Reproduction in Animals
1. Summary
- Male reproductive organs include a pair of testes, two sperm ducts, and a penis.Testes produce sperms, the male gametes. Sperms have a head, a middle piece and a tail. Sperms contain cell membrane, cytoplasm and nucleus.
- The female reproductive organs consist of a pair of ovaries, two oviducts also called fallopian tubes, and the uterus. The ovary produces female gametes called ova or eggs.
- When male and female gametes unite outside the body, it is called external fertilisation
- When fertilisation takes place inside the body, it is called internal fertilisation.
- When fertilisation takes place in a test tube, the offspring are called test tube babies.
- Fertilisation that takes place outside the human body is in-vitro fertilisation.
Reproduction is the biological process by which existing organisms give rise to their offspring. Reproduction can be of two types – Sexual mode and Asexual mode
Sexual mode of reproduction: This type of reproduction involves two organisms, the male and the female. Reproductive organs in humans produce gametes - eggs and sperms. A zygote, the future individual is formed by the fusion of an egg and a sperm.
Reproductive organs
Copulation is the act in which a male reproductive organ enters the female reproductive tract to discharge the male gametes.
Fertilisation is the fusion of male and female gametes to give rise to a single cell – zygote. Fertilisation can be external fertilisation or internal fertilisation.
Zygote, the super cell marks the beginning of a new individual. The zygote divides repeatedly to form a ball of cells making an embryo.
Embryo gets embedded in the wall of uterus, part of the female reproductive system. The development of the embryo takes place in the mother’s uterine wall. All parts of the body start developing in an embryo which finally transforms itself into foetus.
Reproduction in plants:
Stamens, the male reproductive organs give rise to male gametes, the pollen grains. Ovary, the female reproductive organ contains the female gametes, the ovules.
Pollination is the process in which pollen grains fall on to the stigma of the pistil.
Fertilisation is the process in which the male gamete fuses with the female gamete.
The nuclei of the pollen and that of ovule fuse to form a zygote. Fertilised ovules transform into seed
Reproduction In Animals
Modes of Reproduction
There are two modes by which animals reproduce. These are: (i) Sexual reproduction, and (ii) Asexual reproduction.
Sexual Reproduction
In
animals, males and females have different reproductive parts or organs.
Like plants, the reproductive parts in animals also produce gametes
that fuse to form a zygote. It is the zygote which develops into a new
individual. This type of reproduction beginning from the fusion of male
and female gametes is called sexual reproduction.
Male Reproductive Organs
The
male reproductive organs include a pair of testes (singular, testis),
two sperm ducts and a penis. The testis produces the male gametes called
sperms. Millions of sperms are produced by the testes. Though sperms
are very small in size, each has a head, a middle piece and a tail. Each
sperm is a single cell with all the usual cell components.
Female Reproductive Organs:
The
female reproductive organs are a pair of ovaries, oviducts (fallopian
tubes) and the uterus. Ovary produces female gametes called ova (eggs).
In human beings, a single matured egg is released into the oviduct by
one of the ovaries every month. Uterus is the part where development of
the baby takes place. Like the sperm, an egg is also a single cell.
Fertilization:
The
first step in the process of reproduction is the fusion of a sperm and
an ovum. When sperms come in contact with an egg, one of the sperms may
fuse with the egg. Such fusion of the egg and the sperm is called
fertilization. During fertilization, the nuclei of the sperm and the
egg fuse to form a single nucleus. This results in the formation of a
fertilized egg or zygote.
The
process of fertilization is the meeting of an egg cell from the mother
and a sperm cell from the father. So, the new individual inherits some
characteristics from the mother and some from the father.
Fertilization
which takes place inside the female body is called internal
fertilization. Internal fertilization occurs in many animals including
humans, cows, dogs and hens.
In many animals fertilization takes place outside the body of the female. In these animals, fertilization takes place in water.
During
spring or rainy season, frogs and toads move to ponds and slow flowing
streams. When the male and female come together in water, the female
lays hundreds of eggs. Unlike hen’s egg, frog’s egg is not covered by a
shell and it is comparatively very delicate. A layer of jelly holds the
eggs together and provides protection to the eggs.
As
the eggs are laid, the male deposits sperms over them. Each sperm swims
randomly in water with the help of its long tail. The sperms come in
contact with the eggs. This results in fertilization. This type of
fertilization in which the fusion of a male and a female gamete takes
place outside the body of the female is called external fertilization.
It is very common in aquatic animals such as fish, starfish, etc.
Development of Embryo
Fertilization
results in the formation of zygote which begins to develop 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. This developing structure is termed an embryo.
The embryo gets embedded in the wall of the uterus for further
development.
The
embryo continues to develop in the uterus. It gradually develops the
body parts such as hands, legs, head, eyes, ears, etc. The stage of the
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.
In
animals which undergo external fertilization, development of the embryo
takes place outside the female body. The embryos continue to grow
within their egg coverings. After the embryos develop, the eggs hatch.
Viviparous and Oviparous Animals
Some
animals give birth to young ones while some animals lay eggs which
later develop into young ones. The animals which give birth to young
ones are called viviparous animals. Those animals which lay eggs are
called oviparous animals.
Asexual Reproduction
This type of reproduction in which only a single parent is involved is called asexual reproduction.
In
each hydra, there may be one or more bulges. These bulges are the
developing new individuals and they are called buds. In hydra too the
new individuals develop as outgrowths from a single parent. Since new
individuals develop from the buds in hydra, this type of asexual
reproduction is called budding.
Another
method of asexual reproduction is observed in the microscopic organism,
amoeba. Amoeba is a single-celled organisms. It begins the process of
reproduction by the division of its nucleus into two nuclei. This is
followed by division of its body into two, each part receiving a
nucleus. Finally, two amoebae are produced from one parent amoeba. This
type of asexual reproduction in which an animal reproduces by dividing
into two individuals is called binary fission.
Summary
• There are two modes by which animals reproduce. These are: (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 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 fertilization. The fertilized egg is called a zygote.
•
Fertilization that takes place inside the female body is called
internal fertilization. This is observed in human beings and other
animals such as hens, cows and dogs.
•
Fertilization that takes place outside the female body is called
external fertilization. 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 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.
Reproduction in Animals
Solution of NCERT Exercise
Question: 1- Explain the importance of reproduction in organism.
Answer- Reproduction helps to complete the life cycle
of any species. Reproduction is essential for the continuation of a
species. It ensures the continuation of similar kind of individuals;
generation after generation. Reproduction is also responsible for
bringing variations in subsequent generations and ultimately evolution
of a new species.
Question: 2 - Describe the process of fertilization in human beings.
Answer- Fertilization- The fusion of male and female gametes is called fertilization.
In humans, internal fertilization occurs. During each
ovulation cycle, usually one egg is released from the ovary and is
transferred to the fallopian tube. The sperm travels to the fallopian
tube. Fertilization takes place in the fallopian tube.
Question: 3 - Choose the most appropriate answer. (a) Internal fertilization occurs
- In female body.
- Outside female body.
- In male body.
Answer -1. In female body.
(b) A tadpole develops into an adult frog by the process of- Fertilization
- Metamorphosis
- Embedding
- Budding
Answer- 2. Metamorphosis
(c) The number of nuclei present in a zygote. - None
- One
- Two
- Four
Answer-2. One
Question: 4- Indicate whether the following statements are true (T) or false(F): (a) Oviparous animals give birth to young ones.
Answer-(F)
(b) Each sperm is a single cell.
Answer (T)
(d) External fertilization takes place in frog.
Answer- (T)
(e) A new human individual develops from a cell called gamete.
Answer-(F)
(f) Egg laid after fertilization is made up of a single cell.
Answer- (T)
(g) Amoeba reproduces by budding.
Answer-(F)
(h) Fertilization is necessary even in asexual reproduction.
Answer-(F)
(i) Binary fission is a result of asexual reproduction.
Answer- (T)
(j) A zygote is formed as a result of fertilization.
Answer-(T)
(k) An embryo is made up of a single cell.
Answer- (F)
Question: 5 - Give two differences between a zygote and a foetus.
Answer
| Zygote | Foetus |
| The product of fusion of the nuclei of the sperm and egg is called zygote | The stage of the embryo which resembles a human being is called a foetus |
| It is a unicellular structure | It is a multicellular structure. |
Answer-The reproduction in which a single parent is
involved is called asexual reproduction. Budding and Binary fission are
the methods of asexual reproduction.
Budding -Hydra reproduces by budding. Many
bulges develop on the body of hydra. Each bulge grows into a new
individual. Bulges are called buds.
Binary fission -Amoeba reproduces by binary
fission. At first the nucleus divides into two nuclei and then the
mother cell divides into two; with each part receiving a nucleus.
Question: 7 - In which female reproductive organ does the embryo get embedded?
Answer- The embryo gets embedded in the wall of the uterus.
Question: 8 - What is metamorphosis? Give examples.
Answer- The transformation of the larva into adult
through drastic change is called metamorphosis. Metamorphosis can be
seen in many animals, e.g. frog and silkmoth. The tadpole stage of frog
is different from an adult frog. It metamorphoses into an adult frog.
The larva of silkmoth undergoes pupa stage and later on develops into a
moth.
Question: 9 - Differentiate between internal fertilization and external fertilization.
Answer:
| Internal fertilization | External fertilization |
| Takes place inside the body | Takes place out of the body |
| Less number of eggs is formed | A large number of eggs is formed |
| Examples: crocodile, bird, mammals | Examples: fish, frog |
Across
(1) The process of the fusion of the gametes.
Answer: Fertilization
(6)The type of fertilization in hen
Answer: Internal fertilization
(7)The term used for bulges observed on the sides of the body of hydra.
Answer: Bud
(8) Eggs are produce here.
Answer: Ovary
Down(2)sperms are produced in these male reproductive organs
Answer: Testis
(3)Another term for the fertilized egg.
Answer: Zygote
(4)These animals lay eggs.
Answer: Oviparous
(5)A type of fission in amoeba.
Answer: Binary fission
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