Lesson 8: How Do Organisms Reproduce? (NCERT Science – Class 10)

🖊️ Kishur Boruah, Teacher 

Dear learners, Welcome to Jnaanangkur The Learning Hub. Life on Earth is a continuous cycle, and one of its most incredible processes is reproduction—the way living beings create new life. Imagine a world where no organism could reproduce; species would disappear, and life as we know it would come to an end!

In this chapter, we explore the different ways organisms reproduce, from the simple binary fission in bacteria to the complex reproductive systems in humans. You'll learn how a tiny seed transforms into a huge tree and how genetic variations help species evolve and survive.

At Jnaanangkur The Learning Hub, we believe that learning about life’s processes makes science more exciting and relatable. So, let’s dive into this fascinating topic and uncover the secrets of how life continues from one generation to the next!

Lesson 8: How Do Organisms Reproduce? (NCERT Science – Class 10)

Modes of Reproduction

Organisms reproduce in two main ways: Asexual Reproduction and Sexual Reproduction.

1. Asexual Reproduction

Asexual reproduction involves a single parent and produces offspring that are genetically identical to the parent. This type of reproduction is common in unicellular organisms, some plants, and lower animals.

Types of Asexual Reproduction:

∆ Binary Fission: Seen in bacteria and amoeba, where one cell divides into two identical cells.

∆ Multiple Fission: Seen in Plasmodium (malaria-causing parasite), where a single organism divides into many at once.

∆ Fragmentation: Seen in organisms like Spirogyra (a type of algae), where a body breaks into pieces, and each piece grows into a new organism.

∆ Budding: Seen in Hydra and yeast, where a small bud grows on the parent’s body and eventually detaches to form a new organism.

∆ Vegetative Propagation: Seen in plants like potatoes and money plants, where new plants grow from stems, roots, or leaves.

∆ Spore Formation: Seen in fungi like bread mold, where tiny spores spread and grow into new organisms under favorable conditions.

2. Sexual Reproduction

Sexual reproduction involves two parents and the fusion of male and female gametes (sex cells). It results in genetic variation, which helps in evolution.

Sexual Reproduction in Plants

Flowers are the reproductive organs of plants.

The male part (stamen) produces pollen grains, while the female part (carpel) contains the ovary, where ovules develop.

Pollination is the process of pollen transfer from the stamen to the carpel, which can be done by wind, water, or insects.

Fertilization occurs when pollen meets the ovule, leading to seed formation.

The seed grows into a new plant under suitable conditions (germination).

Sexual Reproduction in Humans

The human reproductive system is more complex and involves the production of gametes (sperm and egg) and their fusion to form a new life.

Male Reproductive System:

Testes: Produce sperm and the hormone testosterone.

Vas Deferens: A tube that carries sperm.

Urethra: A common passage for urine and sperm.

Penis: Organ for sperm transfer.

Female Reproductive System:

Ovaries: Produce eggs and hormones (estrogen and progesterone).

Fallopian Tubes: Site of fertilization where sperm meets the egg.

Uterus: Where the fertilized egg develops into a baby.

Vagina: The birth canal.

Fertilization and Development

Fertilization occurs in the fallopian tube when a sperm cell fuses with an egg.

The fertilized egg (zygote) divides and implants in the uterus.

Over nine months, the baby develops in the mother’s womb.

Reproductive Health

Reproductive health is essential for the well-being of individuals. Important aspects include:

Birth control methods: Contraceptives help in family planning.

Sexually Transmitted Diseases (STDs): Diseases like HIV/AIDS, syphilis, and gonorrhea spread through unsafe sexual practices.

Menstrual Cycle: The monthly cycle in females where the uterus prepares for pregnancy.

Dear learners, In this article we discussed only most important points of the lesson. Please read your textbook for more information.

Key points of the lesson :

How Do Organisms Reproduce

* Reproduction is as important as other life processes for the smooth survival of an organism.

* Reproduction involves the replication of DNA and the production of other cell organelles in the cell.

* Different organisms reproduce in different ways depending on their body structure.

* In the process of bifurcation, most bacteria and food organisms very commonly divide the cell to form two or more daughter cells.

* Creatures like hydras can revive from fragments even if their bodies are fragmented. They can even create buds in the body and become perfect from them.

* Some plants form new plants through organic propagation from roots, stems and leaves.

* These organisms are asexual reproducers that can produce new generations directly from an individual in alone.

* Sexual reproduction involves two separate individuals to produce a new generation.

* Heterogeneity occurs in the process of DNA replication and is essential for the survival of a species. Such disparities are most common in sexual reproduction.

* Pollination is the process by which pollen moves from the pollen grain to the embryo in sexual reproduction of flowering plants. 

* Fertilization occurs in the next stage.

* During adolescence, a girl's breasts increase in size, and a boy's beard grows on his face. Such changes are signs of sexual maturity.

* The human reproductive system consists of the sperm-producing glands, testes, fallopian tubes, testes, prostate gland, urethra and penis.

* The human female reproductive system is made up of the ovaries, fallopian tubes, uterus and vagina.

* In human sexual reproduction, male sperm are implanted in the vagina of the female body.

* Condoms, oral contraceptive pills, copper-T and some other methods are used to prevent pregnancy.

Lesson 8: How Do Organisms Reproduce? – Important Questions and Answers

Q. What is reproduction?

Answer : Reproduction is the biological process by which organisms produce new individuals of their species.

Q. Name two organisms that reproduce by binary fission.

Answer: Amoeba and Bacteria.

Q: What is the male reproductive organ in a flower?

Answer: The stamen (comprising anther and filament).

Q: Which part of the female reproductive system is the site of fertilization in humans?

Answer: The Fallopian tube.

Q: What are the two types of reproduction?

Answer: Asexual reproduction and Sexual reproduction.

Q: What is vegetative propagation? Give two examples.

Answer: Vegetative propagation is a type of asexual reproduction in plants where new plants grow from stems, roots, or leaves.

Examples:

1. Potato (grows from underground stem tubers)

2. Money plant (grows from stem cuttings)

Q: How does budding occur in Hydra?

Answer: In Hydra, a small bud develops on the parent’s body. This bud gradually grows, develops tentacles, and eventually detaches to become an independent organism.

Q: What is the role of the uterus in human reproduction?

Answer: The uterus provides a protective environment for the developing embryo and supplies it with nutrients through the placenta.

Q: What is pollination? Name its two types.

Answer: Pollination is the transfer of pollen from the anther to the stigma of a flower.

Types:

1. Self-pollination: Pollen transfers within the same flower or plant.

2. Cross-pollination: Pollen transfers from one flower to another flower of the same species.

Q: What are sexually transmitted diseases (STDs)? Name two examples.

Answer: STDs are infections spread through sexual contact.

Examples:

1. HIV/AIDS

2. Syphilis

Q: Explain the process of sexual reproduction in flowering plants.

Answer:

1. Pollination: The transfer of pollen from the male part (anther) to the female part (stigma).

2. Fertilization: Pollen reaches the ovary, where it fuses with the ovule to form a zygote.

3. Seed Formation: The fertilized ovule develops into a seed, and the ovary becomes a fruit.

4. Germination: Under suitable conditions, the seed grows into a new plant.

Q: Describe the structure and function of the male reproductive system in humans.

Answer: The male reproductive system consists of:

1. Testes: Produce sperm and testosterone.

2. Vas Deferens: Carries sperm from testes to urethra.

3. Urethra: Common passage for sperm and urine.

4. Penis: Transfers sperm to the female reproductive system.

Function: Produces and delivers sperm for fertilization.

Q: Explain the menstrual cycle in females.

Answer:

The menstrual cycle is a 28-day cycle in which the uterus prepares for pregnancy.

If no fertilization occurs, the thickened uterus lining breaks down and is released as menstrual bleeding (period).

Key phases:

1. Menstrual Phase (Day 1-5): Shedding of uterus lining.

2. Follicular Phase (Day 6-14): Egg matures in the ovary.

3. Ovulation (Day 14): The mature egg is released.

4. Luteal Phase (Day 15-28): Uterus prepares for pregnancy.

Q: How does the human embryo develop after fertilization?

Answer:

1. Fertilization occurs in the fallopian tube.

2. The fertilized egg (zygote) undergoes multiple cell divisions.

3. It travels to the uterus and implants in the uterine wall.

4. Over nine months, it develops into a fetus, nourished by the placenta.

5. After full development, the baby is delivered.

Q: Why is variation important in sexual reproduction?

Answer: Variation occurs due to genetic mixing in sexual reproduction. It helps species adapt to changing environments and increases survival chances.

Q: Why do organisms that reproduce asexually show less variation?

Answer: Asexual reproduction produces identical copies of the parent (clones), so there is no mixing of genes, leading to less variation.

Q: Why is DNA copying important in reproduction?

Answer: DNA copying ensures that genetic information is passed from parents to offspring, maintaining species continuity. However, slight errors (mutations) can lead to variations.

NCERT Class 10 Science – Chapter 8: 

How Do Organisms Reproduce?

Q. What is the importance of DNA copying in reproduction?

Answer:

DNA copying (replication) is essential in reproduction because:

1. It ensures the transmission of genetic information from one generation to the next.

2. It allows the formation of offspring with characteristics similar to their parents.

3. It introduces variations due to small errors (mutations) during copying, which helps in evolution and adaptation.

Q. Why is variation beneficial to the species but not necessarily for the individual?

Answer:

Variation is beneficial to a species because:

It helps species adapt to changing environmental conditions.

It increases the chances of survival in case of sudden climate change or disease outbreaks.

It contributes to evolution over generations.

For an individual, variation may or may not be beneficial. For example, a mutation may result in a disadvantageous trait, reducing survival chances.

Q.  How will an organism be benefited if it reproduces through spores?

Answer:

Spore formation is beneficial because:

Spores are lightweight and can spread easily through air, water, or other means.

They can survive harsh conditions like extreme temperatures and drought.

Large numbers of spores are produced, increasing the chances of reproduction.

When conditions become favorable, spores grow into new organisms.

Example: Fungi (like bread mold) reproduce through spores.

Q. Why is vegetative propagation practiced for growing some plants? Give two examples.

Answer:

Vegetative propagation is practiced because:

It allows the rapid growth of plants without seeds.

It produces plants that are genetically identical to the parent (clones).

It helps maintain desired traits in plants, such as fruit quality and resistance to diseases.

Examples:

1. Potato: Grows from underground stem tubers.

2. Rose: Grows from stem cuttings.

Q. What are the different methods of asexual reproduction? Explain any two with examples.

Answer:

The different methods of asexual reproduction are:

1. Binary Fission – One cell divides into two identical cells (Example: Amoeba).

2. Multiple Fission – One cell divides into many daughter cells (Example: Plasmodium).

3. Budding – A small bud forms on the parent body and grows into a new organism (Example: Hydra, Yeast).

4. Fragmentation – The body breaks into pieces, and each piece grows into a new organism (Example: Spirogyra).

5. Vegetative Propagation – New plants grow from stems, roots, or leaves (Example: Money Plant, Potato).

6. Spore Formation – Tiny spores spread and grow into new organisms (Example: Fungi, Bread mold).

Q.  What are the advantages of sexual reproduction over asexual reproduction?

Answer:

Sexual reproduction has several advantages over asexual reproduction, which help in the survival and evolution of species. Some of the key advantages are:

1. Genetic Variation:

In sexual reproduction, offspring inherit genes from both parents.

This creates differences (variations) among individuals, making species better suited for survival in changing environments.

2. Better Adaptation:

Variations help organisms adapt to new environments, increasing their chances of survival.

For example, some organisms may develop resistance to diseases or harsh climates.

3. Prevents Cloning:

In asexual reproduction, all offspring are exact copies (clones) of the parent.

This lack of variation makes the species vulnerable to diseases or environmental changes.

4. Leads to Evolution:

Genetic differences passed on through generations drive evolution.

Over time, beneficial traits are preserved, leading to stronger and more advanced species.

5. Elimination of Harmful Traits:

In sexual reproduction, harmful mutations or weak traits have a chance of being eliminated.

In asexual reproduction, all negative traits are passed on without change.

Q. What are the functions performed by the human reproductive system?

Answer:

The human reproductive system performs the following functions:

Production of Gametes: Males produce sperm, and females produce eggs.

Fertilization: Sperm and egg fuse to form a zygote.

Development of Embryo: The zygote develops into a baby inside the uterus.

Birth and Nourishment: The baby is born and nourished by the mother’s milk.

Hormonal Regulation: Male and female reproductive hormones (testosterone, estrogen, and progesterone) control reproductive functions.

Q.  How does the embryo get nourishment inside the mother’s body?

Answer:

The embryo gets nourishment through the placenta, a special organ that connects the mother’s blood supply to the baby. The placenta:

Transfers oxygen and nutrients from the mother’s blood to the embryo.

Removes waste products from the embryo’s blood.

Helps in hormone production for pregnancy maintenance.

This ensures proper growth and development of the baby inside the uterus.

Q. Why does menstruation occur?

Answer:

Menstruation occurs when fertilization does not take place. The female body prepares for pregnancy every month by thickening the uterus lining. If fertilization does not occur:

The uterus lining breaks down.

It is released through the vagina as blood and tissue (menstrual flow).

This cycle repeats every 28 days.

It is a natural process in females from puberty to menopause.

12. What are the different methods of contraception? How do they work?

Answer:

Contraceptive methods prevent unwanted pregnancy. They include:

1. Barrier Methods:

Condoms and Diaphragms prevent sperm from reaching the egg.

2. Hormonal Methods:

Oral pills prevent ovulation.

Injections/implants release hormones that stop egg release.

3. Intrauterine Devices (IUDs):

Copper-T is placed in the uterus to prevent fertilization.

4. Surgical Methods:

Vasectomy (in males): Cutting of vas deferens to prevent sperm transport.

Tubectomy (in females): Cutting of fallopian tubes to prevent egg movement.

These methods help in birth control and prevent sexually transmitted diseases (STDs).

Q. How are the modes of reproduction different in unicellular and multicellular organisms?

Answer:

Unicellular organisms reproduce mainly by asexual methods, while multicellular organisms use both asexual and sexual reproduction for continuity of life.

Q. What is the importance of DNA copying in reproduction?

Answer:

DNA copying (replication) is essential in reproduction because:

1. It ensures the transmission of genetic information from one generation to the next.

2. It allows the formation of offspring with characteristics similar to their parents.

3. It introduces variations due to small errors (mutations) during copying, which helps in evolution and adaptation.

Q. Why is variation beneficial to the species but not necessarily for the individual?

Answer:

Variation is beneficial to a species because:

It helps species adapt to changing environmental conditions.

It increases the chances of survival in case of sudden climate change or disease outbreaks.

It contributes to evolution over generations.

For an individual, variation may or may not be beneficial. For example, a mutation may result in a disadvantageous trait, reducing survival chances.

Q. How will an organism be benefited if it reproduces through spores?

Answer:

Spore formation is beneficial because:

Spores are lightweight and can spread easily through air, water, or other means.

They can survive harsh conditions like extreme temperatures and drought.

Large numbers of spores are produced, increasing the chances of reproduction.

When conditions become favorable, spores grow into new organisms.

Example: Fungi (like bread mold) reproduce through spores.

Q. Why is vegetative propagation practiced for growing some plants? Give two examples.

Answer:

Vegetative propagation is practiced because:

It allows the rapid growth of plants without seeds.

It produces plants that are genetically identical to the parent (clones).

It helps maintain desired traits in plants, such as fruit quality and resistance to diseases.

Examples:

1. Potato: Grows from underground stem tubers.

2. Rose: Grows from stem cuttings.

Q. What are the different methods of asexual reproduction? Explain any two with examples.

Answer:

The different methods of asexual reproduction are:

1. Binary Fission – One cell divides into two identical cells (Example: Amoeba).

2. Multiple Fission – One cell divides into many daughter cells (Example: Plasmodium).

3. Budding – A small bud forms on the parent body and grows into a new organism (Example: Hydra, Yeast).

4. Fragmentation – The body breaks into pieces, and each piece grows into a new organism (Example: Spirogyra).

5. Vegetative Propagation – New plants grow from stems, roots, or leaves (Example: Money Plant, Potato).

6. Spore Formation – Tiny spores spread and grow into new organisms (Example: Fungi, Bread mold).

Q. What are the advantages of sexual reproduction over asexual reproduction?

Answer:

Sexual reproduction has several advantages over asexual reproduction, which help in the survival and evolution of species. Some of the key advantages are:

1. Genetic Variation:

In sexual reproduction, offspring inherit genes from both parents.

This creates differences (variations) among individuals, making species better suited for survival in changing environments.

2. Better Adaptation:

Variations help organisms adapt to new environments, increasing their chances of survival.

For example, some organisms may develop resistance to diseases or harsh climates.

3. Prevents Cloning:

In asexual reproduction, all offspring are exact copies (clones) of the parent.

This lack of variation makes the species vulnerable to diseases or environmental changes.

4. Leads to Evolution:

Genetic differences passed on through generations drive evolution.

Over time, beneficial traits are preserved, leading to stronger and more advanced species.

5. Elimination of Harmful Traits:

In sexual reproduction, harmful mutations or weak traits have a chance of being eliminated.

In asexual reproduction, all negative traits are passed on without change.

Q. What are the functions performed by the human reproductive system?

Answer:

The human reproductive system performs the following functions:

Production of Gametes: Males produce sperm, and females produce eggs.

Fertilization: Sperm and egg fuse to form a zygote.

Development of Embryo: The zygote develops into a baby inside the uterus.

Birth and Nourishment: The baby is born and nourished by the mother’s milk.

Hormonal Regulation: Male and female reproductive hormones (testosterone, estrogen, and progesterone) control reproductive functions.

Q. How does the embryo get nourishment inside the mother’s body?

Answer:

The embryo gets nourishment through the placenta, a special organ that connects the mother’s blood supply to the baby. The placenta:

Transfers oxygen and nutrients from the mother’s blood to the embryo.

Removes waste products from the embryo’s blood.

Helps in hormone production for pregnancy maintenance.

This ensures proper growth and development of the baby inside the uterus.

Q. Why does menstruation occur?

Answer:

Menstruation occurs when fertilization does not take place. The female body prepares for pregnancy every month by thickening the uterus lining. If fertilization does not occur:

The uterus lining breaks down.

It is released through the vagina as blood and tissue (menstrual flow).

This cycle repeats every 28 days.

It is a natural process in females from puberty to menopause.

Q.  What are the different methods of contraception? How do they work?

Answer:

Contraceptive methods prevent unwanted pregnancy. They include:

1. Barrier Methods:

Condoms and Diaphragms prevent sperm from reaching the egg.

2. Hormonal Methods:

Oral pills prevent ovulation.

Injections/implants release hormones that stop egg release.

3. Intrauterine Devices (IUDs):

Copper-T is placed in the uterus to prevent fertilization.

4. Surgical Methods:

Vasectomy (in males): Cutting of vas deferens to prevent sperm transport.

Tubectomy (in females): Cutting of fallopian tubes to prevent egg movement.

These methods help in birth control and prevent sexually transmitted diseases (STDs).

Q. How are the modes of reproduction different in unicellular and multicellular organisms?

Answer:

Unicellular organisms reproduce mainly by asexual methods, while multicellular organisms use both asexual and sexual reproduction for continuity of life.