Class 8 Unit-5 (Life Processes)

 

Unit-5 (Life Processes)

Life processes are the essential functions that living organisms perform to maintain life, ensuring survival, growth, and reproduction.

 

Reproduction

Reproduction is the biological process by which living organisms produce new individuals of their own kind. Reproduction is an essential and internal quality of every organism through which they are continuing their generation.

 

Importance of Reproduction

·   Reproduction helps living things to make babies and continue their generation.

·   It stops animals and plants from disappearing from the world.

·   It allows parents to pass their traits to their children.

·   Sexual reproduction creates differences in children, which helps them survive in nature.

 

Types of reproduction:

There are two main types of reproduction:

1.   Asexual Reproduction in plants and animals:

In this type, a single parent produces children without the involvement of sex cells. The children are usually identical to the parent. Example: Amoeba, Hydra, bacteria.

There are different modes of asexual reproduction occurring in plants and animals. These are as follows:

i. Fission

The mode of asexual reproduction in which the living organism divides into two or more than two individuals is called fission. There are two types of fission:

a. Binary Fission: The organism splits into two equal parts. Example: Amoeba, bacteria.

b. Multiple Fission: The organism divides into many parts at the same time, forming many new organisms. Example: Plasmodium.

 

ii. Budding: A small part of the parent grows into a new organism. Example: Hydra, yeast.

iii. Fragmentation & regeneration: The body of an organism breaks into pieces, and each piece grows into a new organism. Example: Spirogyra, Planaria.

iv. Sporulation: Tiny spores are produced that grow into new organisms. Example: Fungi like bread mold.

v. Propagation: New plants grow from roots, stems, or leaves of the parent plant. Example: Potato, ginger.

 

Advantages of asexual reproduction

a. Only one parent is needed to produce children.

b. It is a fast way to make many children.

c. Children are usually strong and similar to the parent.

d. It does not need a mate, so it can happen anytime.

 

Disadvantages of asexual reproduction

a. Only one parent is involved, so there is no variation in children.

b. Children are identical, so if disease affects one, all can be affected.

c. It is difficult for species to adapt to changing environments.

 

 

 

2.   Sexual Reproduction

In this type, two parents (male and female) are involved, and the children are produced by the fusion of male and female sex cells. Example: Humans, plants, animals.

 

Characteristics of sexual reproduction

a. Two parents (male and female) are involved.

b. Male and female gametes (sperm and egg) fuse during fertilization.

c. Offspring are genetically different from their parents.

d. It creates variation in the species.

e. It usually takes more time than asexual reproduction.

 

Sexual reproduction in animals:

a. Sexual reproduction in animals happens when two parents (male and female) are involved.

b. The male produces sperm and the female produces egg (ovum).

c. Fertilization occurs when the sperm and egg join to form a zygote.

d. The zygote develops into a new animal.

e. Examples of animals that reproduce sexually are humans, birds, and fish.

 

Fertilization

Fertilization is the process where the sperm and egg join to form a zygote.

Fertilization can be of two types:

1. Internal Fertilization: Sperm joins the egg inside the female’s body. Example: Humans, birds, reptiles.

2. External Fertilization: Sperm joins the egg outside the female’s body, usually in water. Example: Fish, frogs.

 

Sexual reproduction in plants:

a. Sexual reproduction in plants needs two gametes – male and female.

b. Pollen is the male gamete and ovule is the female gamete.

c. When pollen joins the ovule, fertilization happens and forms a zygote.

d. The zygote grows into a new plant.

e. Example: Pea, hibiscus, sunflower.

 

Pollination in plant

Pollination is the process of transferring pollen from the male part (anther) to the female part (stigma) of a flower.

-It helps in fertilization so that seeds can form.

-Pollination can happen in two ways:

1. Self-Pollination: Pollen goes to the stigma of the same flower. Example: Pea.
2. Cross-Pollination: Pollen goes to the stigma of a different flower of the same species. Example: Sunflower.

 

Fertilization in plant

Fertilization is the process where the male gamete (pollen) joins with the female gamete (ovule) to form a zygote, which grows into a new plant.

-Fertilization usually happens after pollination, when pollen reaches the stigma of a flower.

 

 

 

Seed

-A seed is the small part of a plant that can grow into a

 new plant.

-It is formed after fertilization in plants.

 

Types of plants based on cotyledon

1. Monocotyledon (Monocot): A monocotyledon is a plant that has only one seed leaf (cotyledon) in its seed.

Examples: Rice, wheat, maize (corn), banana, onion, grass, etc.

 

2. Dicotyledon (Dicot): A dicotyledon is a plant that has two seed leaves (cotyledons) in its seed.

Examples: Bean, pea, mango, mustard, rose, sunflower, etc.

 

-A seed has three main parts:

1. Seed coat – the outer cover that protects the seed.
2. Endosperm– the food-storage tissue inside a seed.
3. Embryo – the baby plant inside the seed.

 

Functions of seed

·   A seed helps in the reproduction of plants.

·   It protects the baby plant (embryo) inside.

·   It stores food for the growth of the baby plant.

·   It allows plants to survive in harsh conditions and grow when conditions are right.

·   Seeds help in the spread (dispersal) of plants to new places.

 

 

Dispersal of seed

Seed dispersal means the spreading of seeds from the parent plant to new places.

-Seeds are dispersed in different ways:

1. By Wind: Light seeds with wings or hair fly with air. Example: Cotton, dandelion.

2. By Water: Seeds that can float move with water. Example: Coconut, lotus.

3. By Animals: Animals eat fruits and drop seeds or carry them on their bodies. Example: Mango, berries.

4. By Explosion: Some fruits burst and throw seeds away. Example: Pea, balsam.

 

Germination of seed

-Germination is the process by which a seed grows

  into a new plant.

-It starts when the seed gets water, air, and warmth.

-The seed coat breaks, a root grows downward, and a

  shoot grows upward.

-The necessary conditions for germination of seed

a. Water and moisture

b. Air

c. Soil

d. Sunlight

e. Temperature