Reproduction in Animals

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Reproduction in Animals
Modes of Reproduction
Sexual Reproduction
Male Reproductive Organs
Female Reproductive Organs
Fertilisation
Development of Embryo
Asexual Reproduction
Chapter Summary:
KEYWORDS

Introduction

Remember digestion, circulation, and respiration? These processes are crucial for survival.
Reproduction is vital for the continuation of a species.
Without reproduction, species would not continue.

Modes of Reproduction

There are two modes of reproduction in animals:
1. Sexual Reproduction
2. Asexual Reproduction

Sexual Reproduction

Plants and animals reproduce sexually with male and female parts.
Reproductive parts produce gametes (sperms and eggs) that fuse to form a zygote.
The zygote develops into a new individual.

Male Reproductive Organs

Includes: testes, sperm ducts, and penis.
Testes produce millions of sperms.
Sperm structure: head, middle piece, and tail.

Female Reproductive Organs

Includes: ovaries, oviducts (fallopian tubes), and uterus.
Ovaries produce eggs (ova).
One egg is released into the oviduct every month.
Uterus is where the baby develops.
Eggs vary in size; ostrich eggs are the largest.

Interesting Fact

The size of animal eggs varies widely. For example:
- Humans have small eggs.
- Hens have larger eggs.
- Ostrich eggs are the largest!

Fertilisation

What is Fertilisation?

The first step in reproduction.
Fusion of a sperm and an ovum (egg).
When a sperm meets an egg, they fuse to form a fertilised egg called a zygote.
The zygote is the start of a new individual.

Characteristics Inheritance

The new individual inherits traits from both parents.
Look at your siblings to see similarities with your parents.

Internal Fertilisation

Takes place inside the female body.
Common in humans, cows, dogs, and hens.

External Fertilisation

Happens outside the female body, usually in water.
Common in aquatic animals like fish and starfish.
Example: Frogs and toads lay eggs in water; males deposit sperms over the eggs to fertilise them.

Interesting Facts

Test Tube Babies: In some cases, fertilisation occurs outside the body (IVF). Doctors collect eggs and sperms, fertilise them outside, then place the zygote in the uterus. These babies are called test-tube babies.
Egg Laying: Fish and frogs lay hundreds of eggs because many don’t get fertilised due to environmental factors. Hens lay one egg at a time with a better chance of development.

Development of Embryo

Formation of Embryo

Zygote Formation: Fertilisation creates a zygote.
Cell Division: The zygote divides into a ball of cells.
Tissue and Organ Development: Cells form groups that become tissues and organs.
Embryo Embedding: The embryo embeds in the uterus wall for further development.

Embryo to Foetus

Development: The embryo develops body parts like hands, legs, head, eyes, and ears.
Foetus Stage: When body parts are identifiable, it’s called a foetus.
Birth: After full development, the mother gives birth to the baby.

Hens and Eggs

Internal Fertilisation: Hens have internal fertilisation.
Egg Formation: The zygote travels down the oviduct, forming protective layers, including a hard shell.
Development Inside Egg: The hen provides warmth for about 3 weeks until the chick develops and hatches.

External Fertilisation

Outside Female Body: Embryo development happens outside the female body.
Egg Hatching: Embryos grow within egg coverings and hatch. Example: tadpoles in ponds.

Viviparous and Oviparous Animals

Viviparous: Animals that give birth to young ones (e.g., dogs, cows, cats).
Oviparous: Animals that lay eggs (e.g., hens, frogs).

Young Ones to Adults

Growth: New individuals grow until they become adults.
Different Appearances: Young ones may look very different from adults. Example: frog life cycle (egg → tadpole → adult).
Metamorphosis: Drastic changes from larva to adult are called metamorphosis. Example: tadpoles to frogs.
Human Growth: Humans do not undergo metamorphosis; they have similar body parts from birth.

Asexual Reproduction

Introduction

We learned about reproduction in familiar animals, but what about tiny animals like hydra and amoeba? Let’s find out.

Budding in Hydra

Hydra can have one or more bulges called buds.
Buds develop into new individuals from a single parent.
This type of reproduction with only one parent is called asexual reproduction.
In hydra, it’s specifically called budding.

Binary Fission in Amoeba

Amoeba is a single-celled organism.
The nucleus of the amoeba divides into two.
The body then splits into two, each with a nucleus.
This process creates two amoebae from one parent.
This type of asexual reproduction is called binary fission.

Other Methods of Asexual Reproduction

There are more methods where a single parent reproduces young ones.
These will be studied in higher classes.

Interesting Fact: Cloning

Cloning creates an exact copy of a cell, part, or entire organism.
The first successful animal clone was Dolly the sheep, cloned by Ian Wilmut and colleagues.
Dolly was born on July 5, 1996, and was identical to the sheep from which the cell was taken.
Dolly died on February 14, 2003, due to lung disease.
Cloning often results in severe abnormalities, and many clones do not survive long.

Chapter Summary:

There are two modes by which animals reproduce: (i) Sexual reproduction, and (ii) Asexual reproduction.
Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.
The reproductive organs in the female include ovaries, oviducts, and uterus.
The reproductive organs in the male include testes, sperm ducts, and penis.
The ovary produces female gametes called ova, and the testes produce male gametes called sperms.
The fusion of ovum and sperm is called fertilisation. The fertilised egg is called a zygote.
Fertilisation that takes place inside the female body is called internal fertilisation. This is observed in human beings and other animals such as hens, cows, and dogs.
Fertilisation that takes place outside the female body is called external fertilisation. This is observed in frogs, fish, starfish, etc.
The zygote divides repeatedly to give rise to an embryo.
The embryo gets embedded in the wall of the uterus for further development.
The stage of the embryo in which all the body parts are identifiable is called foetus.
Animals such as human beings, cows, and dogs which give birth to young ones are called viviparous animals.
Animals such as hen, frog, lizard, and butterfly which lay eggs are called oviparous animals.
The transformation of the larva into an adult through drastic changes is called metamorphosis.
The type of reproduction in which only a single parent is involved is called asexual reproduction.
In hydra, new individuals develop from buds. This method of asexual reproduction is called budding.
Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.