Class 8, SCIENCE - Chapter 9 Reproduction in Animals Notes, NCERT Solutions & Frequently Asked Questions

SCIENCE 

Class 8 - Chapter 9

Reproduction in Animals

Notes, NCERT Solutions & Frequently Asked Questions 

-- Notes --

⭐Introduction to Reproduction:- 

👉Reproduction is the process of giving rise to an offspring.

👉Reproduction is essential for the continuation of a species.

👉There are two types of reproduction:-

a) Asexual reproduction:- The type of reproduction in which only a single parent is involved is called asexual reproduction.

• There is no mixing of genetic information.

• Eg: budding in Hydra

b) Sexual reproduction:- The type of reproduction, which involves two parents to give rise to an offspring is called sexual reproduction.

• The males and females have different reproductive parts or organs.

• These organs produce the male and female gametes, which fuse together to form the offspring.

• Genetic information from both parents is inherited.

• Eg: humans

⭐ Fission:- It is a type of asexual reproduction in which a single-celled organism divides into two.

• Division of nucleus is followed by division of other cell organelles in the cytoplasm and finally the cytoplasm. 

• Thus, two cells are produced from one parent cell.

• Fission is of two types:-

a) Binary Fission:- When a single cell (parent cell) divides into only two cells. 

• Eg:- Amoeba 

b) Multiple Fission:- If one parent cell gives rise to many daughter cells, this type of fission is called multiple fission.

• Eg:- Yeast

⭐ Budding:- A bud starts as an outgrowth on the parent body.

• As this bud grows, it becomes a new individual organism.

• In some organisms, the buds remain attached to the parent’s body (Eg:- Yeast).

• In some organisms, it detaches from the parent body and develops into a complete mature individual (Eg:- Hydra).

• This type of reproduction is called budding.

⭐ Cell Division:-  Cell division is the process in which a parent cell divides into two or more daughter cells. 

• Reproduction essentially involves cell division.

• Without cell division life will not propagate.

• Cell division provides more cells:-

      - For growth

      - Regeneration

      - Repair and damage control

      - Gamete formation

• The both types (Sexual & Asexual) reproductive processes involve two different types of cell divisions.

• The two types of cell divisions are:-

a) Mitosis:- Mitosis is a process where a single cell divides into two identical daughter cells.

• DNA replication occurs once followed by a single division.

• The number of chromosomes is maintained in this type of division.

• This type of division happens in asexual reproduction.

• It is also used for growth, repair and regeneration of tissues.

b) Meiosis:- This is a type of cell division in which a single cell divides into four haploid cells.

• DNA replication occurs once followed by two divisions.

• The numbers of chromosomes are halved in meiosis.

• Meiosis takes place in sex organs to produce haploid gametes.

• Thus, the gametes have only half the number of chromosomes in them.

⭐Sexual Reproduction in Humans:- Reproduction in human beings is by sexual reproduction where both the male and female gametes fertilize to give rise to an embryo.

👉Male Reproductive System:-

• The male reproductive system consists of a pair of testes, a pair of sperm ducts and a penis.

• The testes are located outside the male body in a pouch called scrotum.

• Testosterone:- Testosterone is the primary male sex hormone and is produced by the testes.

 -- Testosterone is responsible for the development of sex organs, production of sperms and also the development of secondary sexual characteristics.

• Sperms:- Sperms are the male gametes produced by testes in humans.

 -- Millions of sperms are produced by the testes in a day.

 -- Each sperm is a single, microscopic cell having a head, a middle piece and a tail as its parts.

 -- Head contains a nucleus with a single set of chromosomes.

 -- The middle piece contains a large number of mitochondria that provide energy during active movement.

 -- Sperm is a motile gamete, which moves through the female reproductive tract with the help of the tail.

👉Female Reproductive System:-

• The female reproductive system consists of a pair of ovaries, a pair of fallopian tubes (oviducts) and a single uterus.

• Ova are produced by ovaries.

• Fallopian tubes (oviducts) carry the ova from ovaries to the uterus.

• Uterus holds the growing embryo/foetus and thus helps in holding the pregnancy.

• Oestrogen/Estrogen:- Estrogen or Oestrogen is the primary female sex hormone secreted by ovaries.

 -- It is responsible for the development of female reproductive organs, secondary sexual characteristics, development of female gamete (i.e. production of Ovum and maintenance of menstrual cycle.)

• Ovum:- The ovary produces the female gametes known as ovum(singular) or ova (plural).

 -- In human beings, a single mature egg or ovum is released into the oviduct/fallopian tube by the respective side ovary every month.

 -- The ovum is a single cell and is much larger than the sperm.

 -- It is non-motile and is carried to the uterus by the oviduct.

👉 Watch the video by clicking the link given below to know more about human reproduction :- 

Animation of Human Reproduction

👉Fertilization:- Fertilization is the process of fusion of the male gamete with the female gamete.

• Both the gametes containing haploid (single) set of chromosomes fuse and thus maintain the diploid (double) number of chromosomes.

• The fertilized ovum is now called a zygote.

• In human fertilization takes place in the fallopian tube and then the zygote is carried to the uterus.

• Inside the uterus, it undergoes repeated divisions and grows and becomes an embryo.

• Fertilisation is mainly of two types :- 

a) Internal Fertilisation:- Fertilisation that takes place inside the female body is called internal fertilisation. 

Eg:- Humans, Dogs, Cows etc.

b) External Fertilisation:- Fertilisation that takes place outside the female body is called external fertilisation. 

Eg:- frogs, fish, starfish etc.

👉 Foetus:- It is the stage of embryo in which all the body parts are identifiable in its developmental stage.

👉 Zygote:- The nuclei of sperm(n) and egg(n) are fused during fertilization, to form a single nucleus. Egg after fertilization is called Zygote.

👉 Embryo:- Zygote, during its development, divides repeatedly to form a ball of cells. The cells then form groups to form tissues and ultimately organs of the body. This structure is called embryo.

👉 Parturition:- The process of giving birth to a child/young ones after the gestation period. In humans, gestation period is about 9 months. 

Watch the video of parturition by clicking the link given below :-

Parturition

👉 Viviparous:- Animals such as human beings, cows and dogs which give birth to the young ones are called Viviparous animals.

👉 Oviparous:- Animals such as hen, frog and butterfly which lay eggs are called oviparous animals.

👉 Tadpoles:- In the life process of a frog, we find three distinct stages, that is egg → tadpole → adult. These tadpoles get transformed into adults which are capable of jumping and swimming, and are finally transformed into frog.

👉 Metamorphosis:- The drastic change which transforms a larva into an adult in case of frog is called metamorphosis.

👉 Cloning:- Cloning is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two organisms.

-- NCERT Solutions --

Question 1.- Explain the importance of reproduction in organisms.

Answer:- Importance of reproduction:-

 • Reproduction is essential for the continuance of the human species.

 • It is the process of producing new individuals from the living organisms.

 • Reproduction ensures the passage of traits and habitats from generation to generation.  

 • Without reproduction the species will be vanished from the earth and there is no world without species.

Question 2.- Describe the process of fertilization in human beings.

Answer:- Human reproduction is brought about by formation and fusion of the male and female gametes. The male gametes (sperms) are produced by the testis and the female gametes  (ovum) is produced by the ovary. 

During copulation/intercourse, the male releases sperm into the female reproductive tract/vagina. Since the sperm is a motile gamete, it will swim in the female reproductive tract to reach the ovum in the fallopian tube.

The process of fertilization happens when the male and female gametes fuses together in the fallopian tube. The end product of fertilization is called a zygote, which will develop further and become a foetus in the womb.

Question 3.- Choose the most appropriate answer.

a) Internal fertilisation occurs:- 

      i) In the female body. 

      ii) Outside female body. 

      iii) In male body.

      iv) Outside male body

Answer:- i) In a female body 

b) A tadpole develops into an adult frog by the process of

       i) Fertilisation. 

       ii) Metamorphosis 

       iii) Embedding 

       iv) Budding 

Answer:-  ii) Metamorphosis

c) The number of nuclei present in a zygote is 

        i) None 

        ii) One 

        iii) Two

        iv) Four 

Answer:- ii) One

Question 4.- Indicate whether the following statements are true (T) or false (F).

a) Oviparous animals give birth to young one.   

Answer:- F  (Oviparous animals lay eggs and the young ones develop inside it.)

b) Each sperm is a single cell.

Answer:- T  

c) External fertilisation takes place in frogs.

Answer:- T 

d) A new human individual develops from a cell called gamete.

Answer:- T

e) Egg laid after fertilisation is made up of a single cell.

Answer:- T

f) Amoeba reproduces by budding.

Answer:- F   (Amoeba reproduces asexually through binary fission.) 

g) Fertilisation is necessary even in asexual reproduction.

Answer:- T

h) Binary fission is a method of asexual reproduction.

Answer:- T

i) A zygote is formed as a result of fertilisation.

Answer:- T 

j) An embryo is made up of a single cell.

Answer:- F   (Embryo is a multicellular structure.)

Question 4.- Give two differences between a zygote and Foetus.

Answer:- Difference between zygote and foetus:-

Question 5.- Define asexual reproduction. Describe two methods of asexual reproduction in animals.

Answer:- Asexual Reproduction:- It is a mode of reproduction that does not entails the union of sex cells or gametes. There are different types of asexual reproduction (binary fission, budding vegetative propagation, spore formation, fragmentation). There is no gamete formation in this type of reproduction. Animals like Hydra, Amoeba undergo asexual mode of reproduction. 

• Two types of Asexual reproduction are:-  

 -- Budding:- It is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. These buds develop into tiny individuals and when fully they mature and detach from the parets body and become a new independent individual. Eg:- Hydra. 

 -- Binary Fission:- In this type of asexual reproduction the body of the organism mainly unicellular organism divides into two. Each of the two daughter cells are alike. Eg:- Amoeba.

Question 6.- In which female reproductive organ does the embryo get embedded?

Answer:- The embryo gets embedded in the wall of the uterus for further development.

Question 7.- What is metamorphosis? Give examples.

Answer:- Metamorphosis:- It means sudden change which happens while developing. The animals that undergoes metamorphosis are -  

  • Butterfly (egg→larva→pupa→adult) 

  • Frog (egg → tadpole → adult)

Question 8.- Difference between internal fertilisation and external fertilisation.

Answer:- Difference between internal fertilization and external fertilization:-

Question 9.- Complete the crossword puzzle using the hints given below.

Across 

1. The process of the fusion of the zygotes. 

6. The type of fertilisation in hen. 

7. 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 the fertilized egg. 

4. These animals lay eggs. 

5. A type of fission in amoeba.

Answer:-

Across 

1. The process of the fusion of the zygotes - FERTILIZATION

6. The type of fertilisation in hen - INTERNAL

7. Term used for bulges observed on the sides of the body of hydra - BUDS

8. Eggs are produced here - OVARY

Down 

2. Sperms are produced in these male reproductive organs - TESTES

3. Another term for the fertilized egg - ZYGOTE

4. These animals lay eggs - OVIPAROUS

5. A type of fission in amoeba – BINARY

-- Frequently Asked Questions -- 

Question 1.- What is ‘Budding’?

Answer:- A form of asexual reproduction in which a new individual develops from some generative anatomical point of the parent organism.

Question 2.- What is a ‘Hydra’?

Answer:- Genus of invertebrate freshwater animals of the class Hydrozoa (phylum Cnidaria) is called a ‘Hydra’.

Question 3.- What is an ‘Embryo’?

Answer:- An unborn human or animal in the earliest stages of growth when its basic structures are being formed is called as an ‘Embryo’.

Question 4.- Explain the difference between a Zygote and a Foetus?

Answer:- 

 • Zygote -- Zygote is the first stage of development. It is developed by the fusion of male and female gametes. It is a single cell. The zygote is divided to form an embryo. It lasts for a few weeks and then develops into the next stage.

 • Foetus -- Foetus is the last stage of the development of an organism. Foetus usually undergoes an internal development. The stage of an embryo that shows all the main body parts of a mature organism.

- By Durgesh Pandey 

Eklavya Coaching Institute

H-2/25, Gali No.-23, Kunwar Singh Nagar, Nangloi, New Delhi -110041