How Do Organisms Reproduce Class 10 Notes – CBSE Biology Made Simple (2025

How do Organisms Reproduce? Class 10 Notes

Explore our complete Class 10 Biology notes for Chapter 7 – “How Do Organisms Reproduce?” Understand various modes of reproduction in plants and animals, from budding to sexual reproduction. This concise and informative guide simplifies key concepts and helps you grasp the core processes that ensure life’s continuity. Dive into the fascinating world of reproduction and strengthen your CBSE exam preparation today!

Subject	Science (Biology)
Class	10
Board	CBSE & State Boards
Chapter No.	7
Chapter Name	How do Organisms Reproduce?
Type	Notes
Session	2025-26

Need for Reproduction:

Organisms need energy for survival which they obtain from life processes such as nutrition and respiration.
Reproduction does not provide energy. It needs a lot of energy.
Genetic material is transferred from one generation to the next as a result of reproduction through DNA copying.
DNA copying takes place with high constancy and considerable variations, which is advantageous to the species for stability in the changing environment.

Variation and its Importance:

Variation is important for the survival of a species but can sometimes be harmful to an individual because:

Adapting to change: Variations make the population diverse, meaning some individuals might have traits that help them survive if the environment changes.
Helping evolution: Over time, helpful variations can build up in the population, leading to new species that are better suited to their environment.
Risk to individuals: Although variation helps the species, some changes might not be good for an individual in their specific environment, which could make it harder for them to survive.

Modes of Reproduction Used by Single Organisms

i. Fission

For unicellular organisms, cell division, or fission, leads to the creation of new individuals.

ii. Fragmentation

In multi-cellular organisms with relatively simple body organization, simple reproductive methods can still work. Spirogyra, for example, simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals.

It is not possible to reconstruct the whole organism from a fragment in complex multicellular organisms because many multi-cellular organisms are not simply a random collection of cells. Specialized cells are organized as tissues and tissues are organized into organs, which then have to be placed at definite positions in the body. Therefore, the cell-by-cell division would be impractical.

iii. Regeneration

Many fully differentiated organisms have the ability to give rise to new individual organisms from their body parts. That is, if the individual is somehow cut or broken up into many pieces, many of these pieces grow into separate individuals. For example, simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is known as regeneration.

iv. Budding

In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals. Yeast also follows budding for reproduction.

v. Vegetative Propagation

The method of producing new plants from vegetative parts like roots, stems, and leaves are called vegetative propagation.

Buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and develop into new plants.

leaf of bryophyllum with buds class 10 science how do organisms reproduce

The advantages of vegetative propagation are:

Faster growth and earlier flowering and fruiting.
Preservation of desired traits.
Propagation of seedless varieties.

Disadvantages of vegetative propagation are:

Such plants are genetically similar to parent plants and are vulnerable to infections and diseases.
They do not have variations, therefore, do not adapt well to changing environments, and the plant species do not evolve.

vi. Spore Formation

The thread-like structures that develop on bread are the hyphae of the bread mould (Rhizopus). They are non-reproductive parts. The tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individuals.

Advantages of spore formation:

Survival in Harsh Conditions: Spores are highly resistant to extreme conditions like heat, cold, and drought. This helps the organism survive unfavorable environments.
Wide Dispersal: Spores are lightweight and can easily be carried by wind, water, or animals to distant places. This increases the chances of colonizing new environments.
Rapid Population Increase: Spores are produced in large numbers, ensuring that even if many are destroyed, some will still survive and grow into new organisms.

Advantages of the asexual mode of reproduction

Only one individual is required.
Progeny is identical to parents.
Produced in large numbers.

Sexual Reproduction

It is a mode of reproduction that depends on the involvement of two individuals before a new generation can be created.

Four steps in sexual reproduction:

Formation of gametes in the sex organs.
Transfer of male gamete to female gamete.
Fusion of gametes, either inside or outside the female parent's body.
Development of the zygote to embryo and then complete individual.

Advantages of sexual reproduction:

Variations are produced among the progeny.
Such populations are able to adapt well to changing environment and thus evolves faster.

Asexual reproduction	Sexual reproduction
i. Involves only one parent.	i. It involves two parents.
ii. Gametes are not produced.	ii. Gametes are produced.
iii. No fertilization and zygote formation.	iii. Fertilization and zygote formation is observed.
iv. Produces offspring less rapidly.	iv. Produces offspring more rapidly.

Sexual Reproduction in Flowering Plants

Different parts of a flower are – sepals, petals, stamens, and pistils. The stamens and pistils are the reproductive parts of a flower that contain the germ cells.

longitudinal section of flower class 10 science

The flower may be

unisexual (papaya, watermelon) when it contains either stamens or pistils
bisexual (Hibiscus, mustard) when it contains both stamens and pistils.

Stamen is the male reproductive part and it produces pollen grains that are yellowish in colour.
Pistil is present in the center of a flower and is the female reproductive part. It is made of three parts: stigma, style, and ovary.
The ovary contains ovules and each ovule has an egg cell.
The male germ cell produced by pollen grain fuses with the female gamete present in the ovule.
This fusion of the germ cells or fertilization gives us the zygote which is capable of growing into a new plant.

Pollination	Fertilization
i. It is the transfer of pollen grain from the anther to the stigma of a flower.	i. It is the fusion of the male gamete with the female gamete.
ii. It is achieved by agents like wind, water, or animals.	ii. It is achieved by the growth of the pollen tube so that the male gamete reaches the female germ cells.
iii. It leads to fertilization.	iii. It leads to the formation of seeds.
iv. It is an external process.	iv. It is an internal process.

Process of seed formation in a flowering plant:

The pollen from the stamen is transferred to the stigma.
The male germ cell and the female germ cells combine to form the zygote.
The zygote undergoes rapid division to form the embryo inside the ovule.
The ovule develops a seed coat and turns into a seed.

germination class 10 science — *Germination*

Self-pollination	Cross-pollination
i. It is the transfer of pollen grains from the anther to the stigma within the same flower.	i. It is the transfer of pollen grains from the anther to the stigma in another flower.
ii. It occurs either in the same flower or another flower of the same plant.	ii. It occurs between two flowers that are on different plants but are of the same species.
iii. It occurs in flowers that are genetically the same.	iii. It occurs between flowers that are genetically different.

Reproduction in Human Beings

The ratio of number of chromosomes between an egg and its zygote is 1:2.
Sperms contain either X or Y chromosomes whereas an egg will always have an X chromosome.

General Growth	Sexual Maturation
General growth refers to different types of developmental processes in the body like an increase in height, weight gain, and changes in shape and size of the body.	Sexual maturation is specific to changes reflected at puberty like the cracking of voice, new hair patterns, development of breasts in females, etc.

Sexual maturation of reproductive tissues is a necessary link for reproduction because of the need for specialized cells called germ cells to participate in sexual reproduction. The body of the individual organism has to grow to its adult size, the rate of general body growth begins to slow down, and reproductive tissues begin to mature.

A whole new set of changes in the appearance of the body takes place like changes in body proportions, and new features appear. This period during adolescence is called puberty.

There are also changes taking place that are different between boys and girls. In girls, breast size begins to increase, with darkening of the skin of the nipples at the tips of the breasts. Also, girls begin to menstruate at around this time. Boys begin to have new thick hair growth on their faces and their voices begin to crack.

Male Reproductive System

The urethra serves as a common passage for both sperm and urine.
The testosterone hormone is released by the testis. In addition to regulating the formation of sperm, testosterone brings about changes in appearance seen in boys at the time of puberty.
The prostate gland and the seminal vesicles add their secretions so that the sperms are now in a fluid which makes their transport easier and this fluid also provides nutrition.

Female Reproductive System

Ovary (production of egg)
Oviduct (site of fertilization)
Uterus (site of implantation)
Vagina (entry of the sperm)

Functions of the ovary:

Production of the female hormone estrogen.
Production of female gamete.

Functions of Oviduct/Fallopian tube:

Transfer of female gamete from the ovary.
Site of fertilization.

Functions of the uterus:

Implantation of the zygote.
Nourishment of developing embryo.

Placenta: A placenta is a special tissue connection between the embryo and the uterine wall.

Role of the Uterus and Placenta in the Growth and Development of the Embryo:

The lining of the uterus thickens and is richly supplied with blood to nourish the growing embryo.
The embryo gets nutrition from the mother’s blood with the help of the placenta. It is embedded in the uterine wall.
It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi.
This provides a large surface area for nutrition and oxygen to pass from the mother to the embryo.
Waste substances produced by the embryo are removed through the placenta into the mother’s blood.
The child is born as a result of rhythmic contractions of the muscles in the uterus.

When the egg is not fertilized:

The egg survives for a day in the reproductive system.
In case the egg is not fertilized, it is shed along with the lining of the uterus out of the vagina as blood and mucus.

Child marriages are a hazard to women's reproductive health because:

Females will not have reached full sexual maturity at the time of marriage.
There are possibilities of pregnancy in the teenage years that may cause adverse effects on the female’s body.

Contraceptive methods are used such as:

Mechanical barriers (condoms)
Drugs (as pills)
Loop or copper T
Surgical method.

Pills change the hormonal balance and thus prevent the release of the egg, hence fertilization is prevented. But this method can have some side effects as it interferes with the hormonal balance of the body.

Advantages of using a mechanical barrier over other contraceptive measures:

Contraceptive pills can cause hormonal imbalances.
Copper T and IUD can cause irritation to the uterine lining if not placed correctly.
Surgical methods, if not performed properly, can lead to infections and complications.

🧬 Class 10 Science Chapter 8: How Do Organisms Reproduce?

📘 NCERT Solutions (Intext + Exercise) | CBSE Board | 2025–26

📖 Intext Questions – Page 128

Q1. What is the importance of DNA copying in reproduction?
✅ Answer:
DNA copying ensures that genetic information is passed from parent to offspring. It also introduces variations necessary for evolution and adaptation.

Q2. Why is variation beneficial to the species but not necessarily for the individual?
✅ Answer:
Variations help a species survive environmental changes. An individual may not benefit directly, but the species as a whole becomes more adaptable.

📖 Intext Questions – Page 133

Q1. How does binary fission differ from multiple fission?
✅ Answer:

Binary Fission	Multiple Fission
Parent divides into 2	Parent divides into many
E.g. Amoeba	E.g. Plasmodium
Occurs under normal conditions	Occurs in unfavorable conditions

Q2. How will an organism be benefited if it reproduces through spores?
✅ Answer:

Spores can survive harsh conditions
Spread easily through wind or water
Help in rapid reproduction

Q3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
✅ Answer:
Complex organisms have specialized cells and organ systems. Regeneration is limited to healing or repair, not complete individual formation.

Q4. Why is vegetative propagation practiced for growing some types of plants?
✅ Answer:

Fast and assured reproduction
Identical quality as parent plant
Useful for plants that don’t produce viable seeds (e.g., banana, rose)

Q5. Why is DNA copying an essential part of the process of reproduction?
✅ Answer:
DNA copying ensures transmission of genetic information, continuity of life, and introduces variations.

📖 Intext Questions – Page 140

Q1. How is the process of pollination different from fertilization?
✅ Answer:

Pollination	Fertilization
Transfer of pollen to stigma	Fusion of male and female gametes
Occurs before fertilization	Occurs after successful pollination

Q2. What is the role of seminal vesicles and prostate gland?
✅ Answer:
They secrete fluids that:

Nourish sperm
Provide medium for movement
Protect sperm from acidic environment

Q3. What are the changes seen in girls at the time of puberty?
✅ Answer:

Breast development
Menstruation begins
Hips broaden
Growth of hair in armpits and pubic area

Q4. How does the embryo get nourishment inside the mother's body?
✅ Answer:
The placenta connects the embryo to the mother’s blood supply, allowing transfer of oxygen, nutrients, and waste.

Q5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?
✅ Answer:
No. Copper-T prevents pregnancy but not STDs. Barrier methods like condoms are needed for STD protection.

📘 NCERT Exercise Questions (Page 142–143)

Q1. Asexual reproduction takes place through budding in:
(a) Amoeba
(b) Yeast
(c) Plasmodium
(d) Leishmania
✅ Answer: (b) Yeast

Q2. Which of the following is not a part of the female reproductive system in humans?
(a) Ovary
(b) Uterus
(c) Vas deferens
(d) Fallopian tube
✅ Answer: (c) Vas deferens

Q3. The anther contains:
(a) Sepals
(b) Ovules
(c) Carpel
(d) Pollen grains
✅ Answer: (d) Pollen grains

Q4. What are the advantages of sexual reproduction over asexual reproduction?
✅ Answer:

Produces genetic variation
Increases adaptability
Helps evolution and survival in changing environments

Q5. What are the functions performed by the testis in human beings?
✅ Answer:

Produces sperm
Secretes testosterone hormone

Q6. Why does menstruation occur?
✅ Answer:
If fertilization doesn’t occur, the thickened uterine lining and blood vessels are shed through the vagina.

Q7. Draw a labelled diagram of the longitudinal section of a flower.
✅ Answer:
(Diagram should include: petals, sepals, anther, filament, stigma, style, ovary, ovule)

Q8. What are the different methods of contraception? Explain.
✅ Answer:

Barrier methods – Condoms, diaphragms
Chemical methods – Oral pills
Surgical methods – Vasectomy, tubectomy
Intrauterine devices – Copper-T
They help prevent fertilization or implantation.

Q9. How are the modes of reproduction different in unicellular and multicellular organisms?
✅ Answer:

Unicellular Organisms	Multicellular Organisms
Asexual (fission, budding)	Asexual and sexual (higher forms)
Whole body involved	Only reproductive organs involved

Q10. How does reproduction help in providing stability to populations of species?
✅ Answer:
Reproduction ensures the continuity of species and replaces individuals lost to death, maintaining population balance.

Q11. What could be the reasons for adopting contraceptive methods?
✅ Answer:

To control population
To prevent unwanted pregnancy
To protect against STDs
For maternal health and spacing children

🧬 Chapter 8 – How Do Organisms Reproduce?

📚 CBSE Board Exam – Previous Year Questions

🟢 1-MARK QUESTIONS

Name the part of a flower where pollen grains are produced.
📅 CBSE 2019
✅ Answer: Anther
Define the term ‘fertilization’.
📅 CBSE 2018
✅ Answer: Fusion of male and female gametes to form a zygote.
What is the function of the placenta in human female?
📅 CBSE 2020
✅ Answer: Facilitates the exchange of nutrients, gases, and waste between mother and fetus.
State the method used for growing rose plants.
📅 CBSE 2017
✅ Answer: Vegetative propagation (stem cutting)
What is the full form of STD? Give one example.
📅 CBSE 2016
✅ Answer: Sexually Transmitted Disease; e.g., AIDS or syphilis.

🟡 2-MARK QUESTIONS

Differentiate between asexual and sexual modes of reproduction.
📅 CBSE 2020

Asexual	Sexual
One parent involved	Two parents involved
No gametes involved	Gametes involved
No variation	Variations occur

List two advantages of vegetative propagation.
📅 CBSE 2019
✅ Answer:

Fast reproduction
Identical to parent (preserves traits)

What happens when: (i) a mature ovum is not fertilised? (ii) a mature ovum is fertilised?
📅 CBSE 2022
✅ Answer:
(i) Menstruation occurs.
(ii) Zygote forms, which develops into an embryo.

🟠 3-MARK QUESTIONS

Explain budding in Hydra with the help of a diagram.
📅 CBSE 2018
✅ Answer: Diagram + explanation showing small outgrowth (bud) developing and detaching.

How is the process of pollination different from fertilization? Explain.
📅 CBSE 2017

Pollination	Fertilization
Transfer of pollen to stigma	Fusion of male and female gametes
External process	Internal process

What are sexually transmitted diseases (STDs)? Name two STDs and mention two ways to prevent them.
📅 CBSE 2023
✅ Answer:

STDs spread via sexual contact
Examples: AIDS, gonorrhea
Prevention: Use of condoms, monogamous relationships

Draw a labelled diagram of the female reproductive system.
📅 CBSE 2016
✅ Answer: Labels include: ovary, fallopian tube, uterus, cervix, vagina

How does binary fission occur in Amoeba? Explain with the help of a diagram.
📅 CBSE 2021 (Compartment)

🔵 5-MARK QUESTIONS

Describe the male reproductive system in humans. Label the parts in a diagram.
📅 CBSE 2020

Testes, vas deferens, seminal vesicle, prostate gland, penis
Functions: sperm production, transport, nourishment

Explain the process of fertilization and development in human beings.
📅 CBSE 2019
✅ Answer:

Fertilization in fallopian tube
Zygote formation → embryo → implantation in uterus
Placenta supports fetal development

Draw a well-labelled diagram of a flower showing its reproductive parts. Describe the function of any two parts.
📅 CBSE 2018

Stamen (anther + filament) → produces pollen
Carpel (stigma, style, ovary) → female reproductive organ

What are the methods of contraception? How do they prevent pregnancy?
📅 CBSE 2022
✅ Answer:

Method	Action
Barrier	Blocks sperm (e.g., condoms)
Chemical	Hormonal pills prevent ovulation
Surgical	Vasectomy/tubectomy – blocks gamete transport

📌 Frequently Tested Topics in CBSE Exams

Topic	Question Types	Frequency
Human Reproductive System	Diagram, 5M	Very High
Asexual Reproduction (Budding, Fission)	3M, Diagram	High
Menstrual Cycle, Fertilization	2M, 3M	High
Contraceptive Methods	3M, 5M	High
Flower Structure, Pollination	1M, 3M	Medium
STD Awareness	2M	Medium

Feature	Binary Fission	Multiple Fission
Number of daughter cells	Two	Many
Division process	Parent cell divides into two equal halves	Parent cell divides into multiple daughter cells simultaneously
Examples	Many bacteria and protozoa like Amoeba, Paramecium, and Leishmania.	Plasmodium (malarial parasite).
Speed of division	Relatively faster	Relatively slower
Complexity	Simpler	More complex
Diagram	iv.	iv.

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