Reproduction in Animals | Class 8 Science | Chapter 9
Reproduction means making babies or offspring. It’s very important for keeping a species alive.
There are two ways animals and plants reproduce:
- This involves two parents, a male and a female. They have special parts that make tiny cells called gametes. These gametes join together to make a new baby with traits from both parents. Humans do this kind of reproduction.
- Only one parent is involved. They make a copy of themselves without any special cells from another parent. It’s like making a clone. Some simple creatures like amoebas and hydra do this.
Asexual Reproduction: One Parent Makes Copies
Asexual reproduction happens when only one parent is needed. There is no mixing of special information.
- For example, Hydra makes new beings from parts of itself. These new beings are like exact copies.
Sexual Reproduction: Two Parents Combine
Sexual reproduction needs a male and a female. They have special parts to make tiny cells. These cells join to make a baby with traits from both parents.
- Humans are an example of sexual reproduction. A baby gets traits from both its mom and dad.
Different Types of Asexual Reproduction
- Fission: One single-celled creature becomes two. The insides of the cell divide, and then the whole cell splits into two.
- Amoeba is a small creature that does this. It becomes two separate amoebas.
- Budding: A new creature grows on the parent and then breaks away to become independent.
- For example, yeast and hydra do this. A bud grows on them and then becomes its own creature.
The Importance of Cell Division
Reproduction happens with cell division. Cells split to make new cells. This is crucial for:
- Growing bigger
- Healing injuries
- Making new parts
- Creating special cells for reproduction
Two Types of Cell Division: Mitosis and Meiosis
- Mitosis: A single cell divides into two identical cells. This happens for growth and repair.
- Meiosis: One cell divides into four cells with half the usual number of parts. This is for making special cells used in reproduction.
How Humans Reproduce Sexually
- Male Reproductive System: Men have testes, sperm ducts, and a penis. Testes make tiny cells called sperm that can make babies.
- Female Reproductive System: Women have ovaries, fallopian tubes, and a uterus. Ovaries make tiny cells called eggs, or ova. These eggs can also make babies.
- Fertilization: When a sperm meets an egg, they join together. This is called fertilization. It makes a new cell called a zygote, which grows into a baby.
Remember, reproduction is how living things keep their species alive. Different creatures have different ways of making new life.
The importance of reproduction in organisms
- Reproduction is how living things have babies.
- It helps species keep going and more of them are born.
- Reproduction is essential for all life forms to survive.
Fertilization is when a tiny male cell and a tiny female cell come together to start making a baby.
- The male cells, called sperms, come from the man's private part.
- These sperms go into the woman's body through her private part.
- They travel through tubes in the woman's body called fallopian tubes.
- In the fallopian tubes, the sperms meet tiny female cells called eggs.
When a sperm meets an egg, they join together to make a special cell called a zygote. This is the beginning of a baby.
- The zygote starts dividing into more cells quickly.
- After a few days, it becomes a group of cells called a morula.
- About five days later, it becomes an embryo.
The embryo grows into a baby in the woman's uterus, which is like a special pouch inside her body.
Choose the most appropriate answer: (a) Internal fertilization occurs (i) in female body. (ii) outside female body. (iii) in male body. (iv) outside male body.
(i) in female body.
(b) A tadpole develops into an adult frog by the process of (i) fertilisation (ii) metamorphosis (iii) embedding (iv) budding
4. Indicate whether the following statements are True (T) or False (F). (a) Oviparous animals give birth to young ones. ( ) (b) Each sperm is a single cell. ( ) (c) External fertilisation takes place in the frog. ( ) (d) A new human individual develops from a cell called a gamete. ( ) (e) Egg laid after fertilisation is made up of a single cell. ( ) (f) Amoeba reproduces by budding. ( ) (g) Fertilisation is necessary even in asexual reproduction. ( ) (h) Binary fission is a method of asexual reproduction. ( ) (i) A zygote is formed as a result of fertilisation. ( ) (j) An embryo is made up of a single cell. ( )
- First stage of growth
- Created when male and female cells join
- Only one cell
- Splits to become an embryo
- Lasts around a week before changing
- Final stage of growth
- Shows body parts like a grown-up
- Comes after the embryo stage
- Grows inside the body
Sure, here's a simpler version:
Asexual Reproduction: Making Copies
Asexual reproduction is when a new organism is born from just one parent. No special cells from two parents are needed, so the number of chromosomes doesn't change.
Binary Fission in Amoeba: Splitting in Two
- Amoeba is a tiny creature with one cell.
- It divides into two parts, making two new amoebas.
- First, its nucleus divides into two. This is called karyokinesis.
- Then, the rest of the cell splits into two.
Budding in Hydra: Growing a New Self
- Hydra is another creature.
- It grows a small part on its body called a bud.
- The bud becomes like the parent and can break off to become its own creature.
These methods make new organisms without needing two parents.
In the female reproductive organ, the embryo gets attached to the uterus. This is where it grows and develops, forming body parts like legs, hands, eyes, and more. At this stage, the embryo is referred to as a fetus.
Metamorphosis is when an animal's body goes through big changes in structure and form. This usually involves cells growing and changing.
- Frogs: Frogs start as tadpoles with gills and tails. As they grow, they go through metamorphosis. Their bodies change, they lose their tails and develop lungs for breathing air. Eventually, they become mature frogs.
- Insects: Many insects, like butterflies and beetles, go through metamorphosis. They start as eggs, then become larvae or caterpillars. After some time, they go into a pupal stage, where they transform completely. Finally, they emerge as adults with wings and different body parts.
Metamorphosis helps animals adapt to different stages of their lives and environments.
Comparison between internal fertilisation and external fertilisation:
- Happens inside the female's body.
- Offspring have higher chances of survival.
- Protects the embryo from harsh conditions.
- Examples include humans, dogs, cows, and monkeys.
- Occurs outside the female's body.
- Offspring have lower chances of survival.
- Often used by aquatic animals.
- Produces many offspring to compensate for risks.
- Examples include fish, frogs, and certain organisms.
In internal fertilisation, the joining of the egg and sperm happens inside the female, leading to better protection and survival for the developing embryo. In external fertilisation, the egg and sperm come together outside the female's body, and although it can produce a large number of offspring, their survival is generally lower due to exposure to the environment.