1. Reproduction-
ü It is one of the important life process.
ü It ensures the continuation of similar kinds of individuals generation after generation.
ü There are two modes by which animals reproduce viz- Sexual reproduction and Asexual reproduction.
ü Sexual Reproduction- Involves two individuals. One male and one female.
ü Male reproductive organs are a pair of testes, sperm ducts, and a penis. The female reproductive organs are a pair of ovaries, oviducts and the uterus.
ü Testes in male produces sperms. They pass through sperm duct and are released through penis.
ü Ovary produces females gametes called ova. In human beings, a single matured egg is released into the oviduct by one of the ovaries every month.
ü Uterus is the part of the female reproductive system where the development of the embryo takes place.
ü Both sperm and ova are single-celled structure.
Figure 01- Male reproductive organ and human sperm
Figure 02- Female reproductive organ and human egg (ova)
2. Fertilization-
ü The fusion of male and female gamete i.e the fusion of sperm and ova is called as fertilization.
ü During fertilization, the nuclei of the sperm (n) and the egg (n) are fused to form a single nucleus (2n).
ü As result of fertilization zygote is formed.
ü Based on where fusion takes place, fertilization is of two types viz- internal and external.
ü Fertilization which takes place inside the female body is called internal fertilization.
ü Fertilization which takes place outside the body of the female is called external fertilization.
Figure 03- Fertilization and zygote formation
3. Post Fertilization Events-
ü The zygote divides repeatedly to give rise to a spherical mass of cells.
ü The cells then begin to differentiate into various tissues.
ü This developing structure is called an embryo.
ü Zygote formation and development of an embryo from the zygote.
ü Spherical mass of cells is enlarged.
ü Embedding of the embryo in the uterus occur.
ü The embryo gets implanted within the wall of the uterus, i.e. endometrium for further development.
ü The stage of the embryo in which all the body parts are identifiable is called a foetus.
ü The animals which give birth to young ones are called viviparous animals.
ü The animals which lay eggs are called oviparous animals.
ü The transformation of larva into an adult through drastic changes is called metamorphosis.
Note: Animals such as human beings, cows and dogs which give birth to the young ones are called Viviparous animals. Animals such as hen, frog and butterfly which lay eggs are called oviparous animals.
Figure 04- Post fertilization events
4. Asexual Reproduction-
ü The type of reproduction in which only a single parent is involved, is called asexual reproduction.
Figure 05- Budding in hydra
ü Budding- In small animals like a hydra, new individuals develop from buds. This method of asexual reproduction is called budding. In this type of reproduction, a lateral bud arises from the body’ of the parent organism, it matures and gets detached from the body to behave as a new organism. A bud is lateral outgrowth from the parent body that assumes the shape of parent. It ultimately gets detached and behaves as a new individual.
Figure 06- Binary fusion in amoeba
ü Binary Fission- In binary fission, a single-celled individual reproduces by dividing itself into two. For example in case of Amoeba. Amoeba a single-celled organism, reproduces by simply dividing itself into two daughter cells. This type of asexual reproduction is called Binary fission.
5. Reproduction In Frogs-
ü Frogs reproduce my means of sexual reproduction involving a male and a female individual.
ü External fertilization occurs. Male lay out sperms in open water, whereas female lay out egg/ove in open water.
ü Fusion occurs externally and results in formation of zygote that turns into tadpole.
ü In the life process of a frog, we find three distinct stages, that is-
egg → tadpole → adult
ü These tadpoles get transformed into adults which are capable of jumping and swimming, and are finally transformed into frog.
ü The drastic change which transforms a larva into an adult in case of frog is called metamorphosis.
6. Cloning-
ü Cloning is the creation of an organism that is an exact genetic copy of another.
ü This means that every single bit of DNA is the same between the two organisms.
NCERT PRACTICE QUESTIONS
1. Explain the importance of reproduction in organisms.
Ans.- Importance of reproduction in organisms is as follows- Reproduction is meant for the survival of all living things. Reproduction is termed to be a biological process in which organisms give birth to their off springs. It helps in maintaining the continuity of a particular race and helps in increasing the population of the species.
2. Describe the process of fertilization in human beings.
ü Fertilization is defined as the process in which there is a fusion of male gamete and female gamete.
ü The male gametes or sperms are released from the male reproductive organ called the penis. The sperms release and enter the female body through the vagina.
ü From the vagina, sperms travel through the fallopian tubes where they meet the eggs. From there on, the process of fertilization takes place in the fallopian tube.
ü The male gamete cell (sperm) and female gamete cell (egg) fuse together to form a zygote.
ü The zygote divides rapidly to form a group of cells called morula, which becomes the embryo after approximately five days.
ü The foetus is present for about eight weeks after the fertilization.
3. 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.
(b) A tadpole develops into an adult frog by the process of
(i) fertilization (ii) metamorphosis (iii) embedding (iv) budding
(c) The number of nuclei present in a zygote is
(i) none (ii) one (iii) two (iv) four
Ans.- a) (i) in female body. b) (ii) metamorphosis c) (iii) two
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 frog. ( )
(d) A new human individual develops from a cell called 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. ( )
Ans.- a) False b) True c) True d) False e) True f) False g) False h) True i) True j) False
5. Give two differences between a zygote and a foetus.
6. Define asexual reproduction. Describe two methods of asexual reproduction in animals.
Ans.- The type of reproduction in which only a single parent is involved, is called asexual reproduction.
Budding in hydra
Budding- In small animals like a hydra, new individuals develop from buds. This method of asexual reproduction is called budding. In this type of reproduction, a lateral bud arises from the body’ of the parent organism, it matures and gets detached from the body to behave as a new organism. A bud is lateral outgrowth from the parent body that assumes the shape of parent. It ultimately gets detached and behaves as a new individual.
Binary fusion in amoeba
Binary Fission- In binary fission, a single-celled individual reproduces by dividing itself into two. For example in case of Amoeba. Amoeba a single-celled organism, reproduces by simply dividing itself into two daughter cells. This type of asexual reproduction is called Binary fission.
7. In which female reproductive organ does the embryo get embedded?
Ans.-
ü The zygote divides repeatedly to give rise to a spherical mass of cells.
ü The cells then begin to differentiate into various tissues.
ü This developing structure is called an embryo.
ü Zygote formation and development of an embryo from the zygote.
ü Spherical mass of cells is enlarged.
ü Embedding of the embryo in the uterus occur.
ü The embryo gets implanted within the wall of the uterus, i.e. endometrium for further development.
ü The stage of the embryo in which all the body parts are identifiable is called a foetus.
ü The animals which give birth to young ones are called viviparous animals.
ü The animals which lay eggs are called oviparous animals.
ü The transformation of larva into an adult through drastic changes is called metamorphosis.
8. What is metamorphosis? Give examples.
Ans.-
ü Frogs reproduce my means of sexual reproduction involving a male and a female individual.
ü External fertilization occurs. Male lay out sperms in open water, whereas female lay out egg/ove in open water.
ü Fusion occurs externally and results in formation of zygote that turns into tadpole.
ü In the life process of a frog, we find three distinct stages, that is-
egg → tadpole → adult
ü These tadpoles get transformed into adults which are capable of jumping and swimming, and are finally transformed into frog.
ü The drastic change which transforms a larva into an adult in case of frog is called metamorphosis.
9. Differentiate between internal fertilization and external fertilization.
Ans.-
ü The fusion of male and female gamete i.e the fusion of sperm and ova is called as fertilization.
ü During fertilization, the nuclei of the sperm (n) and the egg (n) are fused to form a single nucleus (2n).
ü As result of fertilization zygote is formed.
ü Based on where fusion takes place, fertilization is of two types viz- internal and external.
ü Fertilization which takes place inside the female body is called internal fertilization.
ü Fertilization which takes place outside the body of the female is called external fertilization.
10. Complete the crossword puzzle using the hints given below.
Across
1. The process of the fusion of the gametes.
6. The type of fertilization in hen.
7. The term used for bulges observed on the sides of the body of hydra.
8. Eggs are produced here.
Down
2. Sperms are produced in these male reproductive organs.
3. Another term for in vitro fertilizations
4. These animals lay eggs.
5. A type of fission in amoeba
Junior Science Topic - Reproduction In Animals. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 8, CBSE syllabus, chapter 09)
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