is it different from semen? OR (B) (i) Mention the event that induces the completion of the meiotic division of the secondary oocyte in humans. (ii) Trace the journey of the zygote until its implantation inside the uterus.
Official Solution
Correct Option: (1)
Option (A): Step 1: The diagrammatic sectional view of a human seminiferous tubule should show: (a) Spermatids (undergoing spermiogenesis), (b) Sertoli cells (that nourish the male gametes), and (c) Primary and secondary spermatocytes (undergoing meiosis I and II). Step 2: Seminal plasma is the fluid part of semen secreted by accessory glands (seminal vesicles, prostate gland, and bulbourethral glands). Two constituents of seminal plasma are: (i) Fructose (provides energy to sperm), and (ii) Prostaglandins (aid in sperm motility and uterine contractions). Semen is the combination of seminal plasma and spermatozoa (sperms), whereas seminal plasma refers only to the fluid portion. OR Option (B): Step 3: The event that induces the completion of meiotic division of the secondary oocyte is the entry of the sperm into the ovum during fertilization. This triggers the secondary oocyte to complete meiosis II, forming the ovum and a second polar body. Step 4: Journey of the zygote: After fertilization in the ampullary region of the fallopian tube, the zygote undergoes repeated mitotic divisions (cleavage) forming a blastomere. It moves through the fallopian tube and becomes a morula, then a blastocyst. The blastocyst reaches the uterus and implants itself in the endometrial lining of the uterine wall, typically around the 7th day post-fertilization.
17
PYQ 2025
medium
biologyID: cbse-cla
(a) Abbreviations used for the different modes of assisted reproductive technology are given below. Expand the abbreviations:
(i) ZIFT (ii) ICSI (iii) IUT (iv) GIFT (b) Why is there a statutory ban on Amniocentesis? Give at least two reasons.
Official Solution
Correct Option: (1)
(a) (i) ZIFT – Zygote Intra Fallopian Transfer (ii) ICSI – Intra Cytoplasmic Sperm Injection (iii) IUT – Intra Uterine Transfer (iv) GIFT – Gamete Intra Fallopian Transfer (b) Amniocentesis is banned due to the following reasons: 1. It is often misused for sex determination, leading to female foeticide. 2. It promotes social bias and imbalance in the sex ratio, especially in certain regions.
18
PYQ 2025
medium
biologyID: cbse-cla
Student to attempt either option (A) or (B): (i) Identify ‘P’ and ‘Q’ labelled in the diagram. (ii) Specify the source of the hormone ‘P’ and ‘Q’ marked in the diagram. OR (i) Identify ‘P’ and ‘Q’ labelled in the above diagram. (ii) Write down the role of hormone ‘P’ in both males and females.
Official Solution
Correct Option: (1)
Option (A): Step 1: In the ovarian hormone graph, hormone ‘P’ is progesterone and hormone ‘Q’ is estrogen. Step 2: Progesterone (P) is secreted by the corpus luteum after ovulation. Estrogen (Q) is primarily secreted by the growing follicles (Graafian follicle) in the ovary. OR Option (B): Step 1: In the pituitary hormone graph, hormone ‘P’ is Luteinising Hormone (LH) and hormone ‘Q’ is Follicle Stimulating Hormone (FSH). Step 2: In females, LH triggers ovulation and formation of the corpus luteum. In males, LH stimulates Leydig cells to produce testosterone.
19
PYQ 2025
medium
biologyID: cbse-cla
(a) Name and explain the role of inner and middle walls of the human female uterus. (b) Write the location and function of fimbriae in human female.
Official Solution
Correct Option: (1)
Step 1 (a): The inner and middle walls of the uterus are:
Endometrium (Inner lining): It undergoes cyclic changes during the menstrual cycle and is essential for implantation of the embryo. It provides nourishment to the developing embryo.
Myometrium (Middle muscular layer): It consists of smooth muscle fibers that help in the contraction of the uterus during childbirth and menstrual flow.
Step 2 (b):
Location of fimbriae: Fimbriae are finger-like projections present at the distal end of the fallopian tubes near the ovary.
Function: They help in capturing the ovum released from the ovary and direct it into the fallopian tube.
20
PYQ 2025
easy
biologyID: cbse-cla
Student to attempt either option (A) or (B):
(A) (i) Explain why the milk produced by the mother during the initial days of lactation is considered to be very essential for the newborn infant.
(ii) What is the term used for the milk produced during the initial days of lactation? OR (B) Many children in the metro cities are suffering from a very common exaggerated response of the immune system to certain weak antigens in air.
(i) What is the term used for the above mentioned disease?
(ii) Name the main type of antibody produced by the immune system in response to this disease.
(iii) Which two main inflammation-causing chemicals are produced by the mast cells in such an immune response?
Official Solution
Correct Option: (1)
(A)Step 1: The milk produced in the initial days is rich in antibodies, especially IgA, which provides passive immunity to the infant. Step 2: It helps protect the newborn against infections during early life when the baby’s immune system is still developing. Step 3: The term used for this milk is colostrum. It is yellowish and secreted in small quantities but highly nutritious. OR (B)Step 1: The exaggerated immune response to weak antigens is called allergy. Step 2: The main type of antibody produced during this response is IgE. Step 3: The mast cells release two major chemicals—histamine and serotonin—which cause inflammation.
21
PYQ 2025
medium
biologyID: cbse-cla
Given below are a few statements with respect to spermatogenesis in a human male.
(i) Sperms are released from the seminiferous tubules by the process of spermiation.
(ii) Spermiogenesis involves the maturation of spermatids into sperms.
(iii) Spermatogonia produce spermatids by the process of spermiogenesis.
(iv) Meiosis II in secondary spermatocytes results in the formation of four equal haploid spermatids.
(v) Primary spermatocyte completes the first meiotic division forming two equal, diploid cells called secondary spermatocytes.
Choose the option with all true statements from the given options:
1
(i), (ii) and (iv)
2
(ii), (iii) and (v)
3
(ii), (iv) and (v)
4
(i), (ii) and (iv)
Official Solution
Correct Option: (1)
(i) is correct — spermiation is the release of sperm from Sertoli cells. (ii) is correct — spermiogenesis is the transformation of spermatids into mature sperm. (iv) is correct — secondary spermatocytes undergo meiosis II to form haploid spermatids. (iii) is incorrect — spermatogonia divide mitotically to produce primary spermatocytes, not directly spermatids. (v) is incorrect — primary spermatocytes undergo meiosis I to form secondary spermatocytes, which are haploid, not diploid.
22
PYQ 2025
medium
biologyID: cbse-cla
Assertion (A): Corpus luteum secretes the hormone, progesterone.
Reason (R): Hormone Progesterone is essential for maintenance of the endometrium.
1
Both (A) and (R) are true and (R) is the correct explanation of (A).
2
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3
(A) is true, but (R) is false.
4
(A) is false, but (R) is true.
Official Solution
Correct Option: (1)
Step 1: The corpus luteum, formed after ovulation, secretes progesterone, making Assertion (A) true. Step 2: Progesterone prepares and maintains the endometrium for pregnancy, making Reason (R) true. Step 3: Since progesterone from the corpus luteum directly supports the endometrium, (R) correctly explains (A). Thus, both (A) and (R) are true, and (R) is the correct explanation of (A).
23
PYQ 2025
medium
biologyID: cbse-cla
During the process of oogenesis in human female, the primary oocyte results in the formation of which of the following?
Choose the correct option.
1
Unequal cells — a smaller haploid secondary oocyte and a larger diploid polar body
2
Unequal cells — a larger haploid secondary oocyte and a smaller haploid polar body
3
Unequal cells — a smaller diploid secondary oocyte and a larger haploid polar body
4
Equal cells — a haploid secondary oocyte and a haploid polar body
Official Solution
Correct Option: (2)
During oogenesis, meiosis in the primary oocyte results in an unequal division of cytoplasm, producing a larger haploid secondary oocyte and a smaller haploid polar body. This ensures that the oocyte retains most of the cytoplasmic content for future embryonic development.
24
PYQ 2025
easy
biologyID: cbse-cla
The number of autosomes present in a human secondary spermatocyte
Official Solution
Correct Option: (1)
25
PYQ 2025
medium
biologyID: cbse-cla
Explain the process of formation of placenta in a human female after the implantation of the blastocyst in the endometrium of the uterus.
Official Solution
Correct Option: (1)
Step 1: After implantation, finger-like projections called chorionic villi appear on the trophoblast part of the blastocyst. Step 2: The uterine tissue and maternal blood vessels surround these villi. Step 3: Chorionic villi and uterine tissue combine to form the placenta. Step 4: The placenta facilitates the exchange of nutrients, gases, and wastes between the mother and the embryo and acts as an endocrine tissue by secreting hormones like hCG, progesterone, and estrogens.
26
PYQ 2025
easy
biologyID: cbse-cla
Student to attempt either option (A) or (B): (A) Write two features of an ideal contraceptive. Explain any one natural contraceptive method that makes the chances of conception almost nil.
(B) Explain GIFT and ICSI.
Official Solution
Correct Option: (1)
(A)Step 1: Two features of an ideal contraceptive:
It should be user-friendly, easily available, and reversible.
In this method, the couple avoids coitus during the fertile period of the menstrual cycle (days 10-17).
Since ovulation occurs around the middle of the cycle, avoiding intercourse during this period reduces chances of fertilization.
This method is safe and has no side effects, and if properly followed, chances of conception are almost nil.
(B)Step 1:GIFT (Gamete Intra-Fallopian Transfer)
It is an assisted reproductive technique where ovum and sperms are collected from donors and placed together into the fallopian tube of a woman.
It is used in cases where the fallopian tube is functional and natural fertilization is preferred inside the body.
Step 2:ICSI (Intra-Cytoplasmic Sperm Injection)
In this method, a sperm is directly injected into the cytoplasm of an ovum in laboratory conditions.
It is used in cases of male infertility where the sperm count is very low or motility is poor.
27
PYQ 2025
medium
biologyID: cbse-cla
Given below are few statements with reference to oogenesis in a human female:
An unequal division of the primary oocyte forms a large secondary oocyte and a tiny first polar body.
A couple of thousands of oogonia are formed within each fetal ovary during embryonic development.
Primary oocytes start meiosis-I but it gets arrested temporarily at prophase-I during fetal development.
Fertilisation induces the completion of the meiotic division of the secondary oocyte.
A primary oocyte on meiosis forms an ovum and a polar body.
Choose the option with all true statements from the given options:
1
(i), (ii), (iv)
2
(ii), (iii), (v)
3
(ii), (iv), (v)
4
(i), (iii), (iv)
Official Solution
Correct Option: (4)
(i) True – The primary oocyte undergoes asymmetric division to form a large secondary oocyte and a small polar body. (ii) False – Millions (not just a couple of thousands) of oogonia are formed during fetal development. (iii) True – Primary oocytes begin meiosis-I but are arrested in prophase-I until puberty. (iv) True – Completion of meiosis-II in the secondary oocyte is triggered by fertilisation. (v) False – The primary oocyte forms a secondary oocyte and a polar body; the ovum is only formed after fertilisation.
28
PYQ 2025
medium
biologyID: cbse-cla
Student to attempt either option (A) or (B): (A) Explain what is meant by the term amniocentesis. How is this technique misused in India? OR (B) Name any two VDs which might occur in a human female. State any two complications in a female if it is left untreated.
Official Solution
Correct Option: (1)
(A)Step 1: Amniocentesis is a prenatal diagnostic technique used to detect chromosomal abnormalities in the fetus. Step 2: A small amount of amniotic fluid is withdrawn from the amniotic sac surrounding the fetus using a syringe under ultrasound guidance. Step 3: Misuse in India:
The technique is often misused for sex determination.
This leads to female foeticide, contributing to an imbalanced sex ratio.
OR (B)Step 1: Two common venereal diseases (VDs) in females are:
Gonorrhoea
Syphilis
Step 2: If left untreated, complications may include:
Pelvic inflammatory disease (PID), which can lead to infertility.
Ectopic pregnancy or damage to reproductive organs.
29
PYQ 2025
medium
biologyID: cbse-cla
Assertion (A): Mode of action of pills and implants/injectables is similar. Reason (R): The effective period of pills is much longer as compared to implants/injectables.
1
Both (A) and (R) are true and (R) is the correct explanation of (A).
2
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3
(A) is true, but (R) is false.
4
(A) is false, but (R) is true.
Official Solution
Correct Option: (3)
Both pills and implants/injectables work by releasing hormones to prevent ovulation, hence their mode of action is similar. However, pills need to be taken daily while implants/injectables have a much longer effective period — so the Reason is false.
30
PYQ 2025
medium
biologyID: cbse-cla
Given below are few statements with reference to the major events in the menstrual cycle of a human female:
During the follicular phase, the primary follicles grow to become a Graafian follicle.
Gonadotropins FSH and progesterone stimulate follicular development during the follicular phase.
LH surge induces rupture of Graafian follicle thereby releasing the corpus luteum.
Progesterone released by corpus luteum is essential for maintenance of endometrium.
Both LH and progesterone attain a peak level in the middle of the cycle.
Choose the option with all true statements from the given options:
1
(i), (ii) and (iv)
2
(ii), (iii) and (v)
3
(ii), (iv) and (v)
4
(i), (iii) and (iv)
Official Solution
Correct Option: (4)
Statements (i), (iii), and (iv) are correct:
(i) During the follicular phase, the primary follicles indeed grow to become a Graafian follicle.
(iii) LH surge is responsible for inducing rupture of the Graafian follicle, leading to the release of the ovum and formation of the corpus luteum.
(iv) Progesterone secreted by the corpus luteum is essential for the maintenance of the endometrium.
Statement (ii) is incorrect because progesterone is not involved in follicular development — it acts after ovulation. Statement (v) is incorrect as only LH peaks in the middle of the cycle, while progesterone peaks later in the luteal phase.
31
PYQ 2025
medium
biologyID: cbse-cla
Penetration of the sperm in the ovum is followed by:
1
Formation of first polar body
2
Completion of Meiosis II
3
First Meiosis
4
Dissolution of zona pellucida
Official Solution
Correct Option: (2)
After sperm penetrates the ovum, the secondary oocyte completes Meiosis II, resulting in the formation of the ovum and a second polar body before fertilization is complete.
32
PYQ 2025
hard
biologyID: cbse-cla
Describe the changes in the ovary and the uterus as induced by the changes in the level of pituitary and ovarian hormones during menstrual cycle in a human female.
Official Solution
Correct Option: (1)
The menstrual cycle, approximately 28 days long, is regulated by the interplay of pituitary and ovarian hormones, leading to cyclical changes in the ovary and uterus:
1. Follicular Phase (Ovary) / Menstrual and Proliferative Phase (Uterus):
Pituitary Hormones: FSH stimulates follicular development in the ovary.
Ovarian Hormones: Developing follicles produce increasing levels of estrogen.
Ovary Changes: Primary follicles mature into Graafian follicles.
Uterus Changes: Low hormone levels cause menstruation (shedding of the endometrium). Estrogen then promotes the proliferation and thickening of the endometrium.
2. Ovulatory Phase (Ovary) / End of Proliferative Phase (Uterus):
Pituitary Hormones: A surge in LH triggers ovulation.
Ovary Changes: Release of the ovum from the Graafian follicle.
Uterus Changes: Endometrium continues to thicken due to estrogen.
Pituitary Hormones: LH maintains the corpus luteum.
Ovarian Hormones: Corpus luteum secretes progesterone and estrogen.
Ovary Changes: Formation and maintenance (or degeneration) of the corpus luteum.
Uterus Changes: Progesterone promotes the secretory phase of the endometrium, making it receptive for implantation. If no fertilization occurs, the corpus luteum degenerates, hormone levels drop, and menstruation begins again.
33
PYQ 2025
medium
biologyID: cbse-cla
Student to attempt either option (A) or (B): (A) Write two features of an ideal contraceptive. Explain any one natural contraceptive method that makes the chances of conception almost nil. OR (B) Explain GIFT and ICSI.
Official Solution
Correct Option: (1)
(A)Step 1: Two features of an ideal contraceptive:
It should be user-friendly, easily available, and reversible.
In this method, the couple avoids coitus during the fertile period of the menstrual cycle (days 10-17).
Since ovulation occurs around the middle of the cycle, avoiding intercourse during this period reduces chances of fertilization.
This method is safe and has no side effects, and if properly followed, chances of conception are almost nil.
OR
(B)Step 1:GIFT (Gamete Intra-Fallopian Transfer)
It is an assisted reproductive technique where ovum and sperms are collected from donors and placed together into the fallopian tube of a woman.
It is used in cases where the fallopian tube is functional and natural fertilization is preferred inside the body.
Step 2:ICSI (Intra-Cytoplasmic Sperm Injection)
In this method, a sperm is directly injected into the cytoplasm of an ovum in laboratory conditions.
It is used in cases of male infertility where the sperm count is very low or motility is poor.
34
PYQ 2025
medium
biologyID: cbse-cla
(A)
Distinguish between the two cells enclosed in a mature male gametophyte of an angiosperm. Study the diagram given below showing the modes of pollination. Answer the questions that follow.
The given diagram shows three methods of pollen transfer in plants. Examine them carefully and write the technical terms used for pollen transfer methods ‘1’, ‘2’ and ‘3’. How do the following plants achieve pollination successfully?
Water lily Vallisneria Write advantages of pollen transfer in method ‘3’. \begin{center} OR
\end{center} (B)
Given below is the diagram of human ovum surrounded by a few sperms. Observe the diagram and answer the questions that follow:
Compare the fate of sperms ‘P’, ‘Q’ and ‘R’ shown in the diagram. Write the role of Zona pellucida in this process. Analyse the changes occurring in the ovum after the entry of sperm. How acrosome and middle piece of a human sperm are able to play an important role in human fertilization?
Official Solution
Correct Option: (1)
Step 1 (A):
In a mature male gametophyte of an angiosperm, two cells are enclosed: \begin{itemize} Generative cell: Divides to form two male gametes (sperms). Vegetative cell: Forms the pollen tube for gamete transfer. \end{itemize}
Technical terms: \begin{itemize} 1 — Autogamy 2 — Geitonogamy 3 — Xenogamy \end{itemize} Pollination modes: \begin{itemize} Water lily: By insects (entomophily) Vallisneria: By water (hydrophily) \end{itemize} Advantages of Xenogamy (method ‘3’): \begin{itemize} Introduces genetic variation. Helps in evolution and adaptability. \end{itemize} Step 2 (B):
Fate of sperms: \begin{itemize} P: Fails to penetrate the ovum. Q: Successfully fertilizes the ovum. R: Degenerates. \end{itemize} Role of Zona pellucida: \begin{itemize} It prevents polyspermy by blocking entry of additional sperms once one sperm has penetrated. \end{itemize} Changes after sperm entry: \begin{itemize} Completion of meiosis II. Formation of female pronucleus. Zona reaction to block polyspermy. \end{itemize} Role of acrosome and middle piece: \begin{itemize} Acrosome: Contains enzymes to digest egg membranes. Middle piece: Packed with mitochondria providing energy for sperm motility. \end{itemize}
35
PYQ 2025
medium
biologyID: cbse-cla
Study the graphs given below for Case 1 and Case 2 showing different levels of certain hormones and answer the question that follows: (a) Which hormone is responsible for the peak observed in Case 1 and Case 2? Write one function of that hormone. (b) Write changes that take place in the ovary and uterus during follicular phase. Student to attempt either sub-part (c) or (d): (c) Name the hormone Q of Case 2. Write one function of hormone Q.
\begin{center} OR
\end{center}
(d) Which structure in the ovary will remain functional in Case 2? How is it formed?
Official Solution
Correct Option: (1)
Step 1 (a): The hormone responsible for the peak in both Case 1 and Case 2 is **Luteinizing Hormone (LH)**. Function: LH stimulates ovulation and formation of corpus luteum. Step 2 (b): During the follicular phase, in the ovary, a primary follicle develops into a Graafian follicle.
In the uterus, the endometrium regenerates under the influence of estrogen. Step 3 (c): Hormone Q in Case 2 is **Progesterone**. Function: Maintains the endometrial lining for implantation and supports early pregnancy. \begin{center} OR
\end{center} Step 3 (d): The functional structure in Case 2 is the **Corpus luteum**. It is formed from the Graafian follicle after ovulation under the influence of LH.
36
PYQ 2025
medium
biologyID: cbse-cla
Shyam and Radha are expecting their first child with Radha being in her second month of pregnancy with no complications. Shyam’s family has a history of cystic fibrosis while Radha’s family has a history of Down’s syndrome, leading to a concern that the baby may have one of these conditions. (a) Suggest and explain a way of testing if their baby is at risk for any genetic disorders. (b) In case of presence of one or both of the abnormalities and posing a risk to the mother’s health, mention one possible option for them to consider. Is that option safe for Radha at the current gestational age? Justify. (c) Under what conditions is the process mentioned in (b) illegal?
Official Solution
Correct Option: (1)
Step 1 (a): One way to test for genetic disorders in a developing fetus is through **amniocentesis** or **chorionic villus sampling (CVS)**. These are prenatal diagnostic techniques that help detect chromosomal or genetic abnormalities like Down’s syndrome and cystic fibrosis. Step 2 (b): If abnormalities are confirmed and they pose a severe risk to the fetus or the mother, **medical termination of pregnancy (MTP)** is an option. Justification: MTP is considered safe during the first trimester (up to 12 weeks), and Radha is in her second month (around 8 weeks), which falls within this safe period. Step 3 (c): MTP becomes illegal if:
\begin{itemize} It is performed without the consent of the pregnant woman. It is conducted after the legally permissible gestation period (currently 24 weeks in India) without appropriate medical board approval. It is done for reasons such as sex selection, which is strictly prohibited.
\end{itemize}
37
PYQ 2025
medium
biologyID: cbse-cla
Assertion (A): Saheli is the World’s first non-steroidal oral contraceptive pill. Reason (R): It has been developed by National Institute of Immunology, New Delhi.
1
Both (A) and (R) are true and (R) is the correct explanation of (A).
2
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3
(A) is true, but (R) is false.
4
(A) is false, but (R) is true.
Official Solution
Correct Option: (1)
Step 1: Saheli is indeed the first non-steroidal oral contraceptive pill and is unique in its action. Step 2: It was developed by the National Institute of Immunology (NII), New Delhi. Step 3: Since both statements are true and the reason directly explains the assertion, option (A) is correct.
38
PYQ 2025
medium
biologyID: cbse-cla
Given below are a few statements with reference to the accessory ducts of the human male reproductive system:
[(i)] The seminiferous tubules of the testes open into rete testis then into the vas deferens.
[(ii)] The vasa efferentia leave the testes and open into the epididymis.
[(iii)] The epididymis leads to vas deferens that ascends into the abdomen.
[(iv)] The vas deferens receives a duct from the prostrate gland and opens into the urethra as ejaculatory duct.
[(v)] The urethra originates from the urinary bladder and extends through the penis to its external opening, urethral meatus.
Choose the option with all true statements from the given options:
1
(i), (ii), (iv)
2
(ii), (iii), (v)
3
(ii), (iv), (v)
4
(i), (iii), (iv)
Official Solution
Correct Option: (2)
Statement (i) is incorrect because the seminiferous tubules open into the rete testis, but then into the vasa efferentia, not directly into the vas deferens. Statement (ii) is correct – the vasa efferentia carry sperms from the testes to the epididymis. Statement (iii) is correct – the epididymis leads into the vas deferens, which ascends into the abdominal cavity. Statement (iv) is incorrect – the vas deferens joins with the duct of the seminal vesicle (not the prostate) to form the ejaculatory duct. Statement (v) is correct – the urethra starts from the urinary bladder and ends at the external urethral opening (meatus).
39
PYQ 2025
medium
biologyID: cbse-cla
Menstrual cycle in human females consists of various events. Select the option that indicates the correct sequence of these events of menstrual cycle.
Step 1: The menstrual cycle in human females consists of four main phases that occur in a specific order. Step 2: The cycle begins with the Menstrual phase (shedding of the uterine lining), followed by the Follicular phase (follicle development), then the Ovulatory phase (release of the egg), and finally the Luteal phase (preparation for potential pregnancy). Step 3: Comparing the options, option (B) correctly lists the sequence as Menstrual phase, Follicular phase, Ovulatory phase, and Luteal phase.
Thus, the correct sequence is Menstrual phase, Follicular phase, Ovulatory phase, Luteal phase.
40
PYQ 2025
medium
biologyID: cbse-cla
Explain the neuroendocrine mechanism involved in the process of parturition in a human female leading to the expulsion of the baby out of the uterus through the birth canal.
Official Solution
Correct Option: (1)
Step 1: Parturition is the process of childbirth, initiated by a complex neuroendocrine mechanism. Step 2:
Signals from the fully developed foetus and placenta trigger mild uterine contractions.
These contractions are sensed by the maternal hypothalamus, which signals the posterior pituitary to release oxytocin.
These contractions further stimulate oxytocin release, intensifying the process.
Eventually, this leads to expulsion of the baby through the birth canal.
41
PYQ 2025
medium
biologyID: cbse-cla
Explain what is meant by the term amniocentesis. How is this technique misused in India?
Official Solution
Correct Option: (1)
Step 1: Amniocentesis is a prenatal diagnostic technique used to detect chromosomal abnormalities in the fetus. Step 2: A small amount of amniotic fluid is withdrawn from the amniotic sac surrounding the fetus using a syringe under ultrasound guidance. Step 3: Misuse in India:
The technique is often misused for sex determination.
This leads to female foeticide, contributing to an imbalanced sex ratio.
42
PYQ 2025
hard
biologyID: cbse-cla
Assertion (A): Cu-T, Cu-7 and LNG-20 are the most widely used copper-releasing IUDs. Reason (R): Cu-ions in IUDs effectively suppress sperm motility and the fertilising capacity of sperms.
1
Both (A) and (R) are true and (R) is the correct explanation of (A).
2
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3
(A) is true, but (R) is false.
4
(A) is false, but (R) is true.
Official Solution
Correct Option: (1)
Step 1: Cu-T, Cu-7, and LNG-20 are common IUDs — Assertion is true. Step 2: Copper ions impair sperm motility and fertility — Reason is true. Step 3: This mechanism directly explains the effectiveness of copper IUDs — so (A) is correct.
43
PYQ 2025
medium
biologyID: cbse-cla
Given below are few statements with respect to the process of oogenesis in a human ovary:
(i) Each granulosa cell gets surrounded by a primary oocyte to form the primary follicle.
(ii) A couple of million of oogonia are formed within each fetal ovary during the embryonic development.
(iii) Tertiary follicle is characterised by antrum and theca layers.
(iv) Secondary follicles form a zona pellucida layer around it.
(v) Mature graafian follicle ruptures to release the secondary oocyte from the ovary. Choose the option with all true statements from the given options:
1
(i), (iii), (iv)
2
(ii), (iii), (iv), (v)
3
(ii), (iv), (v)
4
(i), (iii), (v)
Official Solution
Correct Option: (2)
In oogenesis, (i) is incorrect because granulosa cells surround the primary oocyte, not the other way around, to form the primary follicle. (ii) is correct, as around 1–2 million oogonia are formed in each fetal ovary during development. (iii) is correct, as the tertiary follicle has an antrum and theca layers. (iv) is correct, as the zona pellucida forms in the secondary follicle stage. (v) is correct, as the Graafian follicle ruptures to release the secondary oocyte during ovulation.
44
PYQ 2025
medium
biologyID: cbse-cla
(a) (i) Explain how does double fertilisation take place in a flowering plant. (ii) Write the fate of the products of double fertilization in these plants.
OR
(b) (i) Explain the structure of testicular lobules in the human male reproductive system. Name the two types of cells present in the seminiferous tubules and state their role. (ii) Describe the role of hypothalamic hormone GnRH in spermatogenesis.
Official Solution
Correct Option: (1)
(a) (A) Double fertilisation in flowering plants: It is a unique event in angiosperms where two male gametes are involved. One male gamete fuses with the egg cell to form a diploid zygote (syngamy), and the other fuses with the two polar nuclei to form a triploid primary endosperm nucleus (PEN). This process is called triple fusion. Together, syngamy and triple fusion constitute double fertilization. (B) Fate of products: OR (b) (A) Structure of testicular lobules: Each testis has about 250 compartments called testicular lobules. Each lobule contains 1–3 highly coiled seminiferous tubules. These tubules are the sites of spermatogenesis. Two main types of cells are present:(D) Role of GnRH in spermatogenesis: The hypothalamus releases GnRH (Gonadotropin Releasing Hormone), which stimulates the anterior pituitary to secrete:
45
PYQ 2025
medium
biologyID: cbse-cla
Explain the process of formation of placenta in a human female after the implantation of the blastocyst in the endometrium of the uterus.
Official Solution
Correct Option: (1)
Step 1: After implantation, the finger-like projections called chorionic villi develop from the trophoblast (outer layer of the blastocyst) into the surrounding uterine tissue. Step 2: These villi grow into the maternal tissue and are surrounded by blood spaces called lacunae formed in the endometrium. Step 3: The chorionic villi and uterine tissue together form a structural and functional unit called the placenta. Step 4: Placenta acts as a nutritive, respiratory, excretory, and endocrine organ. It facilitates the exchange of oxygen, nutrients, and waste between mother and foetus.
46
PYQ 2025
medium
biologyID: cbse-cla
Assertion (A): ‘Saheli’, an oral contraceptive inhibits ovulation and increases phagocytosis of sperms. Reason (R): It is a non-steroidal preparation.
1
Both (A) and (R) are true and (R) is the correct explanation of (A).
2
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
3
(A) is true, but (R) is false.
4
(A) is false, but (R) is true.
Official Solution
Correct Option: (2)
Step 1: ‘Saheli’ is a non-steroidal oral contraceptive that contains Centchroman. Step 2: It works by preventing ovulation and also by making the uterus less receptive to implantation. Step 3: While both statements are true, being non-steroidal is not the reason for inhibiting ovulation and increasing phagocytosis of sperms.
47
PYQ 2025
medium
biologyID: cbse-cla
Match the following items of Column-I with that of Column-II:
Column-I
Column-II
(a) Trophoblast
(iv) Outer layer of blastocyst
(b) Implantation
(i) Embedding of blastocyst in the endometrium
(c) Inner cell mass
(ii) Group of cells that would differentiate as embryo
(d) Morula
(iii) Embryo with 8–16 blastomeres
Choose the option that matches Column-I with Column-II correctly:
1
A
2
B
3
C
4
D
Official Solution
Correct Option: (1)
Step 1: Trophoblast is the outer layer of the blastocyst → (a) → (iv) Step 2: Implantation is the embedding of blastocyst into the endometrium → (b) → (i) Step 3: Inner cell mass forms the embryo → (c) → (ii) Step 4: Morula is an embryo stage with 8–16 blastomeres → (d) → (iii)
48
PYQ 2025
medium
biologyID: cbse-cla
How is the interaction between and its specific bee pollinator one of the best examples of co-evolution? Explain.
Official Solution
Correct Option: (1)
The Co-evolution of the Orchid Ophrys and Its Bee Pollinator
The interaction between the orchid genus Ophrys and its specific bee pollinator is a remarkable example of co-evolution. The orchid has evolved to exhibit floral mimicry of the female bee in terms of its appearance, scent, and touch. This mimicry deceives the male bee into attempting to mate with the flower (pseudocopulation). During this process, the pollinia (pollen sacs) of the Ophrys flower get attached to the bee’s body. When the same bee visits another Ophrys flower, it transfers the pollinia, thus achieving pollination.
This close relationship has driven the co-evolution of both the orchid and the bee in the following ways:
Floral Mimicry: Over evolutionary time, Ophrys flowers have developed intricate shapes, colors, and textures that closely resemble the female bee of a specific species. This visual mimicry attracts the male bee.
Scent Mimicry: The orchid flowers also emit volatile chemicals (pheromones) that mimic the sex pheromones of the female bee, further enticing the male bee.
Timing of Flowering:Ophrys species often flower at a time when the specific female bee emerges, maximizing the chances of pollination by the corresponding male bee.
Bee Behavior: The male bee’s mating behavior and preferences have, in turn, influenced the selection pressures on the orchid’s floral traits. Only those orchids that most effectively mimic the female bee are successfully pollinated, passing on their genes.
This intricate, species-specific mimicry highlights a tight co-evolutionary relationship where the reproductive success of the orchid is entirely dependent on the deception of a single bee species. The bee’s behavior exerts strong selective pressure on the orchid’s floral characteristics. The high degree of specialization makes this interaction a classic illustration of co-evolution.
Correct Answer:
The interaction demonstrates co-evolution through the orchid’s floral mimicry (appearance, scent, touch) of the specific female bee, leading to pseudocopulation and pollination. This has resulted in reciprocal evolutionary changes in both the orchid and the bee.
49
PYQ 2025
medium
biologyID: cbse-cla
Given below are a few statements with reference to the human sperm. 1. Sperm head contains a large nucleus and a lot of cytoplasm. 2. Mitochondria in the middle piece of a sperm provides ATP for the sperm motility.
3. Posterior part of the sperm head is covered by acrosome.
4. Spermatids undergo maturation into spermatozoa by the process of spermiogenesis.
5. Acrosomal secretions help in the entry of the sperm into the ovum at the time of fertilization. Choose the option with all true statements from the given options :
1
(i), (ii) and (iv)
2
(ii), (iii) and (v)
3
(ii), (iv) and (v)
4
(i), (iii) and (iv)
Official Solution
Correct Option: (3)
Let's evaluate each statement about the human sperm:
(A) Sperm head contains a large nucleus and a lot of cytoplasm. This statement is incorrect. The sperm head primarily contains a haploid nucleus with very little cytoplasm.
(B) Mitochondria in the middle piece of a sperm provides ATP for the sperm motility. This statement is correct. The middle piece contains numerous mitochondria that produce energy (ATP) required for the movement of the sperm's tail.
(C) Posterior part of the sperm head is covered by acrosome. This statement is incorrect. The acrosome is a cap-like structure present at the anterior part of the sperm head.
(D) Spermatids undergo maturation into spermatozoa by the process of spermiogenesis. This statement is correct. Spermiogenesis is the transformation of spermatids into mature, motile spermatozoa.
(E) Acrosomal secretions help in the entry of the sperm into the ovum at the time of fertilization. This statement is correct. The acrosome contains enzymes that help the sperm penetrate the zona pellucida of the ovum during fertilization. Therefore, the true statements are (ii), (iv), and (v).
50
PYQ 2025
medium
biologyID: cbse-cla
Write the location and function of fimbriae in human female.
Official Solution
Correct Option: (1)
Location: Fimbriae are finger-like projections located at the distal end (closest to the ovary) of the fallopian tubes (also known as oviducts). They surround the opening of the fallopian tube, which is situated near the ovary but not directly attached to it. Function: The primary function of the fimbriae is to catch the ovulated ovum (egg) when it is released from the ovary during ovulation. At the time of ovulation, the fimbriae become more active and sweep over the surface of the ovary. The cilia (hair-like structures) on the surface of the fimbriae create currents in the peritoneal fluid that help to draw the released ovum into the infundibulum (the funnel-shaped opening) of the fallopian tube. Once inside the fallopian tube, the ovum can be fertilized by sperm. The fimbriae ensure that the ovum does not get lost in the abdominal cavity and is successfully transported into the female reproductive tract for potential fertilization. Correct Answer : Fimbriae are finger-like projections at the open end of the fallopian tubes near the ovary. Their function is to catch the ovulated ovum and guide it into the fallopian tube
51
PYQ 2025
medium
biologyID: cbse-cla
Explain the beneficial role of the following, produced as a result of the processes of biotechnology, to mankind: Cow named Rosie
Official Solution
Correct Option: (1)
The cow named Rosie was the first transgenic cow to produce human protein-enriched milk. This was achieved through genetic engineering, where the gene encoding the human alpha-lactalbumin protein was introduced into Rosie’s genome. As a result, Rosie’s milk contained the human alpha-lactalbumin protein at a concentration of about 2.4 grams per liter. The beneficial role of Rosie’s milk to mankind is significant, particularly for human infants. Human milk is nutritionally superior to natural cow milk for human babies, and alpha-lactalbumin is a major protein in human milk. Milk enriched with human alpha-lactalbumin is more nutritionally balanced for human infants and is closer in composition to natural human breast milk. This can lead to: Improved nutritional value: Providing essential amino acids and a more balanced protein profile for infant growth and development. Enhanced digestibility: Making the milk easier for infants to digest compared to regular cow milk. Potential health benefits: Alpha-lactalbumin has also been shown to have some prebiotic properties and may play a role in infant gut health. Rosie’s creation demonstrated the potential of transgenic animals to produce biologically important human proteins, paving the way for the development of other transgenic animals for pharmaceutical production (molecular farming) and improved food quality. Correct Answer : Cow Rosie was the first transgenic cow to produce milk enriched with human alpha-lactalbumin protein. This milk is more nutritionally balanced and easier to digest for human infants, bringing it closer in composition to natural human breast milk and offering potential health benefits.
52
PYQ 2025
medium
biologyID: cbse-cla
Given below are few statements with reference to the human male reproductive system: 1. Paired seminal vesicles, prostate gland and bulbourethral gland constitute the male accessory glands. 2. Secretions of the male accessory glands constitute the seminal plasma. 3. Secretions of the bulbourethral glands help in the lubrication of the penis. 4. Enlarged end of the the penis is known as foreskin. 5. Seminal plasma is rich in fructose, calcium and certain enzymes. Choose the option with all true statements from the given options:
1
( \text{(i), (ii) and (iv)} )
2
( \text{(ii), (iii) and (v)} )
3
( \text{(ii), (iv) and (v)} )
4
( \text{(i), (iii) and (v)} ) \
Official Solution
Correct Option: (2)
Let's evaluate each statement:
(i) Paired seminal vesicles, prostate gland, and bulbourethral glands are indeed the male accessory glands. So, statement (i) is true. (ii) The secretions from these accessory glands, along with the sperm produced in the testes, together form the seminal plasma. So, statement (ii) is true. (iii) The bulbourethral glands secrete a lubricating fluid that helps in the lubrication of the penis during sexual activity. So, statement (iii) is true. (iv) The enlarged end of the penis is called the glans penis, and it is covered by a loose fold of skin called the foreskin or prepuce. Therefore, statement (iv) is false. (v) Seminal plasma is rich in fructose (which provides energy for sperm motility), calcium, and various enzymes that aid in sperm function. So, statement (v) is true. Therefore, the true statements are (ii), (iii), and (v).
53
PYQ 2026
medium
biologyID: cbse-cla
Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site where fertilization takes place.
Official Solution
Correct Option: (1)
Step 1: Understanding the Concept: Fertilization is the fusion of a haploid sperm with a haploid ovum to form a diploid zygote. This process initiates a series of developmental stages as the embryo moves towards the uterus for attachment. Step 2: Detailed Explanation: 1. Site of Fertilization: Fertilization usually occurs in the ampullary-isthmic junction of the fallopian tube (oviduct). 2. Zygote Formation: The fusion of gametes results in a single-celled diploid zygote. 3. Cleavage: As the zygote moves through the isthmus towards the uterus, it undergoes rapid mitotic divisions called cleavage. It forms 2, 4, 8, and then 16 daughter cells called blastomeres. 4. Morula: The embryo with 8 to 16 blastomeres is called a morula. 5. Blastocyst Formation: The morula continues to divide and transforms into a blastocyst as it enters the uterus. The blastomeres in the blastocyst are arranged into an outer layer called the trophoblast and an inner group of cells attached to the trophoblast called the inner cell mass. 6. Implantation: The trophoblast layer gets attached to the endometrium, and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and cover the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus. This is called implantation. Step 3: Final Answer: The site is the ampullary-isthmic junction. The zygote undergoes cleavage to form a morula, then a blastocyst, which finally implants into the uterine endometrium.
54
PYQ 2026
medium
biologyID: cbse-cla
Which connective tissue connects ovary to pelvic wall and uterus?
1
Tendons
2
Ligaments
3
Cartilage
4
Bone
Official Solution
Correct Option: (2)
Step 1: Understanding the Concept: The ovaries are the primary female sex organs. They must be held in a specific position within the pelvic cavity to function correctly. Step 2: Detailed Explanation: The ovaries are located one on each side of the lower abdomen. Each ovary is connected to the pelvic wall and the uterus by ligaments. Specifically, the ovarian ligament attaches the ovary to the uterus, and the suspensory ligament attaches it to the pelvic wall. (A) Tendons connect muscle to bone. (C) Cartilage is a flexible skeletal tissue. (D) Bone is a hard skeletal tissue. Step 3: Final Answer: Ligaments are the connective tissues responsible for anchoring the ovaries. Option (B) is correct.
55
PYQ 2026
medium
biologyID: cbse-cla
Select the option that shows correct statements : (i) Corpus luteum secretes progesterone. (ii) Only FSH attains a peak level in middle of cycle. (iii) LH surge induces rupture of graafian follicle. (iv) Luteal phase of menstrual cycle is also called proliferative phase.
1
Only (ii) is correct.
2
(i) and (iii) are correct.
3
Only (iv) is correct.
4
(ii) and (iv) are correct.
Official Solution
Correct Option: (2)
Step 1: Understanding the Concept: The human menstrual cycle is regulated by pituitary hormones (LH and FSH) and ovarian hormones (estrogen and progesterone). Understanding the timing of these hormone peaks and the functions of structures like the corpus luteum is essential for identifying the correct statements. Step 2: Detailed Explanation: Let us evaluate each statement based on physiological facts: (i) Corpus luteum secretes progesterone: After ovulation, the ruptured Graafian follicle transforms into the corpus luteum, which acts as a temporary endocrine gland and secretes large amounts of progesterone to maintain the uterine lining. This statement is correct. (ii) Only FSH attains a peak level in middle of cycle: This is incorrect. Both LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone) attain a peak level in the middle of the cycle (around day 14). (iii) LH surge induces rupture of graafian follicle: The rapid secretion of LH leading to its maximum concentration during the mid-cycle is called the LH surge. It induces the rupture of the Graafian follicle and thereby the release of the ovum (ovulation). This statement is correct. (iv) Luteal phase of menstrual cycle is also called proliferative phase: This is incorrect. The luteal phase is also known as the secretory phase. The proliferative phase is another name for the follicular phase. Since statements (i) and (iii) are correct, the correct option is (B). Step 3: Final Answer: Statements (i) and (iii) are the only correct statements among the given choices.
56
PYQ 2026
medium
biologyID: cbse-cla
Identify the stage of follicle where primary oocyte undergoes first meiotic division. Also mention the products of this division.
Official Solution
Correct Option: (1)
Step 1: Understanding the Concept: Oogenesis is the process of formation of a mature female gamete. It involves unequal meiotic divisions occurring within specific stages of ovarian follicles. Step 2: Detailed Explanation: The primary oocyte within the tertiary follicle grows in size and completes its first meiotic division (Meiosis I). This division is unequal, resulting in the formation of: 1. A large haploid secondary oocyte that retains the bulk of the nutrient-rich cytoplasm. 2. A tiny first polar body which usually degenerates. The tertiary follicle then matures into the Graafian follicle. Step 3: Final Answer: Stage: Tertiary follicle. Products: Secondary oocyte and first polar body.
57
PYQ 2026
medium
biologyID: cbse-cla
Briefly explain the events of fertilisation and implantation in an adult human female.
Official Solution
Correct Option: (1)
Step 1: Fertilization.
Fertilization in humans occurs when a sperm cell from the male merges with an egg cell from the female, usually in the fallopian tube. This results in the formation of a zygote, which contains the complete set of chromosomes. Step 2: Formation of Blastocyst.
The zygote divides through mitosis to form a blastocyst, which is a ball of cells. The blastocyst travels through the fallopian tube to the uterus. Step 3: Implantation.
Once in the uterus, the blastocyst attaches to the uterine lining (endometrium). This process, called implantation, is essential for the embryo to receive nutrients and oxygen from the mother for further development.
