Complete Class 10 Science Notes | SFALXO
Reproduction is the biological process through which organisms produce new individuals of their own kind. It is essential for the continuation of species from one generation to the next.
Organisms belonging to the same species generally have similar body designs. These designs are controlled by the information present in chromosomes in the form of DNA.
DNA stands for Deoxyribonucleic Acid. It contains the instructions required for making proteins, and these proteins help determine the structure and functioning of the organism.
The fundamental event in reproduction is the creation of a copy of DNA. However, a DNA copy cannot survive independently. It must be accompanied by the formation of additional cellular material such as cytoplasm and cell organelles.
Once the DNA and cellular machinery have been duplicated, the cell can divide to form new cells or new individuals.
Variations are differences between individuals of the same species. They arise mainly because DNA copying is not completely error-free.
Variations help populations survive environmental changes. A population may be well adapted to its surroundings, but sudden changes in the environment can threaten its survival.
Variations that provide an advantage may accumulate over generations. Over a long period, this can contribute to the evolution of new forms and species.
Asexual reproduction generally produces offspring that are genetically very similar to the parent, except for small variations caused by DNA copying.
| Mode | Organism or Example | Description |
|---|---|---|
| Binary Fission | Amoeba | One parent cell divides into two daughter cells. |
| Multiple Fission | Plasmodium | One parent cell divides to form many daughter cells. |
| Fragmentation | Spirogyra | The body breaks into fragments, and each fragment grows into a new organism. |
| Regeneration | Planaria, Hydra | Body pieces develop into complete organisms using specialised regenerative cells. |
| Budding | Hydra | A small outgrowth develops on the parent and later separates. |
| Vegetative Propagation | Plants | New plants develop from roots, stems or leaves. |
| Spore Formation | Rhizopus | Spores formed inside sporangia grow into new organisms under suitable conditions. |
Fission is a form of asexual reproduction in which a unicellular organism divides to produce new individuals.
In binary fission, one parent cell divides into two daughter cells.
In multiple fission, the nucleus divides repeatedly and the cytoplasm separates around the nuclei to form many daughter cells.
In simple multicellular organisms such as Spirogyra, the body grows into a mature filament. The filament may break into smaller pieces, and each piece develops into a complete organism.
Regeneration is the ability of certain organisms to develop complete individuals from body fragments.
Organisms such as Planaria and Hydra possess specialised cells that divide rapidly and form a mass of cells. These cells then undergo an organised process called development to form different tissues and organs.
In budding, a small outgrowth called a bud develops at a specific site on the parent organism due to repeated cell division.
Tissue culture is a technique in which a small piece of plant tissue is grown under controlled conditions on a nutrient medium.
In organisms such as Rhizopus, spores are produced inside specialised structures called sporangia.
Sexual reproduction produces greater variation because DNA from two different individuals is combined.
If two normal body cells fused during reproduction, the chromosome number would double in every generation. This would disturb the genetic stability of the species.
Special reproductive cells called gametes contain half the number of chromosomes present in normal body cells. This reduction occurs through a specialised division called meiosis.
Flowers are the reproductive structures of flowering plants. They contain male and female reproductive organs.
| Structure | Function |
|---|---|
| Anther | Produces pollen grains containing male gametes. |
| Stigma | Receives pollen grains. |
| Style | Provides the pathway for pollen tube growth. |
| Ovary | Contains ovules and later develops into the fruit. |
| Ovule | Contains the egg cell and later develops into a seed. |
Pollination may occur through wind, water, insects, birds or other animals.
Under suitable conditions of water, oxygen and temperature, the embryo inside a seed develops into a seedling.
Human reproduction involves specialised reproductive organs and the formation of male and female gametes.
The testes are located in the scrotum outside the abdominal cavity. Sperm formation requires a temperature slightly lower than the normal body temperature.
The testes perform two major functions:
Fluids from the prostate gland and seminal vesicles are added to the sperm. These fluids provide nourishment and help in the transport of sperm.
| Part | Function |
|---|---|
| Testes | Produce sperm and testosterone. |
| Scrotum | Maintains a suitable lower temperature for sperm formation. |
| Vas Deferens | Transports sperm. |
| Prostate and Seminal Vesicles | Add fluids that nourish and transport sperm. |
| Urethra | Passage through which semen leaves the body. |
The ovaries produce female gametes called eggs and secrete female reproductive hormones.
Generally, one mature egg is released by an ovary approximately once every month.
The egg enters the fallopian tube, also called the oviduct. Fertilisation generally occurs in this tube if sperm are present.
The uterus is the organ where the embryo implants and develops. Its inner lining becomes thick and richly supplied with blood to support pregnancy.
Fertilisation occurs when the male gamete fuses with the female gamete to form a single cell called the zygote.
The zygote undergoes repeated divisions and forms an embryo. The embryo attaches itself to the thickened lining of the uterus. This process is called implantation.
The placenta is a specialised disc-like tissue that connects the developing embryo with the mother.
Every month, the uterine lining becomes thick and richly supplied with blood in preparation for a possible pregnancy.
If fertilisation does not occur, the egg is not implanted and the thickened uterine lining is no longer required.
The lining breaks down and is discharged through the vagina as blood and mucus. This is called menstruation.
The menstrual flow commonly lasts for approximately 2 to 8 days, although duration may vary.
Reproductive health includes awareness about reproductive organs, hygiene, sexually transmitted diseases, contraception and responsible reproductive choices.
Sexually transmitted diseases, or STDs, are infections that may spread through sexual contact.
| Type | Examples |
|---|---|
| Bacterial Diseases | Gonorrhoea, Syphilis |
| Viral Diseases | Genital warts, HIV-AIDS |
Contraception refers to methods used to prevent unwanted pregnancy.
| Method | Examples | Working Principle |
|---|---|---|
| Barrier Methods | Condoms and other physical barriers | Prevent sperm from reaching the egg. Condoms can also reduce the risk of certain STDs. |
| Hormonal Methods | Oral contraceptive pills | Alter hormonal balance and may prevent the release of an egg. |
| Intrauterine Devices | Copper-T and other IUDs | Placed inside the uterus to prevent fertilisation or implantation. |
| Surgical Methods | Vasectomy and Tubectomy | Block the pathways through which sperm or eggs travel. |
In vasectomy, the vas deferens are cut or blocked to prevent sperm from entering the semen.
In tubectomy, the fallopian tubes are cut or blocked to prevent the meeting of sperm and egg.
The illegal misuse of prenatal sex determination may lead to female foeticide. This contributes to an imbalance in the child sex ratio and is a serious social and ethical issue.
Rapid population growth increases pressure on resources such as food, water, housing, education and healthcare. It can make it difficult to improve the overall standard of living.
| Feature | Asexual Reproduction | Sexual Reproduction |
|---|---|---|
| Number of parents | Usually one | Usually two |
| Gametes | Not involved | Involved |
| Fertilisation | Absent | Present |
| Variation | Usually less variation | Greater variation |
| Speed | Generally faster | Generally slower |
| Examples | Fission, budding, fragmentation | Human reproduction, flowering plants |
Hereditary material that carries instructions for protein synthesis and body design.
Differences among individuals of the same species.
One parent divides into two daughter cells.
One parent produces many daughter cells.
Development of complete organisms from body fragments.
A new organism develops as an outgrowth from the parent.
New plants develop from roots, stems or leaves.
Transfer of pollen from anther to stigma.
Fusion of male and female gametes to form a zygote.
Tissue that exchanges nutrients, oxygen and wastes between mother and embryo.
Shedding of the uterine lining when fertilisation does not occur.
Methods used to prevent unwanted pregnancy.