REPRODUCTION IN ANIMALS

IMPORTANT TERMS

Reproduction              Reproduction may be defined as the process by which living things produce offspring of their own kind.

Asexual Reproduction   In asexual reproduction, a new individual is formed from the cell(s) of a single parent. For example- Amoeba, Hydra, Yeast, Starfish etc.

Sexual Reproduction    In sexual reproduction, two parents are required to produce new individual. For example- Most plants and mammals including human being.

Fertilization                  The Fusion of male and female gametes to produce a new organism is known as fertilization.

Internal Fertilization      In this type of fertilization, the fusion of male and female gametes occurs inside the female’s body. For example- Mammals such as cow, horse, dog, cat and human being.

 

External Fertilization    In this type of fertilization, the fusion of male and female gametes occurs outside the female’s body. For example- Fish, frog and starfish.

 

Viviparous Animals      Animals that give birth to live offspring are known as viviparous animals. For example- Mammals such as cow, dog, horse, cat including human being etc.

 

Oviparous Animals      Animals that lay eggs, which hatch into offspring are called as oviparous animals. For example- Birds, snakes, frogs etc.

 

Metamorphosis           The transformation of larva into adult through a series of drastic changes is called metamorphosis.

 

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Reproduction

Reproduction is defined as the process by which living things produce offspring of their own kind.

Modes of Reproduction

There are two types of modes for reproduction.

  • Asexual reproduction
  • Sexual reproduction

 

 

 

Asexual reproduction- In this type of reproduction, a new individual is formed from the cell(s) of a single parent. Amoeba, Hydra, Yeast, Starfish, Sponges and worms reproduce asexually. Examples of asexual reproduction are Budding and Binary Fission

 

  • Binary Fission- Amoeba reproduces by binary fission.

 

                   

In binary fission of Amoeba, Nucleus first divides into two nucleus and then body divides into two parts, each part receiving one nucleus. Hence two daughter Amoeba are formed.

Cells exist in different shapes. They can be disc-shaped, polygon, rectangular, branched or even irregular. The shape of cell depends on the specific function it performs.

  • Budding- Hydra reproduces by Budding.

 

 

 

In hydra, a bulge known as bud, is formed.

The Bud grows to form a baby Hydra.

Then the baby Hydra separates from the parent.

Sexual reproduction- In this type of reproduction, two parents are required to produce a new organism. All plants and mammals, including human beings, reproduce sexually. Example of sexual reproduction is reproduction in Human Beings.

Both Males and Females have special reproductive cells called as gametes. The female gamete is known as ovum and the male gamete is known as sperm. Two gametes join or fuse during a process called fertilization. This initiates the formation of a baby.

The Zygote gradually develops into an Embryo. The zygote divides repeatedly to give rise to a ball of cells. The cells then begin to form groups that develop into different tissues and organs of the body. The developing structure is called an Embryo. The Embryo gets embedded in the wall of the uterus. The development continues and the stage of an embryo in which all the body parts can be identified is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby. It takes 40 weeks for the child to be born.

Male Reproductive Organs

The male reproductive organs include a pair of Testes, Urethra, Two sperm duct and Penis.

 

 

 

  • Testis- Testis is an endocrine gland. There are two testes in a male body. It is made up of numerous coiled tubes that produce sperm cells. When a male reaches puberty, the testes starts producing male sex hormones Testosterone.
  • Sperm Duct- Sperm duct is a narrow tube that helps to transport sperms produced in the testes. Several fluids are secreted inside the tube by different glands, which mix with the sperm to form a fluid called semen.
  • Penis- Penis transfers the semen with the sperms into the female’s body.
  • Urethra- Urethra is a tube inside the penis through which semen and urine passes out of the body.

Female Reproductive Organs

             Female reproductive organs includes Ovary, Oviducts, Uterus and Vagina

  • Ovary- Ovary is an endocrine gland. There are two ovaries in a female’s body. Each ovary has a shape and size almost that of almond. When a girl reaches puberty, the ovary starts producing female sex hormones Oestrogen.
  • Oviducts- Oviduct also known as Fallopian Tube, which carries the ovum released by the ovary for the fertilization.
  • Uterus- Uterus is the organ where zygote matures and grows till it is ready to be born. The Embryo develops and grows inside the uterus which is also called Womb.
  • Vagina- Vagina receives the penis during Sexual intercourse.

                                                                                               

Fertilization

The fusion of male and female gametes to produce new organisms is called fertilization. The main stages of fertilization in human being are as follows.

 

  1. Once a month, an ovum is released from ovary by the process called Ovulation.
  2. The ovum moves into the oviduct.
  3. During sexual intercourse, the male transfer sperms in the vagina through the penis. The sperms travel through a narrow opening called cervix into the uterus and then to the oviduct. A single sperm fuses with the ovum and the fertilization takes place.
  4. The fertilized ovum continues its journey down the oviduct, into the uterus. The fertilized ovum implants itself into the uterus wall and develops into a human embryo.

Types of Fertilization

There are two types of fertilization- Internal fertilization and External fertilization

 

Internal Fertilization- In this type of fertilization, the fusion of male and female gametes occurs inside the female’s body. Mammals such as cow, horse, dog, cat buffalo and human beings etc. reproduce by internal fertilization.

External Fertilization- In this type of fertilization, the fusion of male and female gametes occurs outside the body. Fish, frog, starfish etc. are the examples of external fertilization.

During spring or rainy season the female lays hundreds of eggs. Males deposits sperms over them. Each sperm swims randomly in water with the help of its long tail. The sperm comes in contact with the eggs. This results in fertilization known as External fertilization.

Viviparous and Oviparous Animals

Viviparous Animals- Animals that give birth to the live offspring i.e. baby, are called as Viviparous animals. Mammals such as cow, dog, cat and human being all are the examples of viviparous animals.

 

Oviparous Animals- Animals that lay eggs, which hatch into the offspring, are called as Oviparous animals. Birds, snakes, frogs, fish etc. are the examples of Oviparous animals.

Determination of the Sex of the Baby

The thread like structures found inside the nucleus is called chromosomes, which carry information in the form of genes.

 

Each cell contains 23 pairs of chromosomes, in which 22 pairs are called autosomes which are similar in males and females and one pair of chromosomes is sex chromosome. There are two types of sex chromosomes X and Y chromosomes. Female cell contains the XX pair and the male contains XY pair.

 

The gametes contain only one set of chromosomes consisting of one member of each pair. Ovum consists of one chromosome X while sperm may contain X or Y.

 

When the ovum containing X gets fertilized with sperm containing X, then the pair of sex chromosome will be XX and the baby will be a girl. If the ovum gets fertilized by a sperm containing Y chromosome, then the sex chromosomes pair will be XY and the baby will be boy.

 

Metamorphosis

The transformation of larva into adult through series of drastic changes is called Metamorphosis.

Metamorphosis occurs in Frogs and Butterflies

There are three main stages in the life cycle of the frog

Egg- Larva- Adult. These changes are controlled by the hormone Thyroxine.

 

 

 

 

Similarly, there are four main stages in the life cycle of Butterfly.

Egg- Larva- Pupa- Adult. These changes are controlled by two hormones- Juvenile hormone and Ecdysone.

 

Gender Issues and Myths

 

Techniques such as ultrasound, which enable doctors to determine the sex of the unborn child, were being misused by the people for killing the girl foetus inside the mother womb, which is called Abortion.

 

To put a stop to female infanticide (killing of girl foetus), the government has made it illegal to find out the sex of the foetus.

 

Many people blame the mother for the birth of a girl child. Such thinking is scientifically baseless, as the sex of the child is determined by the sperm of the father.

      

Cloning- It is the production of the exact copy of a cell, any other living part, or a complete organism. Cloning of an animal is done successfully for the first time by Ian Wilmut and his colleagues. They successfully cloned a sheep named Dolly. Dolly was born on 5th july1996 and died on 14th February due to lung disease.

Some Interesting Facts

  • During pregnancy, uterus expands its capacity to 500 times its normal capacity.
  • Some Women are born with two uterus.
  • In recent studies, it was determined that men with higher pitched voices have more sperms.
  • The Ancient Egyptians used contraceptives to prevent unwanted babies. They used honey or crocodile dung as contraceptives.
  • Vagina of women is acidic, averaging about 4.5 on pH scale i.e. as acidic as tomatoes.
  • In human body, Chromosome 1, which is the non-sex chromosome and are basic units of information for DNA, is found to be the biggest containing around 10 billion atoms.
  • Liver has an amazing ability to grow back if a part of it is removed due to injury or some disease or surgery to the right size as it was.