When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One matured egg is released every month by one of the ovaries. The two oviducts unite into an elastic bag-like structure known as uterus.
(a) Write the site of fertilization in human female. [1]
(b) How does the uterus prepare itself to receive and nurture the growing embryo? Explain. [1]
(c) (i) What happens when the egg is not fertilized? [2]
OR
(c) (ii) How does the developing embryo get nutrition from the mother's blood? Explain. [2]
When a girl is born, the ovaries already contain thousands of immature eggs. On reaching puberty, some of these start maturing. One matured egg is released every month by one of the ovaries. The two oviducts unite into an elastic bag-like structure known as uterus.
(a) Write the site of fertilization in human female. [1]
(b) How does the uterus prepare itself to receive and nurture the growing embryo? Explain. [1]
(c) (i) What happens when the egg is not fertilized? [2]
OR
(c) (ii) How does the developing embryo get nutrition from the mother's blood? Explain. [2]
(a) Site of fertilisation: Fertilisation in human females occurs in the oviduct (fallopian tube). The sperms travel upward through the vagina and uterus and reach the oviduct, where they may encounter and fuse with the egg.
(b) Preparation of the uterus: Since the ovary releases one egg every month, the uterus prepares itself every month to receive and nurture a possible embryo. Its lining thickens and becomes richly supplied with blood, so that it can nourish a growing embryo if fertilisation and implantation occur.
(c) (i) What happens when the egg is not fertilised?
If the egg is not fertilised, it survives for about one day. Since the thickened, blood-rich uterine lining built up that month is no longer needed (as there is no embryo to nourish), it slowly breaks down and is shed from the body through the vagina as blood and mucus. This shedding is called menstruation, occurs roughly every month, and usually lasts about two to eight days.
OR
(c) (ii) How does the developing embryo get nutrition from the mother's blood?
The embryo obtains nutrition from the mother's blood through a special tissue called the placenta, a disc embedded in the wall of the uterus. It contains villi (finger-like projections) on the embryo's side, surrounded by blood spaces on the mother's side. This arrangement provides a large surface area through which glucose and oxygen pass from the mother's blood to the embryo. Waste substances generated by the developing embryo are removed by transferring them into the mother's blood through the same placental connection.
Marking Scheme
- 1(a) 1 mark for correctly naming oviduct/fallopian tube
- 2(b) 1 mark for explaining lining thickening and increased blood supply
- 3(c)(i) 2 marks: 1 for egg surviving ~1 day and lining being unnecessary, 1 for describing the breakdown/shedding as menstruation
- 4OR (c)(ii) 2 marks: 1 for identifying the placenta with villi and blood spaces, 1 for explaining exchange of glucose/oxygen (and waste removal)
Hint
Trace the journey: sperm meets egg in the oviduct; the uterus readies its lining every month regardless of outcome; only one of the two possible outcomes — menstruation or placental nourishment — happens depending on fertilisation.
Quick Oral Answer
Fertilisation happens in the oviduct; every month the uterus thickens its lining in readiness for a possible embryo. If fertilisation fails, that lining sheds as menstruation; if it succeeds, the placenta's villi (surrounded by maternal blood spaces) let glucose, oxygen and waste pass between mother and embryo.
Analysis & Explanation
This case-based question is built directly from Section 7.3.3(b) and 7.3.3(c) of the chapter, which describe the female reproductive system, the monthly cycle of uterine preparation, fertilisation, menstruation, and placental nutrition.
(a) The chapter states plainly: "The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg" — hence fertilisation happens in the oviduct/fallopian tube, not the ovary or uterus.
(b) The text explicitly explains that "the uterus prepares itself every month to receive and nurture the growing embryo. The lining thickens and is richly supplied with blood to nourish the growing embryo" — this monthly readiness is hormonally driven and occurs whether or not fertilisation actually takes place.
(c)(i) directly follows Section 7.3.3(c): unfertilised eggs live about a day, and since the thickened lining is now unnecessary, it breaks down and is expelled as the menstrual flow — a cycle that recurs roughly monthly.
(c)(ii) draws on the placenta description in Section 7.3.3(b): the villi–blood space arrangement at the placenta maximises surface area for the two-way exchange of nutrients/oxygen (mother to embryo) and waste (embryo to mother), functionally connecting embryo circulation to maternal circulation without direct mixing of blood.
Common Mistakes
- 1Stating the ovary or uterus (instead of the oviduct) as the fertilisation site
- 2Describing menstruation as happening 'because of' the egg itself rather than the breakdown of the unused thickened uterine lining
- 3For placenta, forgetting that waste removal from embryo to mother also happens via the same villi-blood space structure, not just nutrient delivery
Interesting Facts
The menstrual cycle recurring roughly every month is directly tied to the monthly release of one egg from an ovary — a rhythm the chapter links to the uterus's cyclical preparation for a possible pregnancy.
The placenta allows nutrient and gas exchange between mother and embryo without their blood actually mixing, since the villi are bathed in maternal blood spaces rather than being directly connected to maternal vessels.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2025?
This question carries 4 marks in the CBSE Class 10 Science 2025 examination.
Which chapter does this question come from in Science?
This question is from the chapter "How do Organisms Reproduce?" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Female Reproductive System — Fertilisation, Uterus, Menstruation, Placenta" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2025 paper?
This question appears in Section E in the CBSE Class 10 Science 2025 paper.