Here’s the whole chapter in very simple words.
Reproduction means making new organisms, like parents having babies or a plant making new plants.
An organism does not need reproduction to stay alive, but reproduction helps its kind continue to exist.
Example: One dog can live alone, but dogs as a group need to make puppies so dogs do not disappear.
DNA is like an organism’s instruction book.
It tells the body how to grow and work. When an organism reproduces, it makes a copy of this instruction book and gives it to the new organism.
The copy is usually very similar, but tiny mistakes can happen. These small differences are called variations.
Variation means that members of the same species are a little different.
Imagine many bacteria living in warm water. If the water becomes very hot, most may die, but a few heat-resistant bacteria may survive.
So, variation can help a species survive changes in its surroundings.
Asexual reproduction means one parent makes new organisms.
The new organisms are usually very similar to the parent.
Examples include:
Fission
Fragmentation
Regeneration
Budding
Vegetative propagation
Spore formation
Fission means splitting into pieces.
A single-celled organism copies its DNA and divides into new cells.
One cell divides into two cells.
Example: Amoeba and many bacteria.
One cell divides into many cells at the same time.
Example: Plasmodium, the organism that causes malaria.
In budding, a small bump grows on the parent’s body.
The bump gets bigger, becomes a new organism, and then separates.
Example: Yeast and Hydra.
It is like a tiny baby growing on the side of its parent.
Fragmentation means breaking into pieces.
Each piece can grow into a complete organism.
Example: Spirogyra, a green thread-like alga, breaks into smaller pieces. Each piece grows into a new Spirogyra.
Regeneration means growing missing body parts.
Some simple animals can grow into complete organisms from their body pieces.
Examples: Planaria and Hydra.
If a Planaria is cut into pieces, each piece may grow into a complete Planaria.
Regeneration is usually a repair ability, although it can sometimes produce new organisms.
Vegetative propagation means growing a new plant from a root, stem, or leaf instead of from a seed.
Examples:
Potato grows from buds, called eyes.
Bryophyllum grows from buds on its leaves.
Sugarcane grows from pieces of stem.
Money plants grow from stem pieces.
Advantages:
New plants grow quickly.
They are very similar to the parent plant.
Some plants that do not make seeds can still be grown.
Some organisms make tiny cells called spores.
Spores have strong protective coverings. When they land in a moist place, they can grow into new organisms.
Example: Bread mould, or Rhizopus.
Spores are useful because they are small, light, and can spread through the air.
Sexual reproduction usually involves two parents.
One parent provides a male germ-cell, and the other provides a female germ-cell.
These two cells join together and make a new cell called a zygote.
The zygote grows into a new organism.
Sexual reproduction mixes information from two parents.
This creates more variation in the children.
For example, a child may have the mother’s eyes, the father’s hair, and a mixture of other features.
This variation can help organisms survive changing environments.
Germ-cells are special reproductive cells.
Examples:
Sperm in males
Eggs in females
Pollen cells in flowering plants
These cells have half the usual number of chromosomes. This happens through a special type of cell division called meiosis.
When a sperm and egg join, the normal chromosome number is restored.
The flower is the plant’s reproductive part.
The stamen is the male part.
It produces pollen grains, which carry the male reproductive cell.
The stamen has:
Anther
Filament
The pistil is the female part.
It contains:
Stigma
Style
Ovary
The ovary contains ovules, which contain female reproductive cells.
Pollination means moving pollen to the stigma.
Pollen moves to the stigma of the same flower or the same plant.
Pollen moves from one plant to another plant.
Wind, water, insects, birds, and other animals can carry pollen.
After pollen lands on the stigma, it grows a tube down toward the ovary.
The male cell travels through this tube and joins the female cell inside an ovule.
This joining is called fertilisation.
The fertilised cell becomes a zygote.
Then:
The zygote becomes an embryo.
The ovule becomes a seed.
The ovary becomes a fruit.
A seed is like a tiny plant packed inside a protective case.
It needs:
Water
Air
Suitable warmth
Then it begins to grow.
The radicle becomes the root, and the plumule becomes the shoot.
Puberty is the time when a child’s body begins changing into an adult body.
During puberty:
The body grows quickly.
Hair grows in new places.
Skin may become oily.
Boys’ voices may deepen.
Girls’ breasts develop.
Girls begin menstruation.
Reproductive organs become mature.
These changes happen gradually and at different ages for different people.
The male reproductive system makes and carries sperm.
Important parts include:
Testes: make sperm and testosterone.
Scrotum: holds the testes outside the body.
Vas deferens: carries sperm.
Seminal vesicles and prostate gland: add liquid and nutrients to sperm.
Urethra: carries sperm out of the body.
Penis: helps transfer sperm.
The female reproductive system makes eggs and supports the developing baby.
Important parts include:
Ovaries: make eggs.
Fallopian tubes: carry eggs and are usually where fertilisation happens.
Uterus: where the embryo grows.
Cervix: opening between the uterus and vagina.
Vagina: passage through which sperm enters and a baby can leave the body.
During sexual reproduction, sperm may meet an egg in the fallopian tube.
The sperm and egg join to form a zygote.
The zygote divides and becomes an embryo.
The embryo attaches to the wall of the uterus and grows into a baby.
The embryo needs food and oxygen while it grows.
The placenta acts like a helpful connection between the mother and embryo.
It allows:
Food to reach the embryo.
Oxygen to reach the embryo.
Waste materials to leave the embryo.
The mother’s blood and the embryo’s blood usually do not mix directly.
Every month, the uterus prepares a soft, blood-rich lining in case an embryo arrives.
If the egg is not fertilised, the lining is not needed.
It leaves the body as blood and mucus through the vagina.
This is called menstruation.
Reproductive health means keeping the reproductive system healthy and making safe, informed choices.
Sexually transmitted diseases can spread through sexual contact.
Examples include:
Gonorrhoea
Syphilis
HIV/AIDS
Some viral infections
Condoms can help reduce the risk of many sexually transmitted infections.
Contraception means preventing pregnancy.
Methods include:
Condoms: stop sperm from reaching the egg and help reduce infection risk.
Oral pills: prevent the release of eggs.
Copper-T: placed inside the uterus.
Vasectomy: blocks the sperm-carrying tube in males.
Tubectomy: blocks the fallopian tubes in females.
A Copper-T helps prevent pregnancy, but it does not protect against sexually transmitted infections.
Asexual reproduction | Sexual reproduction |
|---|---|
One parent | Usually two parents |
No joining of sperm and egg | Sperm and egg join |
Children are very similar to parent | Children have a mixture of features |
Usually faster | Usually more complex |
Less variation | More variation |
Organisms reproduce by making new individuals, either from one parent through simple methods or from two parents through sexual reproduction, and DNA copying creates similarities and differences in living things.