How do organisms Reproduce? class 10 Notes

How do organisms Reproduce?

Introduction

Reproduction is one of the most important characteristics of living organisms. It is the biological process by which organisms produce new individuals of their own kind. Although reproduction is not essential for the survival of an individual, it is necessary for the continuity and survival of a species on the Earth.

Do Organisms Create Exact Copies of Themselves?

No, organisms do not create exact copies of themselves. Although offspring resemble their parents, they are never completely identical.
This happens due to variations that occur during the process of reproduction.

Why Exact Copies Are Not Produced?

1. DNA Copying Is Not Perfect

During reproduction, DNA is copied from parent to offspring.
The copying of DNA is not 100% accurate.
Small errors may occur during DNA replication, leading to variations.

2. Role of Variations

Variations are small differences between parents and offspring.
These differences may be in:

Height
Skin color
Shape and size
Resistance to diseases

3. Variations Are Important for Survival

Variations help organisms adapt to changing environments.
If the environment changes suddenly, some variations may help organisms survive.
This is the basis of evolution.

4. Asexual vs Sexual Reproduction

Asexual reproduction:
- Produces offspring very similar to parents.
- Example: Amoeba, Hydra
- Still, minor variations occur due to DNA copying.
Sexual reproduction:
- Offspring show more variations.
- Because DNA comes from two parents.

5. Example

If all bacteria were exactly the same, a single disease could destroy the entire population.
Due to variation, some bacteria survive and multiply.

The Importance of Variation

Variation refers to the differences found among individuals of the same species. These differences may be in physical appearance, structure, behaviour, or genetic makeup.
Variations arise due to errors in DNA copying and sexual reproduction.

Why Is Variation Important?

1. Helps in Survival of Species

Environmental conditions such as climate, food availability, and diseases keep changing.
Variations increase the chances that some individuals will survive under changed conditions.
Thus, variation ensures the continuity of a species.

2. Basis of Evolution

Variations are the raw material for evolution.
Over long periods, useful variations accumulate.
This leads to the formation of new species.

3. Provides Adaptability

Organisms with favourable variations adapt better to their environment.
Example: Bacteria resistant to antibiotics survive and multiply.

4. Prevents Complete Extinction

If all organisms were exactly the same, a single harmful change could wipe out the entire population.
Variations protect a species from complete extinction.

5. Helps in Natural Selection

Nature selects organisms with useful variations.
Such organisms survive, reproduce, and pass on their traits to the next generation.

Examples of Variation

Difference in height, skin colour, eye colour in humans
Different beak shapes in birds
Antibiotic resistance in bacteria

Modes of Reproduction Used by Single Organisms

Single organisms mainly reproduce by asexual reproduction. In this mode of reproduction, only one parent is involved, and no fusion of male and female gametes takes place.
The offspring produced are genetically similar to the parent, with minor variations.

Asexual Reproduction in Single Organisms

1. Fission

Fission is the most common method of reproduction in unicellular organisms.

(a) Binary Fission

One parent cell divides into two identical daughter cells.
Each daughter cell grows into a new organism.

Examples:

Amoeba
Paramecium
Bacteria

Types of Binary Fission:

Irregular – Amoeba
Transverse – Paramecium
Longitudinal – Leishmania

(b) Multiple Fission

The nucleus divides repeatedly.
A single cell produces many daughter cells at the same time.

Example:

Plasmodium (malarial parasite)

2. Budding

A small outgrowth called a bud develops on the parent body.
The bud grows, matures, and then separates to form a new organism.

Examples:

Hydra
Yeast

3. Spore Formation

The parent organism produces spores inside a sporangium.
Spores are light and resistant.
They germinate under favourable conditions.

Examples:

Rhizopus (bread mould)
Other fungi

4. Fragmentation

The parent body breaks into fragments.
Each fragment grows into a complete organism.

Example:

Spirogyra (algae)

5. Regeneration

Ability of an organism to regrow lost parts.
Each part can develop into a complete organism.

Examples:

Planaria
Hydra

Advantages of Asexual Reproduction

Fast and simple process
No need for a partner
Large number of offspring produced in a short time

Disadvantages

Very little variation
Less adaptability to changing environment

Sexual Reproduction

Sexual reproduction involves two individuals (male and female) and leads to greater genetic variation, which increases adaptability and ensures the long-term survival of a species.
Asexual reproduction has limitations because it produces very little variation, making organisms less adaptable to changing environmental conditions.

Why the Sexual Mode of Reproduction?

Sexual reproduction is a mode of reproduction in which two parents, a male and a female, are involved.
It includes the formation and fusion of male and female gametes to produce a zygote, which develops into a new individual.
Although this process is slower than asexual reproduction, it is very important for the survival of species.

Reasons for Sexual Mode of Reproduction

1. Produces Genetic Variation

Sexual reproduction results in the mixing of genetic material from two parents.
This leads to greater variation in offspring.
Variations help organisms survive in changing environments.

2. Helps in Adaptation

Offspring with useful variations are better adapted to their surroundings.
These organisms survive and reproduce successfully.
Thus, sexual reproduction increases the chances of survival of a species.

3. Basis of Evolution

Variations produced during sexual reproduction accumulate over generations.
This leads to evolution and the formation of new species.

4. Removes Harmful Variations

Harmful genes can be eliminated through natural selection.
Sexual reproduction reduces the chances of accumulation of harmful mutations.

5. Prevents Complete Extinction

If a species reproduces only asexually, all individuals will be almost identical.
A sudden environmental change can destroy the entire population.
Sexual reproduction reduces this risk.

Sexual Reproduction in Flowering Plants

Sexual reproduction in flowering plants (angiosperms) involves the formation of male and female gametes, their fusion (fertilisation), and the development of seeds and fruits.
This process ensures genetic variation and continuity of plant species.

Parts Involved in Sexual Reproduction

1. Flower – The Reproductive Organ

A flower is the reproductive part of a flowering plant. It consists of four main whorls:

Sepals – Protect the flower bud
Petals – Attract insects for pollination
Stamen (Male part)
- Anther – Produces pollen grains (male gametes)
- Filament – Supports the anther
Pistil / Carpel (Female part)

Stigma – Receives pollen
Style – Connects stigma to ovary
Ovary – Contains ovules (female gametes)

Steps of Sexual Reproduction in Flowering Plants

1. Pollination

Pollination is the transfer of pollen grains from the anther to the stigma.

Types of Pollination:

Self-pollination – Pollen transferred to the stigma of the same flower or same plant
Cross-pollination – Pollen transferred to the stigma of another flower of the same species

Agents of Pollination:

Wind
Water
Insects
Birds

2. Fertilisation

After pollination, the pollen grain germinates on the stigma.
A pollen tube grows through the style into the ovary.
Male gamete reaches the ovule and fuses with the female gamete.
This fusion is called fertilisation.
A zygote is formed.

3. Development of Seed and Fruit

The zygote develops into an embryo.
Ovule becomes a seed.
Ovary develops into a fruit.
Other parts of the flower usually wither away.

Advantages of Sexual Reproduction in Plants

Produces genetic variation
Helps plants adapt to changing environment
Leads to evolution
Seeds help in dispersal and survival

Reproduction in Human Beings

Human beings reproduce by sexual reproduction, which involves the formation of male and female gametes, fertilisation, and development of the embryo inside the mother’s body.
This process ensures genetic variation and continuity of the human species.

1) Male Reproductive System

The male reproductive system is responsible for the production of male gametes (sperms) and male sex hormones, and for transferring sperms into the female reproductive tract for fertilisation.

Main Parts of the Male Reproductive System

1. Testes

A pair of oval-shaped organs present in the scrotum.
Functions:
- Produce sperms (spermatogenesis)
- Secrete the male hormone testosterone
Testosterone helps in:

Development of male secondary sexual characters
Maturation of reproductive organs

2. Scrotum

A pouch of skin that holds the testes outside the abdominal cavity.
Maintains the temperature of testes about 2–3°C lower than body temperature.
Lower temperature is necessary for sperm formation.

3. Epididymis

Coiled tube attached to each testis.
Functions:

Stores sperms
Allows sperms to mature

4. Vas Deferens (Sperm Duct)

Long muscular tube.
Transports sperms from epididymis to the urethra.

5. Accessory Glands

These glands add fluids to sperms to form semen.

(a) Seminal Vesicles

Secrete fluid rich in fructose.
Provides energy to sperms.

(b) Prostate Gland

Secretes alkaline fluid.
Protects sperms from acidic environment.

(c) Cowper’s Gland (Bulbo-urethral gland)

Secretes mucus-like fluid.
Lubricates urethra.

6. Urethra

Common passage for urine and semen.
Extends through the penis.

7. Penis

External reproductive organ.
Transfers sperms into the female reproductive tract during copulation.

Sperm Structure (Brief)

Head – Contains nucleus with genetic material
Middle piece – Contains mitochondria (energy)
Tail – Helps in movement

Functions of Male Reproductive System

Production of sperms
Secretion of male hormones
Transport of sperms for fertilisation

2) Female Reproductive System

The female reproductive system is responsible for producing female gametes (ova/eggs), secreting female sex hormones, and providing the environment for the development of the embryo and birth of a baby.

Main Parts of the Female Reproductive System

1. Ovaries

Paired, oval-shaped organs located in the pelvic cavity.
Functions:
- Produce ova (eggs) through oogenesis
- Secrete female hormones oestrogen and progesterone
Hormones regulate menstrual cycle and development of secondary sexual characters.

2. Fallopian Tubes / Oviducts

A pair of tubes connecting ovaries to the uterus.
Functions:

Transport ovum from ovary to uterus
Site of fertilisation (where sperm meets ovum)

3. Uterus (Womb)

Hollow, muscular, pear-shaped organ.
Functions:

Receives the fertilised egg (zygote)
Provides nourishment and protection to the developing embryo
Muscular contractions help during childbirth

4. Cervix

Narrow, lower end of the uterus.
Functions:

Connects uterus to vagina
Acts as a passage for sperms and, later, the baby

5. Vagina

Muscular tube leading from the cervix to the external genitalia.
Functions:

Receives sperms during copulation
Acts as the birth canal during delivery
Outlet for menstrual flow

Ova and Fertilisation

Females are born with a fixed number of ova in the ovaries.
Each month, one ovum matures and is released (ovulation).
If sperm meets ovum in the fallopian tube, fertilisation occurs.
Zygote moves to the uterus for implantation and development.

Menstrual Cycle

Monthly cycle (~28–30 days)
Involves ovum maturation, release, and preparation of uterus for pregnancy.
If fertilisation does not occur, menstruation takes place (shedding of uterine lining).

Functions of Female Reproductive System

Production of female gametes (ova)
Secretion of female hormones
Provides environment for fertilisation, embryo development, and childbirth

What Happens When the Egg is Not Fertilised?

In human females, if the ovum (egg) released from the ovary is not fertilised by a sperm, certain changes take place in the body. This is a normal part of the menstrual cycle.

Process When Egg is Not Fertilised

1. Ovulation Occurs

Every month, one ovum matures and is released from the ovary (ovulation).
It moves into the fallopian tube.

2. No Fertilisation

If no sperm reaches the ovum, fertilisation does not occur.
The egg remains unfertilised and eventually disintegrates.

3. Hormonal Changes

The levels of female hormones oestrogen and progesterone fall.
The uterus lining (endometrium), which had thickened to support a possible embryo, breaks down.

4. Menstruation

The broken-down uterine lining, along with blood and the unfertilised egg, is shed from the body through the vagina.
This process is called menstruation or the period.
Menstruation usually lasts 3–7 days.

Importance

Menstruation ensures the uterus is ready for the next cycle.
It is a normal, healthy process in females of reproductive age.

Reproductive Health

Reproductive health refers to the proper functioning of the reproductive system and the well-being of individuals in relation to reproduction.
It involves physical, mental, and social well-being, not just the absence of disease or infirmity in the reproductive organs.
Good reproductive health ensures the ability to reproduce safely and the prevention of reproductive system problems.

Key Aspects of Reproductive Health

1. Care of Reproductive Organs

Maintain personal hygiene of reproductive organs.
Avoid infections of the reproductive system, such as sexually transmitted infections (STIs).

2. Avoiding Sexually Transmitted Diseases (STDs)

STDs are infections that spread through sexual contact.
Common STDs:
- HIV/AIDS
- Syphilis
- Gonorrhoea
Prevention:

Using condoms
Avoiding unsafe sexual practices

3. Family Planning

Family planning ensures a planned number of children and proper spacing between them.
Methods:

Natural Methods: Calendar method, abstinence
Contraceptive Devices: Condoms, diaphragms
Oral Contraceptives: Birth control pills
Surgical Methods: Vasectomy (male), Tubectomy (female)

4. Avoiding Misuse of Drugs and Alcohol

Drugs, alcohol, and smoking can affect reproductive health.
Can lead to infertility or poor sperm/egg quality.

5. Awareness and Education

Knowledge about adolescent changes, menstruation, safe sex, and contraception is important.
Promotes responsible behaviour and informed choices.

6. Healthy Lifestyle

Balanced diet, exercise, and stress management support proper functioning of the reproductive system.

Importance of Reproductive Health

Prevents diseases and infections
Promotes safe pregnancy and childbirth
Ensures healthy babies
Improves overall quality of life
Reduces population-related problems

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