How Do Organisms Reproduce? | Fertilisation, Implantation and Pregnancy
Class 10 Science | Chapter 7 | CBSE + Foundation + Competitive
Fertilisation • Zygote • Embryo • Implantation • Placenta • Pregnancy
How Do Organisms Reproduce? | Fertilisation, Implantation and Pregnancy
1. Introduction | परिचय
Fertilisation is the process in which the male gamete (sperm) fuses with the female gamete (ovum) to form a zygote.
निषेचन (Fertilisation) वह प्रक्रिया है जिसमें नर युग्मक (शुक्राणु) और मादा युग्मक (अंडाणु) का संलयन होकर युग्मनज (Zygote) बनता है।
निषेचन (Fertilisation) वह प्रक्रिया है जिसमें नर युग्मक (शुक्राणु) और मादा युग्मक (अंडाणु) का संलयन होकर युग्मनज (Zygote) बनता है।
Sperm + Ovum → Zygote
शुक्राणु + अंडाणु → युग्मनज
शुक्राणु + अंडाणु → युग्मनज
In human beings, fertilisation normally occurs in the fallopian tube (oviduct), not in the uterus.
मनुष्य में सामान्यतः निषेचन फैलोपियन ट्यूब (अंडवाहिनी) में होता है, गर्भाशय में नहीं।
मनुष्य में सामान्यतः निषेचन फैलोपियन ट्यूब (अंडवाहिनी) में होता है, गर्भाशय में नहीं।
CBSE Golden Point: Do not confuse fertilisation with implantation.
Fertilisation = formation of zygote.
Implantation = attachment of embryo to the uterine lining.
Fertilisation = formation of zygote.
Implantation = attachment of embryo to the uterine lining.
2. Gametes and Chromosome Number | युग्मक एवं गुणसूत्र संख्या
| Cell / कोशिका | Chromosome Number | Type |
|---|---|---|
| Human body cell / मानव शरीर कोशिका | 46 | Diploid (2n) |
| Sperm / शुक्राणु | 23 | Haploid (n) |
| Ovum / अंडाणु | 23 | Haploid (n) |
| Zygote / युग्मनज | 46 | Diploid (2n) |
23 + 23 = 46
The reduction of chromosome number in gametes is important because fertilisation restores the diploid chromosome number.
युग्मकों में गुणसूत्र संख्या आधी होने के कारण निषेचन के बाद सामान्य द्विगुणित गुणसूत्र संख्या पुनः स्थापित हो जाती है।
युग्मकों में गुणसूत्र संख्या आधी होने के कारण निषेचन के बाद सामान्य द्विगुणित गुणसूत्र संख्या पुनः स्थापित हो जाती है।
3. Fertilisation in Humans | मनुष्य में निषेचन
Ovulation
अंडोत्सर्जन
अंडोत्सर्जन
→
Sperm reaches
Fallopian Tube
Fallopian Tube
→
Fusion of Gametes
→
Zygote
During ovulation, an ovum is released from an ovary. Sperm deposited in the female reproductive tract can travel through the cervix and uterus towards the fallopian tube.
अंडोत्सर्जन के दौरान अंडाशय से अंडाणु निकलता है। महिला प्रजनन तंत्र में प्रवेश किए हुए शुक्राणु गर्भाशय ग्रीवा और गर्भाशय से होते हुए फैलोपियन ट्यूब तक पहुँच सकते हैं।
अंडोत्सर्जन के दौरान अंडाशय से अंडाणु निकलता है। महिला प्रजनन तंत्र में प्रवेश किए हुए शुक्राणु गर्भाशय ग्रीवा और गर्भाशय से होते हुए फैलोपियन ट्यूब तक पहुँच सकते हैं।
If a sperm successfully fuses with the ovum, fertilisation occurs and a zygote is formed.
यदि कोई शुक्राणु अंडाणु से सफलतापूर्वक संलयित हो जाता है, तो निषेचन होता है और युग्मनज बनता है।
यदि कोई शुक्राणु अंडाणु से सफलतापूर्वक संलयित हो जाता है, तो निषेचन होता है और युग्मनज बनता है।
Important: Only one sperm normally fertilises the ovum. After fertilisation, mechanisms prevent additional sperm from entering the egg.
4. Fertilisation to Implantation – Animated Diagram
5. Development of Zygote | युग्मनज का विकास
Zygote
→
Cell Division
→
Embryo
→
Implantation
→
Foetus
After fertilisation, the zygote begins repeated cell divisions. As development continues, the group of cells becomes an embryo.
निषेचन के बाद युग्मनज में बार-बार कोशिका विभाजन होता है। विकास के साथ कोशिकाओं का समूह भ्रूण (Embryo) में विकसित होता है।
निषेचन के बाद युग्मनज में बार-बार कोशिका विभाजन होता है। विकास के साथ कोशिकाओं का समूह भ्रूण (Embryo) में विकसित होता है।
The developing embryo moves towards the uterus and becomes attached to the thickened lining of the uterus.
विकसित होता भ्रूण गर्भाशय की ओर जाता है और गर्भाशय की मोटी हुई आंतरिक परत से जुड़ जाता है।
विकसित होता भ्रूण गर्भाशय की ओर जाता है और गर्भाशय की मोटी हुई आंतरिक परत से जुड़ जाता है।
6. Implantation | आरोपण
Implantation is the process by which the developing embryo becomes attached to the lining of the uterus, called the endometrium.
आरोपण (Implantation) वह प्रक्रिया है जिसमें विकसित होता हुआ भ्रूण गर्भाशय की आंतरिक परत एंडोमेट्रियम से जुड़ जाता है।
आरोपण (Implantation) वह प्रक्रिया है जिसमें विकसित होता हुआ भ्रूण गर्भाशय की आंतरिक परत एंडोमेट्रियम से जुड़ जाता है।
Fertilisation → Zygote → Cell Division → Embryo → Implantation
Remember:
Fertilisation occurs in the fallopian tube.
Implantation occurs in the uterus.
Fertilisation occurs in the fallopian tube.
Implantation occurs in the uterus.
The uterine lining becomes thick and richly supplied with blood vessels so that it can support the developing embryo.
7. Pregnancy | गर्भावस्था
Pregnancy begins after successful implantation and establishment of the developing embryo in the uterus.
सफल आरोपण और गर्भाशय में भ्रूण के विकास के साथ गर्भावस्था की स्थापना होती है।
सफल आरोपण और गर्भाशय में भ्रूण के विकास के साथ गर्भावस्था की स्थापना होती है।
During pregnancy, the embryo undergoes extensive growth and differentiation. As development progresses, the developing baby is commonly called a foetus after the early embryonic stage.
गर्भावस्था के दौरान भ्रूण में तीव्र वृद्धि और विभेदन होता है। प्रारंभिक भ्रूणीय अवस्था के बाद विकसित हो रहे शिशु को सामान्यतः भ्रूण (Foetus) कहा जाता है।
गर्भावस्था के दौरान भ्रूण में तीव्र वृद्धि और विभेदन होता है। प्रारंभिक भ्रूणीय अवस्था के बाद विकसित हो रहे शिशु को सामान्यतः भ्रूण (Foetus) कहा जाता है।
8. Placenta | अपरा / प्लेसेंटा
The placenta is a specialised temporary organ that develops between maternal and foetal tissues during pregnancy.
प्लेसेंटा गर्भावस्था के दौरान मातृ और भ्रूणीय ऊतकों के बीच बनने वाला एक विशेष अस्थायी अंग है।
प्लेसेंटा गर्भावस्था के दौरान मातृ और भ्रूणीय ऊतकों के बीच बनने वाला एक विशेष अस्थायी अंग है।
It provides a large surface for exchange of materials between the mother and developing foetus.
यह माँ और विकसित होते भ्रूण के बीच पदार्थों के आदान-प्रदान के लिए एक बड़ा सतह क्षेत्र प्रदान करता है।
यह माँ और विकसित होते भ्रूण के बीच पदार्थों के आदान-प्रदान के लिए एक बड़ा सतह क्षेत्र प्रदान करता है।
| Substance | General Direction |
|---|---|
| Oxygen | Mother → Foetus |
| Nutrients | Mother → Foetus |
| Carbon dioxide | Foetus → Mother |
| Some metabolic wastes | Foetus → Mother |
Maternal and foetal blood do not normally mix directly; exchange occurs across the placental interface.
9. Hormonal Support During Pregnancy | गर्भावस्था में हार्मोनल भूमिका
After ovulation, the corpus luteum produces progesterone, which helps maintain the uterine lining.
During pregnancy, the placenta also becomes an important endocrine tissue and produces hormones that help maintain pregnancy and prepare the mother's body for childbirth and lactation.
| Hormone | Main Role |
|---|---|
| Progesterone | Helps maintain uterine lining |
| Estrogen | Supports growth of reproductive tissues and pregnancy-related changes |
| hCG | Supports corpus luteum during early pregnancy |
| hCG is also detected in pregnancy tests | Useful marker of pregnancy |
10. What Happens if Fertilisation Does Not Occur?
No Fertilisation
→
Corpus Luteum Degenerates
→
Hormone Levels Fall
→
Uterine Lining Breaks Down
→
Menstruation
If fertilisation does not occur, the uterine lining is no longer maintained at the same level. Hormonal changes lead to its shedding, resulting in menstruation.
यदि निषेचन नहीं होता है, तो हार्मोनल परिवर्तन के कारण गर्भाशय की परत टूटकर बाहर निकलती है, जिसे मासिक धर्म कहते हैं।
यदि निषेचन नहीं होता है, तो हार्मोनल परिवर्तन के कारण गर्भाशय की परत टूटकर बाहर निकलती है, जिसे मासिक धर्म कहते हैं।
11. Fertilisation, Implantation and Menstruation – Difference
| Process | Meaning | Location |
|---|---|---|
| Fertilisation | Fusion of sperm and ovum | Usually fallopian tube |
| Implantation | Attachment of embryo to uterine lining | Uterus |
| Menstruation | Shedding of uterine lining when pregnancy has not been established | Uterus / reproductive tract |
12. Early Embryonic Development | प्रारंभिक भ्रूणीय विकास
The zygote undergoes mitotic cell divisions called cleavage. The number of cells increases while the early embryo moves towards the uterus.
The cells then undergo differentiation and organise into tissues and organs. Development continues throughout pregnancy.
🧠 Memory Trick:
F → Z → D → E → I → P
F = Fertilisation
Z = Zygote
D = Division
E = Embryo
I = Implantation
P = Pregnancy
F → Z → D → E → I → P
F = Fertilisation
Z = Zygote
D = Division
E = Embryo
I = Implantation
P = Pregnancy
13. Important Developmental Terms
| Term | Meaning |
|---|---|
| Gamete | Haploid reproductive cell |
| Fertilisation | Fusion of male and female gametes |
| Zygote | First diploid cell formed after fertilisation |
| Embryo | Developing organism during early developmental stage |
| Implantation | Attachment of embryo to uterine lining |
| Foetus | Developing baby at a later stage of pregnancy |
| Placenta | Organ for exchange between mother and developing foetus |
| Pregnancy | Period of development of the embryo/foetus in the uterus |
14. 30 MCQs | Multiple Choice Questions
Question 1. Fertilisation in human beings normally occurs in:
A) Ovary
B) Fallopian tube
C) Uterus
D) Vagina
Answer: B) Fallopian tube
Question 2. Fusion of sperm and ovum produces:
A) Embryo
B) Foetus
C) Zygote
D) Placenta
Answer: C) Zygote
Question 3. A normal human sperm contains:
A) 23 chromosomes
B) 46 chromosomes
C) 44 chromosomes
D) 92 chromosomes
Answer: A) 23 chromosomes
Question 4. Implantation occurs in the:
A) Ovary
B) Fallopian tube
C) Uterus
D) Cervix
Answer: C) Uterus
Question 5. The uterine lining is called:
A) Myometrium
B) Endometrium
C) Perimetrium
D) Epididymis
Answer: B) Endometrium
Question 6. The chromosome number of a human ovum is:
A) 46
B) 92
C) 23
D) 44
Answer: C) 23
Question 7. The zygote is:
A) Haploid
B) Diploid
C) Triploid
D) Tetraploid
Answer: B) Diploid
Question 8. Which structure provides exchange of materials between mother and foetus?
A) Placenta
B) Ovary
C) Cervix
D) Urethra
Answer: A) Placenta
Question 9. Which hormone helps maintain the uterine lining?
A) Insulin
B) Progesterone
C) Adrenaline
D) Thyroxine
Answer: B) Progesterone
Question 10. The first cell formed after fertilisation is:
A) Ovum
B) Sperm
C) Embryo
D) Zygote
Answer: D) Zygote
Question 11. Which event directly follows fertilisation?
A) Formation of zygote
B) Menopause
C) Menstruation
D) Ovulation
Answer: A) Formation of zygote
Question 12. The embryo becomes attached to:
A) Ovary
B) Endometrium
C) Epididymis
D) Testis
Answer: B) Endometrium
Question 13. Which process restores the diploid chromosome number?
A) Ovulation
B) Menstruation
C) Fertilisation
D) Implantation
Answer: C) Fertilisation
Question 14. The female gamete is:
A) Sperm
B) Ovum
C) Zygote
D) Embryo
Answer: B) Ovum
Question 15. Which structure connects the ovary to the uterus and is normally the site of fertilisation?
A) Fallopian tube
B) Cervix
C) Vagina
D) Urethra
Answer: A) Fallopian tube
Question 16. If fertilisation does not occur, the uterine lining generally:
A) Remains unchanged permanently
B) Becomes bone
C) Is shed
D) Produces sperm
Answer: C) Is shed
Question 17. The placenta mainly helps in:
A) Producing sperm
B) Exchange of substances
C) Digesting food
D) Producing urine
Answer: B) Exchange of substances
Question 18. Which is haploid?
A) Zygote
B) Body cell
C) Sperm
D) Embryo
Answer: C) Sperm
Question 19. The normal chromosome number in a human zygote is:
A) 23
B) 44
C) 46
D) 92
Answer: C) 46
Question 20. The process of attachment of embryo to the uterine wall is:
A) Fertilisation
B) Implantation
C) Ovulation
D) Menstruation
Answer: B) Implantation
Question 21. hCG is commonly associated with:
A) Pregnancy
B) Digestion
C) Respiration
D) Blood clotting
Answer: A) Pregnancy
Question 22. The developing embryo receives nutrients through the:
A) Placenta
B) Epididymis
C) Prostate
D) Ovary
Answer: A) Placenta
Question 23. Which sequence is correct?
A) Embryo → Zygote → Fertilisation → Implantation
B) Fertilisation → Zygote → Cell division → Embryo → Implantation
C) Implantation → Fertilisation → Zygote → Embryo
D) Zygote → Fertilisation → Ovulation → Embryo
Answer: B) Fertilisation → Zygote → Cell division → Embryo → Implantation
Question 24. Which organ contains the developing embryo after implantation?
A) Ovary
B) Uterus
C) Kidney
D) Testis
Answer: B) Uterus
Question 25. A sperm and an ovum are:
A) Diploid cells
B) Haploid cells
C) Triploid cells
D) Somatic tissues
Answer: B) Haploid cells
Question 26. Which hormone is produced by the corpus luteum and helps maintain the uterine lining?
A) Progesterone
B) Insulin
C) Adrenaline
D) Growth hormone
Answer: A) Progesterone
Question 27. Which one is NOT a result of fertilisation?
A) Formation of zygote
B) Restoration of diploid chromosome number
C) Fusion of gametes
D) Immediate implantation in the ovary
Answer: D) Immediate implantation in the ovary
Question 28. Which substance generally moves from foetus to mother through the placenta?
A) Oxygen
B) Carbon dioxide
C) Glucose
D) Amino acids
Answer: B) Carbon dioxide
Question 29. The embryo is formed from:
A) Zygote
B) Sperm alone
C) Ovum alone
D) Placenta alone
Answer: A) Zygote
Question 30. Which statement is correct?
A) Fertilisation normally occurs in the uterus.
B) Implantation normally occurs in the ovary.
C) Fertilisation forms a zygote.
D) Sperm contains 46 chromosomes.
Answer: C) Fertilisation forms a zygote.
15. 30 Subjective Questions with Answers
2 Marks
Question 1. What is fertilisation? Where does it normally occur in humans?
Answer: Fertilisation is the fusion of male and female gametes to form a zygote. In humans, it normally occurs in the fallopian tube.
2 Marks
Question 2. Define implantation.
Answer: Implantation is the attachment of the developing embryo to the thickened lining of the uterus.
2 Marks
Question 3. What is a zygote?
Answer: A zygote is the diploid cell formed by the fusion of sperm and ovum during fertilisation.
2 Marks
Question 4. How many chromosomes are present in a human sperm and ovum?
Answer: Both sperm and ovum contain 23 chromosomes.
2 Marks
Question 5. What is the role of the placenta?
Answer: Placenta provides a surface for exchange of oxygen, nutrients and wastes between mother and developing foetus.
3 Marks
Question 6. Differentiate between fertilisation and implantation.
Answer:
1. Fertilisation is fusion of sperm and ovum; implantation is attachment of embryo to uterine lining.
2. Fertilisation normally occurs in fallopian tube; implantation occurs in uterus.
3. Fertilisation forms zygote; implantation establishes the embryo in the uterus.
1. Fertilisation is fusion of sperm and ovum; implantation is attachment of embryo to uterine lining.
2. Fertilisation normally occurs in fallopian tube; implantation occurs in uterus.
3. Fertilisation forms zygote; implantation establishes the embryo in the uterus.
3 Marks
Question 7. Explain the formation of a zygote.
Answer: During fertilisation, a sperm fuses with an ovum. Their nuclei combine and form a diploid cell called the zygote. It contains 46 chromosomes in humans.
3 Marks
Question 8. Explain the early development of the zygote.
Answer: The zygote undergoes repeated mitotic cell divisions. The number of cells increases, forming an embryo. The developing embryo moves towards the uterus and later undergoes implantation.
3 Marks
Question 9. Why are gametes haploid?
Answer: Gametes contain half the chromosome number so that fusion of male and female gametes restores the normal diploid chromosome number in the zygote.
3 Marks
Question 10. What happens to the uterine lining when fertilisation does not occur?
Answer: Hormone levels fall, the thickened uterine lining breaks down and is shed from the body as menstruation.
4 Marks
Question 11. Explain the sequence from fertilisation to implantation.
Answer:
1. Sperm fuses with ovum.
2. A diploid zygote is formed.
3. Zygote undergoes repeated cell division.
4. It develops into an embryo and attaches to the uterine lining during implantation.
1. Sperm fuses with ovum.
2. A diploid zygote is formed.
3. Zygote undergoes repeated cell division.
4. It develops into an embryo and attaches to the uterine lining during implantation.
4 Marks
Question 12. Describe the importance of the placenta.
Answer:
1. Provides a large exchange surface.
2. Supplies oxygen and nutrients to the foetus.
3. Helps transfer carbon dioxide and metabolic wastes towards the mother's circulation.
4. Also functions as an endocrine tissue during pregnancy.
1. Provides a large exchange surface.
2. Supplies oxygen and nutrients to the foetus.
3. Helps transfer carbon dioxide and metabolic wastes towards the mother's circulation.
4. Also functions as an endocrine tissue during pregnancy.
4 Marks
Question 13. Distinguish between zygote, embryo and foetus.
Answer:
Zygote: First diploid cell formed after fertilisation.
Embryo: Early developing organism formed after repeated cell division and differentiation.
Foetus: Developing baby at a later stage of pregnancy when body structures become more recognisable.
Zygote: First diploid cell formed after fertilisation.
Embryo: Early developing organism formed after repeated cell division and differentiation.
Foetus: Developing baby at a later stage of pregnancy when body structures become more recognisable.
4 Marks
Question 14. Explain why fertilisation restores the chromosome number.
Answer: Sperm contains 23 chromosomes and ovum contains 23 chromosomes. Their fusion combines these sets, producing a zygote with 46 chromosomes. Thus the diploid chromosome number is restored.
4 Marks
Question 15. Explain the role of progesterone during the reproductive cycle and pregnancy.
Answer: Progesterone is produced mainly by the corpus luteum after ovulation. It helps maintain the uterine lining. During pregnancy, hormonal support maintains conditions suitable for continued development.
5 Marks
Question 16. Explain fertilisation in human beings in detail.
Answer:
1. Ovulation releases an ovum from an ovary.
2. Sperm travel through the female reproductive tract.
3. A sperm may reach the fallopian tube.
4. Fusion of sperm and ovum forms a zygote.
5. The zygote begins cell division and develops into an embryo.
1. Ovulation releases an ovum from an ovary.
2. Sperm travel through the female reproductive tract.
3. A sperm may reach the fallopian tube.
4. Fusion of sperm and ovum forms a zygote.
5. The zygote begins cell division and develops into an embryo.
5 Marks
Question 17. Explain implantation and its importance.
Answer: Implantation is attachment of the developing embryo to the endometrium. It is important because the uterus provides a suitable environment and the placenta develops to support exchange of materials between mother and foetus.
5 Marks
Question 18. Explain the role of placenta in pregnancy.
Answer:
• Provides oxygen to foetus.
• Supplies nutrients.
• Receives carbon dioxide and metabolic wastes from foetus.
• Provides an exchange surface.
• Produces hormones important for pregnancy.
• Provides oxygen to foetus.
• Supplies nutrients.
• Receives carbon dioxide and metabolic wastes from foetus.
• Provides an exchange surface.
• Produces hormones important for pregnancy.
5 Marks
Question 19. Describe what happens after fertilisation.
Answer: A zygote forms and undergoes repeated mitotic divisions. It develops into an embryo, travels towards the uterus and implants in the endometrium. The placenta develops and the embryo continues to grow and differentiate.
5 Marks
Question 20. Why is direct mixing of maternal and foetal blood normally avoided?
Answer: The placental interface allows exchange of oxygen, nutrients and wastes without requiring direct mixing of maternal and foetal blood. This provides a controlled exchange environment.
6 Marks
Question 21. Describe the complete sequence from ovulation to implantation.
Answer:
1. An ovum is released from the ovary during ovulation.
2. The ovum enters the fallopian tube.
3. Sperm may reach the fallopian tube.
4. Fusion of sperm and ovum forms a zygote.
5. The zygote undergoes repeated cell division.
6. The developing embryo reaches the uterus and implants in the endometrium.
1. An ovum is released from the ovary during ovulation.
2. The ovum enters the fallopian tube.
3. Sperm may reach the fallopian tube.
4. Fusion of sperm and ovum forms a zygote.
5. The zygote undergoes repeated cell division.
6. The developing embryo reaches the uterus and implants in the endometrium.
6 Marks
Question 22. Explain the development of the zygote into an embryo.
Answer: The zygote undergoes repeated mitotic divisions. The number of cells increases and the cells begin to differentiate. The developing cell mass forms an early embryo. It moves towards the uterus and becomes implanted in the uterine lining. Further cell division, differentiation and organ formation continue.
6 Marks
Question 23. Explain how the placenta supports the developing foetus.
Answer:
1. It provides a large exchange surface.
2. Oxygen moves from maternal blood towards foetal blood.
3. Nutrients are supplied to the foetus.
4. Carbon dioxide moves from foetus towards mother.
5. Some metabolic wastes are transferred towards maternal circulation.
6. Placenta also produces hormones that support pregnancy.
1. It provides a large exchange surface.
2. Oxygen moves from maternal blood towards foetal blood.
3. Nutrients are supplied to the foetus.
4. Carbon dioxide moves from foetus towards mother.
5. Some metabolic wastes are transferred towards maternal circulation.
6. Placenta also produces hormones that support pregnancy.
6 Marks
Question 24. Explain the significance of fertilisation in sexual reproduction.
Answer:
• It brings male and female genetic material together.
• It forms the zygote.
• It restores diploid chromosome number.
• It initiates development of a new organism.
• It contributes to genetic variation because genetic material comes from two parents.
• It begins embryonic development.
• It brings male and female genetic material together.
• It forms the zygote.
• It restores diploid chromosome number.
• It initiates development of a new organism.
• It contributes to genetic variation because genetic material comes from two parents.
• It begins embryonic development.
6 Marks
Question 25. Explain the difference between fertilisation, implantation and pregnancy.
Answer:
Fertilisation: Fusion of sperm and ovum to form zygote; normally in fallopian tube.
Implantation: Attachment of embryo to endometrium; in uterus.
Pregnancy: Period during which the developing embryo/foetus grows in the uterus.
Fertilisation: Fusion of sperm and ovum to form zygote; normally in fallopian tube.
Implantation: Attachment of embryo to endometrium; in uterus.
Pregnancy: Period during which the developing embryo/foetus grows in the uterus.
6 Marks
Question 26. Explain the hormonal importance of progesterone and hCG during early pregnancy.
Answer: Progesterone helps maintain the uterine lining. In early pregnancy, hCG supports the corpus luteum so that progesterone production can continue. This helps maintain the conditions required for the developing embryo.
6 Marks
Question 27. A sperm contains 23 chromosomes and the ovum contains 23 chromosomes. Explain what happens after their fusion.
Answer: The sperm and ovum fuse during fertilisation. Their chromosome sets combine, producing a zygote with 46 chromosomes. The zygote undergoes mitotic divisions and develops into an embryo. The embryo later implants in the uterus.
6 Marks
Question 28. Explain why implantation is necessary for successful pregnancy.
Answer: Implantation establishes the embryo in the uterus. The uterine lining provides support and blood supply, while the developing placenta facilitates exchange of oxygen, nutrients and wastes. Therefore, implantation is essential for continued embryonic development.
6 Marks
Question 29. Explain the changes that occur when fertilisation does not take place.
Answer:
1. The ovum is not fertilised.
2. The corpus luteum eventually degenerates.
3. Progesterone and other ovarian hormone levels fall.
4. The uterine lining is no longer maintained in the same way.
5. The lining breaks down.
6. Menstruation occurs.
1. The ovum is not fertilised.
2. The corpus luteum eventually degenerates.
3. Progesterone and other ovarian hormone levels fall.
4. The uterine lining is no longer maintained in the same way.
5. The lining breaks down.
6. Menstruation occurs.
6 Marks
Question 30. Write a detailed account of human fertilisation, implantation and pregnancy.
Answer: During ovulation an ovum is released into the fallopian tube. Sperm may reach the ovum and one sperm can fuse with it, forming a diploid zygote. The zygote undergoes repeated cell division and forms an embryo. The embryo moves into the uterus and attaches to the endometrium through implantation. A placenta develops and facilitates exchange of oxygen, nutrients and wastes between mother and foetus. The embryo continues to grow, differentiate and develop into a foetus during pregnancy.
16. HOTS / Competency-Based Questions
HOTS 1. Why does fertilisation not normally occur in the uterus?
Answer: The fallopian tube provides the usual location where sperm and ovum meet. The uterus mainly provides the environment for implantation and subsequent development.
Answer: The fallopian tube provides the usual location where sperm and ovum meet. The uterus mainly provides the environment for implantation and subsequent development.
HOTS 2. If both sperm and ovum had 46 chromosomes, what problem would arise?
Answer: Their fusion would produce a zygote with 92 chromosomes rather than the normal diploid number of 46. Therefore, meiosis must reduce chromosome number in gametes.
Answer: Their fusion would produce a zygote with 92 chromosomes rather than the normal diploid number of 46. Therefore, meiosis must reduce chromosome number in gametes.
HOTS 3. Why is a thick uterine lining important after implantation?
Answer: It provides a suitable, well-supplied environment for the developing embryo and supports formation and functioning of the placenta.
Answer: It provides a suitable, well-supplied environment for the developing embryo and supports formation and functioning of the placenta.
HOTS 4. Why is the placenta described as an exchange organ?
Answer: It allows oxygen and nutrients to reach the foetus and carbon dioxide and certain wastes to move towards the mother's circulation.
Answer: It allows oxygen and nutrients to reach the foetus and carbon dioxide and certain wastes to move towards the mother's circulation.
HOTS 5. A pregnancy test detects hCG. Why can this hormone be used as an indicator of pregnancy?
Answer: hCG is produced during early pregnancy and supports the corpus luteum. Its presence in urine or blood can therefore indicate pregnancy.
Answer: hCG is produced during early pregnancy and supports the corpus luteum. Its presence in urine or blood can therefore indicate pregnancy.
17. Assertion–Reason Practice
Question 1.
Assertion (A): Fertilisation restores the diploid chromosome number.
Reason (R): Human sperm and ovum are haploid.
Assertion (A): Fertilisation restores the diploid chromosome number.
Reason (R): Human sperm and ovum are haploid.
Answer: Both A and R are true, and R correctly explains A.
Question 2.
Assertion (A): Implantation occurs in the fallopian tube.
Reason (R): Fertilisation normally occurs in the fallopian tube.
Assertion (A): Implantation occurs in the fallopian tube.
Reason (R): Fertilisation normally occurs in the fallopian tube.
Answer: A is false, but R is true.
Question 3.
Assertion (A): Placenta helps in exchange of substances.
Reason (R): The foetus requires oxygen and nutrients for growth.
Assertion (A): Placenta helps in exchange of substances.
Reason (R): The foetus requires oxygen and nutrients for growth.
Answer: Both A and R are true, and R supports A.
18. Important Diagram Labelling
Important Labels: Ovary, Fallopian Tube, Uterus, Endometrium, Cervix, Vagina.
19. CBSE Golden Points | परीक्षा के लिए महत्वपूर्ण बिंदु
✔ Fertilisation = fusion of sperm and ovum.
✔ Fertilisation normally occurs in the fallopian tube.
✔ Zygote is diploid.
✔ Human sperm = 23 chromosomes.
✔ Human ovum = 23 chromosomes.
✔ Human zygote = 46 chromosomes.
✔ Implantation occurs in the uterus.
✔ Implantation means attachment of embryo to endometrium.
✔ Placenta provides exchange of oxygen, nutrients and wastes.
✔ Progesterone helps maintain the uterine lining.
✔ hCG is associated with early pregnancy and is detected by pregnancy tests.
✔ If fertilisation does not occur, the uterine lining is shed during menstruation.
✔ Fertilisation normally occurs in the fallopian tube.
✔ Zygote is diploid.
✔ Human sperm = 23 chromosomes.
✔ Human ovum = 23 chromosomes.
✔ Human zygote = 46 chromosomes.
✔ Implantation occurs in the uterus.
✔ Implantation means attachment of embryo to endometrium.
✔ Placenta provides exchange of oxygen, nutrients and wastes.
✔ Progesterone helps maintain the uterine lining.
✔ hCG is associated with early pregnancy and is detected by pregnancy tests.
✔ If fertilisation does not occur, the uterine lining is shed during menstruation.
20. One-Line Revision
Ovulation → Fertilisation → Zygote → Cell Division → Embryo → Implantation → Placenta → Foetus → Pregnancy
अंडोत्सर्जन → निषेचन → युग्मनज → कोशिका विभाजन → भ्रूण → आरोपण → प्लेसेंटा → भ्रूणीय विकास → गर्भावस्था
अंडोत्सर्जन → निषेचन → युग्मनज → कोशिका विभाजन → भ्रूण → आरोपण → प्लेसेंटा → भ्रूणीय विकास → गर्भावस्था
21. Quick Summary | त्वरित पुनरावृत्ति
Fertilisation: Sperm + Ovum → Zygote
Site: Fallopian tube
Implantation: Embryo attaches to endometrium
Site of implantation: Uterus
Placenta: Exchange of materials between mother and developing foetus
Progesterone: Helps maintain uterine lining
hCG: Important early pregnancy hormone and pregnancy-test marker
Without fertilisation: Uterine lining sheds → Menstruation
Site: Fallopian tube
Implantation: Embryo attaches to endometrium
Site of implantation: Uterus
Placenta: Exchange of materials between mother and developing foetus
Progesterone: Helps maintain uterine lining
hCG: Important early pregnancy hormone and pregnancy-test marker
Without fertilisation: Uterine lining sheds → Menstruation
Class 10 Science | How Do Organisms Reproduce?
Fertilisation • Implantation • Pregnancy • Placenta
CBSE + Foundation + Competitive Preparation
Fertilisation • Implantation • Pregnancy • Placenta
CBSE + Foundation + Competitive Preparation
