Chapter – 7

How do Organisms Reproduce?

In this post we have given the detailed notes of class 10 Science Chapter 7 (How do Organisms Reproduce?) in English. These notes are useful for the students who are going to appear in class 10 board exams.

Chapter 7: How do Organisms Reproduce?

What is Reproduction? 🌱

• Reproduction is the biological process by which an organism (plant or animal) gives rise to another organism similar to itself, thereby increasing the number of individuals of its own species. 🐣
• Reproduction is a characteristic feature of all living organisms. Every organism arises from a pre-existing living organism — a living being is never produced from non-living matter (viruses are a possible exception).
• Reproduction serves two purposes: the survival of the individual species over time, and the maintenance of body design stable enough to be suited to the surrounding environment. Both purposes depend on nutrition — nutrition is the basis of maintenance, growth, and reproduction. 🍃
• Both plants and animals are living organisms; biological events occur in both, and although the basic mode of reproduction is similar, there are minor differences in detail — hence the two are studied separately.

Importance of DNA Copying in Reproduction 🧬

• The DNA present in the chromosomes inside the cell’s nucleus carries the genetic information (the “blueprint” for body design) that passes from parents to offspring.
• Reproduction is essentially about creating a copy of this DNA and providing the extra cellular apparatus needed to package it into a new cell.
• DNA copying during reproduction is not always perfectly accurate. Some variations arise in the copies, and while most of these variations are neutral or harmful, some useful variations do get passed on to the offspring.

Importance of Variation

• If a population is well suited to its habitat (ecosystem), but the habitat undergoes a drastic change (temperature, water level, etc.), the entire population could be wiped out. However, if some variation exists among individuals of the population, there is a better chance that at least some of them will survive such changes.
• Variation is thus useful for the survival of a species over long periods of time, and it forms the basis of biological evolution.

Types of Reproduction 🔬

• Asexual Reproduction
• Sexual Reproduction

Asexual Reproduction: The mode of reproduction in which only a single organism is involved is called asexual reproduction.

Sexual Reproduction: The mode of reproduction in which both male and female individuals are involved is called sexual reproduction.

Difference between Asexual and Sexual Reproduction

Methods of Asexual Reproduction 🧫

• Fission
• Binary fission
• Multiple fission
• Fragmentation
• Regeneration
• Budding
• Spore formation
• Vegetative propagation

1. Fission: In this method of reproduction, a single parent cell divides into two or more daughter cells.

• Binary fission: The organism splits into two cells. Example: Amoeba, Leishmania.
• Multiple fission: The organism splits into many cells at once. Example: Plasmodium (the malaria parasite).

2. Fragmentation: In this method, simple multicellular organisms break up into smaller pieces (fragments) upon maturing, and each fragment grows into a new complete organism. Example: Spirogyra.

3. Regeneration: If an organism happens to get cut or broken into several pieces, many of the pieces grow into separate complete organisms. Example: Planaria, Hydra.

4. Budding: A small outgrowth called a bud develops on the body of the organism. This bud gradually grows into a complete individual and eventually detaches from the parent. Example: Hydra, Yeast.

5. Spore formation: Some organisms develop tiny blob-like structures (sporangia) at the tips of their vertical hyphae/filaments, which contain spores. Spores are covered by a thick, protective wall that allows them to survive unfavourable conditions. When conditions are favourable, spores germinate to form new organisms.

6. Vegetative propagation: In some plants, a new plant develops from a vegetative part such as the root, stem, or leaves — this is called vegetative propagation.

Natural methods of vegetative propagation:

• Through roots: Dahlia, sweet potato
• Through stems: Potato, ginger
• Through leaves: Bryophyllum has buds along the margins of its leaves, which develop into new plants.

Artificial methods of vegetative propagation:

• Grafting: Mango
• Cutting: Rose
• Layering: Jasmine (Chameli)
• Tissue culture: Orchids, ornamental plants

Advantages of vegetative propagation:

• New plants can be produced for plants that do not produce viable seeds, such as banana, rose, etc.
• New plants are genetically identical to the parent.
• It helps in growing seedless fruits.
• It is a cheap and easy method of growing plants.

7. Spore formation in fungi (e.g. Rhizopus): In this method of asexual reproduction, tiny round structures form at the tips of the erect hyphae/threads of some simple multicellular organisms. These blob-like structures are sporangia containing spores, which grow to produce new individuals of organisms like Rhizopus.

Tissue Culture 🧪

Tissue culture is the technique in which various body tissues or cells can be grown and nourished outside the body in an artificial nutrient medium, provided the required conditions are maintained. It is well known that different cells of the body have the ability to grow and generate more cells like themselves in response to various stimuli. It is also known that living organisms maintain an internal environment (sometimes called the “milieu intérieur”) that is more important than external conditions in regulating the activity of living tissue. Tissue culture technique was developed with the basic aim of studying the functional properties of cells and determining how they are affected by, and how they in turn affect, their external environment. For this, it was necessary to isolate cells and keep them alive in an artificial medium, free from the influence of the whole organism.

Example: Orchids, ornamental plants.

Difference between Binary Fission and Multiple Fission

Sexual Reproduction 👫

• In this method of reproduction, two individual organisms participate to produce new offspring. In other words, both male and female sexes are required to produce new offspring.
• Sexual reproduction takes place through the fusion of male and female gametes.
• The process by which male and female gametes fuse is called fertilisation.
• Sexual reproduction results in variation among the offspring.

Why is DNA Copying Essential for Reproduction?

DNA copying is an essential part of the reproductive process, because it ensures that the body design of the organism remains largely stable, which in turn allows the organism to remain suited to its habitat/niche.

Sexual Reproduction in Flowering Plants 🌸

In angiosperms (flowering plants), the reproductive organs are located in the flower — the sepals, petals, stamens, and pistil (carpel). The stamen and pistil are the reproductive parts of the flower, and they contain the reproductive cells.

Types of Flowers

1. Unisexual flowers: When a flower has either only stamens or only a pistil, it is called a unisexual flower. Example: Papaya, watermelon.

2. Bisexual flowers: When a flower has both stamens and a pistil, it is called a bisexual flower. Example: Hibiscus, mustard.

Process of Seed Formation

• Pollen grains produced in the anther are transferred by wind, water, or animals to the stigma of the same flower (self-pollination) or of another flower (cross-pollination).
• A pollen tube grows out of the pollen grain and travels through the style to reach the ovule.
• Fertilisation occurs inside the ovary between the male and female gametes, forming a zygote.
• The zygote divides several times to form an embryo within the ovule, and the ovule develops a tough coat, gradually turning into a seed.
• The ovary develops into a fruit, and the other parts of the flower wither and fall off.

Germination

• The process by which the seed (future plant)/embryo develops into a seedling under favourable conditions is called germination.

Difference between Pollination and Fertilisation

Reproduction in Human Beings 👶

• Human beings become capable of sexual reproduction only after reaching a certain age — this stage is called puberty. In complex multicellular organisms like humans, special reproductive organs exist for the production of sperm and eggs, for the fertilisation of sperm and egg, and for the growth and development of the zygote into a baby.
• Sexual maturation: The period of life when the testes begin producing sperm in males and the ovaries begin producing eggs in females is called puberty (adolescence).

Changes at Puberty

Common in both boys and girls:

• Growth of thick hair in the armpits and genital area.
• Skin becomes oily and pimples/acne may appear.

In girls:

• Increase in breast size.
• Onset of menstruation.

In boys:

• Appearance of facial hair (beard and moustache).
• Cracking/deepening of voice.

These changes are signs that sexual maturation is taking place.

Male Reproductive System

The organs that produce germ cells, together with the organs that transport these germ cells to the site of fertilisation, together make up the male reproductive system. The male reproductive system has several external and internal organs. Two of these are visible externally — the testes and the penis, with the scrotal sac. These organs are connected by ducts (vas deferens). The prostate gland and the urethra of the system lie inside the body.

1. Testes: Sperm are produced in the testes. The testes lie outside the abdominal cavity, in the scrotum, because sperm production requires a temperature lower than normal body temperature.

• The testes also produce the hormone testosterone.

Functions of testosterone:

• Regulates the production of sperm.
• Brings about changes in appearance seen in boys at puberty.

2. Vas deferens: Sperm produced in the testes are carried away by the vas deferens, which join with a tube coming from the urinary bladder to form a common duct.

3. Urethra: This is the passage through which both urine and semen leave the body. With its outer covering, it is called the penis.

4. Associated glands: The seminal vesicle and the prostate gland add their secretions into the vas deferens.

As a result:

• The sperm are transported in a fluid medium.
• This fluid provides nutrition to the sperm.
• It helps in the transport of sperm. Sperm together with the secretions of these glands make up semen.

Female Reproductive System

1. Ovary:

• The female gamete or egg is produced in the ovary.
• A girl’s ovaries already contain thousands of immature eggs at the time of her birth.
• At puberty, some of these eggs start maturing.
• One of the two ovaries releases one mature egg every month.
• The ovary also produces the hormones oestrogen and progesterone.

2. Oviduct (Fallopian tube):

• It carries the egg produced by the ovary to the uterus.
• Fertilisation of the egg with sperm takes place here.

3. Uterus:

• It is a sac-like structure where the development of the baby takes place.
• The uterus opens into the vagina through the cervix.

When the Egg is Fertilised

The fertilised egg is called a zygote, and it gets implanted in the uterus. After implantation in the uterus, the zygote divides and differentiates repeatedly, and an embryo is formed.

When the Egg is Not Fertilised

• Every month, the uterus prepares itself to receive a fertilised egg.
• The uterine lining becomes thick and spongy, ready to nourish a developing embryo.
• If fertilisation does not occur, this lining is not needed and gradually breaks down and comes out through the vagina as blood and mucus.
• This cycle takes about a month and is called menstruation.
• After 45–50 years of age, the ovaries stop releasing eggs, and as a result menstruation stops — this is called menopause.

Placenta 🩸

The placenta is a special structure that develops inside the uterus during pregnancy. It provides oxygen and nutrition to the growing baby. The placenta is connected to the baby through the umbilical cord.

Main functions of the placenta:

• Provides glucose, oxygen, and other nutrients from the mother’s blood to the embryo.
• Removes the waste substances produced by the embryo.

Gestation Period

• The period from fertilisation of the egg to the birth of the baby is called the gestation period. Its duration is approximately 9 months in humans.

Reproductive Health

• Reproductive health means being well in all aspects related to reproduction — physically, mentally, socially, and behaviourally.

Sexually Transmitted Diseases (STDs)

Many diseases can also spread through sexual contact, for example:

• Bacterial: Gonorrhoea, syphilis
• Viral: Warts, HIV-AIDS

The use of condoms can help prevent the transmission of such diseases to a certain extent.

Contraception

Preventing pregnancy is called contraception. Contraceptive methods can prevent the release/formation of eggs, or block fertilisation, and some involve taking medicines that alter the hormonal balance. These methods can also have other side effects.

Types of Contraception

1. Mechanical/barrier methods:

These prevent sperm from reaching the egg.

Examples:

• Condoms, which cover the penis.
• Cervical caps, placed inside the vagina.

2. Chemical methods:

• Medicines (oral pills) are taken by females that alter the hormonal balance and prevent egg release.
• These can have other side effects too.

IUCD (Intra Uterine Contraceptive Device):

A loop or Copper-T is placed inside the uterus, which prevents pregnancy.

Surgical methods:

• Vasectomy: In males, the vas deferens is blocked to prevent the transport of sperm.
• Tubectomy: In females, the fallopian tube is blocked to prevent the transport of the egg.

Female Foeticide

• Killing a female foetus in the womb after determining its sex is called female foeticide.
• A balanced sex ratio is essential for a healthy society. This is only possible when people are made aware, and practices like female foeticide and pre-natal sex determination are stopped.

Key Points to Remember

• Reproduction is the process by which organisms produce new individuals of their own kind, and it is essential for continuation of the species. 🌱
• DNA copying is central to reproduction and is not always accurate, generating variations that are important for evolution. 🧬
• Asexual reproduction (fission, fragmentation, regeneration, budding, spore formation, vegetative propagation) involves a single parent and produces offspring identical to it. 🧫
• Sexual reproduction involves male and female gametes, produces variation, and occurs through pollination and fertilisation in plants. 🌸
• Puberty is marked by sexual maturation, with common and sex-specific changes in boys and girls. 👦👧
• The male reproductive system consists of testes, vas deferens, urethra, and associated glands, producing sperm and semen.
• The female reproductive system consists of ovaries, fallopian tubes, and uterus; fertilisation occurs in the fallopian tube.
• The placenta nourishes the developing baby, and the gestation period in humans is about 9 months. 🩸
• Contraceptive methods (mechanical, chemical, surgical) help control reproduction and family size.
• Reproductive health awareness and prevention of female foeticide are essential for a healthy society.

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