Introduction
Fertilization (निषेचन) is the biological process in which a male gamete (sperm) fuses with a female gamete (ovum/egg) to form a zygote. According to NCERT, fertilization is an essential step in human reproduction because it marks the beginning of the development of a new individual.
Definition: Fertilization is the fusion of the nucleus of a sperm and the nucleus of an ovum to form a zygote.
Human Reproductive Cells (Gametes)
| Gamete | Produced By | Function |
|---|---|---|
| Sperm | Testes (Male) | Carries male genetic material |
| Ovum (Egg) | Ovaries (Female) | Carries female genetic material |
Important Facts
- A sperm is the male reproductive cell.
- An ovum (egg) is the female reproductive cell.
- Both gametes contain half the genetic material needed for a new individual.
- Fertilization restores the complete set of chromosomes.
Where Does Fertilization Occur in Humans?
In humans, fertilization usually takes place in the fallopian tube (oviduct).
Sequence of Events
- Ovary releases a mature egg (ovulation).
- Egg enters the fallopian tube.
- Millions of sperms travel through the female reproductive tract.
- One sperm successfully reaches and penetrates the egg.
- The nuclei of sperm and egg fuse.
- A zygote is formed.
Process of Fertilization in Humans
Step 1: Ovulation
- A mature ovum is released from one of the ovaries.
- This process is called ovulation.
Step 2: Sperm Transfer
- Sperms enter the female reproductive tract.
- They swim towards the fallopian tube.
Step 3: Fusion of Gametes
- One sperm penetrates the ovum.
- The nuclei of both cells fuse together.
Step 4: Formation of Zygote
- A single cell called zygote is formed.
- The zygote contains genetic information from both parents.
Step 5: Beginning of Development
- The zygote undergoes repeated cell divisions.
- It develops into an embryo.
What is a Zygote?
A zygote is the first cell formed after fertilization.
Characteristics of a Zygote
- Single-celled structure.
- Contains chromosomes from both parents.
- Marks the beginning of a new life.
- Undergoes rapid cell division.
Formula
Sperm + Ovum → Zygote
Importance of Fertilization
1. Formation of a New Individual
- Starts the development of a baby.
2. Restoration of Chromosome Number
- Combines genetic material from both parents.
3. Transfer of Hereditary Traits
- Characteristics are passed from parents to offspring.
4. Initiates Embryonic Development
- Leads to embryo formation and growth.
Fertilization vs Zygote vs Embryo
| Feature | Fertilization | Zygote | Embryo |
|---|---|---|---|
| Meaning | Fusion of sperm and ovum | First cell formed | Developing baby after cell divisions |
| Stage | Process | Single cell | Multicellular stage |
| Result | Formation of zygote | Begins division | Develops organs |
Internal Fertilization in Humans
Humans show internal fertilization.
Internal Fertilization Means
- Fusion of gametes occurs inside the female body.
- Provides better protection to the developing embryo.
- Increases chances of successful reproduction.
Examples of Internal Fertilization
- Humans
- Dogs
- Cats
- Cows
- Birds
Fertilization and Heredity
During fertilization:
- The sperm contributes genetic information from the father.
- The ovum contributes genetic information from the mother.
- The zygote receives characteristics from both parents.
This is why children resemble both their mother and father.
Key NCERT Points to Remember
✅ Fertilization is the fusion of sperm and ovum.
✅ It occurs in the fallopian tube of the female reproductive system.
✅ Fertilization forms a zygote.
✅ The zygote develops into an embryo.
✅ Humans exhibit internal fertilization.
✅ Fertilization combines genetic material from both parents.
Practice Questions with Answers
Q1. What is fertilization?
Answer: Fertilization is the fusion of a sperm and an ovum to form a zygote.
Q2. Where does fertilization occur in humans?
Answer: Fertilization usually occurs in the fallopian tube (oviduct).
Q3. What is formed after fertilization?
Answer: A zygote is formed after fertilization.
Q4. What are gametes?
Answer: Gametes are reproductive cells such as sperm and ovum.
Q5. Why is fertilization important?
Answer: It initiates the development of a new individual and combines genetic material from both parents.
Fill in the Blanks
- Fertilization is the fusion of __________ and __________.Answer: sperm, ovum
- Fertilization in humans occurs in the __________.Answer: fallopian tube
- The cell formed after fertilization is called a __________.Answer: zygote
- Humans show __________ fertilization.Answer: internal
- The female gamete is called an __________.Answer: ovum
- The male gamete is called a __________.Answer: sperm
- The zygote develops into an __________.Answer: embryo
- Fertilization combines genetic material from __________ parents.Answer: both
- Ovulation occurs in the __________.Answer: ovary
- Fertilization marks the beginning of a new __________.
Answer: life
MCQs (Multiple Choice Questions)
1. What is fertilization?
A. Cell division
B. Fusion of sperm and ovum
C. Growth of embryo
D. Ovulation
✅ Answer: B
2. Fertilization in humans usually occurs in the:
A. Uterus
B. Ovary
C. Fallopian tube
D. Vagina
✅ Answer: C
3. Which cell is formed after fertilization?
A. Embryo
B. Foetus
C. Zygote
D. Ovary
✅ Answer: C
4. The male reproductive cell is called:
A. Ovum
B. Egg
C. Zygote
D. Sperm
✅ Answer: D
5. The female reproductive cell is:
A. Sperm
B. Ovum
C. Embryo
D. Foetus
✅ Answer: B
6. Humans exhibit:
A. External fertilization
B. Internal fertilization
C. Both
D. None
✅ Answer: B
7. Fertilization results in the formation of:
A. Ovum
B. Sperm
C. Zygote
D. Placenta
✅ Answer: C
8. The zygote develops into:
A. Ovary
B. Embryo
C. Egg
D. Sperm
✅ Answer: B
9. Which organ releases the ovum?
A. Uterus
B. Testis
C. Ovary
D. Kidney
✅ Answer: C
10. Fertilization combines genetic material from:
A. Father only
B. Mother only
C. Both parents
D. Neither parent
✅ Answer: C
Quick Revision
- Fertilization = Fusion of sperm and ovum.
- Occurs in the fallopian tube.
- Produces a zygote.
- Zygote develops into an embryo.
- Humans show internal fertilization.
- Genetic information comes from both parents.
- Fertilization is the first step in the development of a new human being.
