Grey crescent is the area
at the point of entry of sperm into ovum
just opposite to the site of entry of sperm into ovum
at the animal pole
at the vegetal pole
The Correct Option is B
Solution and Explanation
The gray crescent is a structural feature that emerges on the side of a frog egg opposite to where the sperm enters. This region contains a cluster of growth factors that essentially control the determination of specific body parts during development. It represents a cortical area in newly fertilized frog eggs, as well as in certain salamanders, forming shortly after fertilization on the side opposite to where the sperm penetrates.
So, the correct option is (B): just opposite to the site of entry of sperm into ovum
Top Questions on Human Reproduction
Arrange the following events in the correct order pertaining to fertilization in the human reproductive system.
(A) The blastocyst becomes embedded in the endometrium.
(B) Finger-like projections appear on the trophoblast called chorionic villi.
(C) The blastomeres are arranged into trophoblast and the inner cell mass.
(D) The zygote divides mitotically and transforms into an embryo with 8-16 blastomeres, called a morula.
- CUET (UG) - 2025
- Biology
- Human Reproduction
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?- CBSE CLASS XII - 2025
- Biology
- Human Reproduction
- 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?- CBSE CLASS XII - 2025
- Biology
- Human Reproduction
- 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.- CBSE CLASS XII - 2025
- Biology
- Human Reproduction
Match the following items of Column-I with that of Column-II:
- CBSE CLASS XII - 2025
- Biology
- Human Reproduction
Concepts Used:
Infertility
Infertility is described as not being able to get pregnant in spite of having frequent, unprotected sex for not less than a year for most couples. Infertility may result from an issue with either you or your partner or a combination of factors that stops a pregnancy.
Symptoms:
The major symptom of infertility is not getting pregnant. There may be no other apparent symptoms. Sometimes, women with infertility may have irregular or missing menstrual periods. In some cases, men with infertility may have some signs of hormonal issues, like changes in hair growth or sexual function.
Causes of male infertility:
- Abnormal sperm production or function
- Problems with the delivery of sperm
- Overexposure to certain environmental factors
- Damage related to cancer and its treatment
Causes of female infertility
- Ovulation disorders
- Uterine or cervical abnormalities
- Fallopian tube damage or blockage
- Endometriosis
- Primary ovarian insufficiency
- Pelvic adhesions
- Cancer and its treatment.