NCERT Exemplar for Class 8 Science Solutions Chapter 9 Reproduction in Animals

Multiple Choice Questions

1. Sets of reproductive terms are given below. Choose the set that has an incorrect combination.

(a) sperm, testis, sperm duct, penis

(b) menstruation, egg, oviduct, uterus

(c) sperm, oviduct, egg, uterus

(d) ovulation, egg, oviduct, uterus

Ans: (c) sperm, oviduct, egg, uterus

The testis is responsible for the release of sperm. To ejaculate the sperm, the sperm duct opens up into the penis. During menstruation, the unfertilized egg is released via oviduct. In humans, sperm is discharged into the oviduct, where it fertilizes the egg, resulting in a zygote. The ovary produces eggs, which are then ovulated. Ovulation results in the release of the egg. The uterine tubes are also referred to as the oviduct.

Hence, option (c) is the right answer.

2. In humans, the development of fertilized eggs takes place in the

(a) ovary

(b) testis

(c) oviduct

(d) uterus

Ans:  (c) oviduct

In humans, the fallopian tube is where the fertilized egg develops first (oviduct). After fertilization, the zygote enters the uterus on the third day (morula stage).

Hence, option (c) is the proper response.

3. In the list of animals given below, a hen is the odd one out.

human being, cow, dog, hen

The reason for this is

(a) it undergoes internal fertilization.

(b) it is oviparous.

(c) it is viviparous.

(d) it undergoes external fertilization.

Ans: (b) it is oviparous.

Hens reproduce by laying eggs. It lays eggs with a calcium-rich shell. Internal fertilization allows sperm to fertilize the egg without passing through a thick calcium shell. Hence, option (b) is the proper response.

4. Animals exhibiting external fertilization produce a large number of gametes. Pick the appropriate reason from the following.

(a) The animals are small in size and want to produce more offspring.

(b) Food is available in plenty of water.

(c) To ensure a better chance of fertilization.

(d) Water promotes the production of a large number of gametes.

Ans: (c) To ensure better chance of fertilisation.

The process of fusion of male and female gametes outside the body or in the environment is known as external fertilization. Since there are only a few possibilities of fertilization when an animal releases gametes into the environment, a large number of male gametes are created to increase the chances of fertilization.

Hence, option (c) is the proper response.

5. Reproduction by budding takes place in

(a) hydra

(b) amoeba

(c) paramecium

(d) bacteria

Ans: (a) hydra

Budding is a form of asexual reproduction wherein the formation of a daughter from a tiny outgrowth on the parent body is termed bud. It can be found in sponges, coelenterates, yeast, and other organisms.

Hence, option (a) is the proper response.

6. Which of the following statements about reproduction in humans is correct?

(a) Fertilisation takes place externally.

(b) Fertilisation takes place in the testes.

(c) During fertilization egg moves towards the sperm.

(d) Fertilisation takes place in the human female.

Ans: (d) Fertilisation takes place in the human female.

The female reproductive system is intended to facilitate a variety of purposes. It produces ova, necessary for reproduction. The system is set up to convey the ova to the fertilization zone. Fertilisation occurs in the Fallopian tubes. The next step for fertilized eggs is to implant in the uterine walls and establish a pregnancy. Sperms can migrate past the cervix, into the uterus, and to the end of a fallopian tube after they enter the vaginal tract. Fertilization occurs when sperm can combine with an egg.

Hence, option (d) is the proper response.

7. In human beings, after fertilization, the structure which gets embedded in the wall of the uterus is

(a) ovum

(b) embryo

(c) foetus

(d) zygote

Ans: (d) zygote

The zygote is a single-celled entity that forms as a result of fertilization. A series of cell divisions occur in the zygote which results in the formation of a hollow cell mass known as the blastocyst.

Hence, option (d) is the proper response.

8. Aquatic animals in which fertilization occurs in water are said to be:

(a) viviparous without fertilization.

(b) oviparous with external fertilization.

(c) viviparous with internal fertilisation.

(d) oviparous with internal fertilization.

Ans: (b) oviparous with external fertilisation.

Fertilization occurs in water in aquatic animals. They release their gametes in water which further forms a zygote. They release their gametes in water which further forms a zygote. External fertilization is defined as fertilization that occurs outside of the body, whereas oviparous animals are those that develop their embryos in the egg.

Hence, option (b) is the proper response.

9. After fertilization, the resulting cell which gives rise to a new individual is the

(a) embryo

(b) ovum

(c) foetus

(d) zygote

Ans: (d) zygote

Male and female gametes combine to produce a zygote after fertilization. The zygote transforms to become a two-cell embryo. The embryo then divides into stages, resulting in the production of morula and blastula. The embryo gives birth to a new individual.

Hence, option (d) is the proper response.

10. In human beings, the correct sequence of events during reproduction is

(a) gamete formation, fertilisation, zygote, embryo

(b) embryo, zygote, fertilisation, gamete formation

(c) fertilisation, gamete formation, embryo, zygote

(d) gamete formation, fertilisation, embryo, zygote

Ans: (a) gamete formation, fertilisation, zygote, embryo

Male and female gametes fuse to produce a new progeny in the process of sexual reproduction. Human reproduction begins with the development of male and female gametes, which are then fertilized to produce an embryo.

Both male and female gametes go through a meiotic cell division during the production of gametes.

Fertilization happens when male and female gametes are transferred and fused, resulting in the development of a diploid zygote.

Hence, option (a) is the proper response.

Very Short Answer Questions

11. Although 2 cells called gametes fuse, the product formed is a single cell called a zygote. Justify.

Ans: The sperm and the ovum merge during the fertilization process. In order to produce the zygote, the contents of the sperm cell are transported into the egg. Hence, the product is a single-celled zygote.

12. Stages in the life cycle of silkworm are given below. Write them in sequential order.

pupa, silkworm, egg, silkmoth

Ans: The following is the right order of phases in the silkworm's life cycle:

Egg

↓

Pupa

↓

Silkworm

↓

Silkmoth

13. What is the importance of reproduction?

Ans: The immediate purpose of reproduction is to save the populations from extinction.

14. In markets, eggs of birds are available but never eggs of dogs. Why?

Ans: Dogs do not lay eggs, instead, they produce puppies. As a result, there are no dog eggs in the market.

15. The eggs of frogs do not have shells for protection, yet they are safe in the water. How?

Ans: The eggs are covered with a jelly-like substance by the female frog, which causes them to float to the water's surface and protects them from damage.

Short Answer Questions

16. Fill up the blanks with the terms given below:

body, asexual, binary, single, nucleus

Amoeba is a ___________ celled organism. It reproduces by ___________ reproduction. The process of reproduction begins by the division of its ___________ into two. This is followed by the division of its ___________ into two. This type of reproduction is called ___________ fission.

Ans:  Amoeba is a single-celled organism. It reproduces by asexual reproduction. The process of reproduction begins by the division of its nucleus into two. This is followed by the division of its body into two. This type of reproduction is called binary fission.

17. The term metamorphosis is not used while describing human development. Why?

Ans: Metamorphosis is a biological process in which an organism's form changes dramatically from one stage to the next in its life cycle, such as from the caterpillar to pupa and pupa to adult. Metamorphosis occurs in a variety of insects, fishes, amphibians, cnidarians, tunicates, and many more. Metamorphosis is not something that humans go through.

18. Mother gives birth to a baby but the baby has characters of both parents. How is this possible?

Ans: Due to sexual reproduction, the child possesses the characteristics of both the mother and father. The process of sexual reproduction involves the fertilization of male and female gametes, which results in the development of a zygote.

As a result of the two parents' genetic material being combined, a new creature is created, and the child possesses the characteristics of both parents.

19. How is reproduction in hydra different from that in amoeba?

Ans: Budding is an asexual reproduction method in which a new organism emerges from a bud or protrusion on the parent's body. Budding is the method by which Hydra reproduces. In binary fission, the parent cell divides into two daughter cells, such as in Amoeba.

20. State whether the following statements are True or False. If false, correct the statement:

(a) External fertilisation can occur both in water and on land.

Ans: False. External fertilization is only possible in the water.

(b) The eggs of fish are covered by hard shells for protection.

Ans: False. Fish eggs are protected by a jelly-like material.

(c) Human egg has a head, middle piece and tail.

Ans:  False. Human sperm consists of three parts: a head, a middle section, and a tail.

(d) In adult human females, a single mature egg is released into an oviduct every month.

Ans: True.

21. Why do only male gametes have a tail?

Ans: Male gametes (sperms) are motile. The tail helps the sperm swim through the female's reproductive tract and into the oviduct. The male reproductive system is where sperms are formed. Sperms are single-celled entities with a head, midsection, and tail. The acrosome, which is located at the tip of the sperm head, allows the sperm to reach the egg. The mitochondria, which provide the energy required for the tail to move, are located in the midpiece. To drive the sperm towards the egg, the tail swings back and forth in whip-like movements.

22. What does Fig. 9.1 represent?

Ans: This figure represents binary fission in the amoeba which involves the division of its nucleus into two followed by the division of its body into two.

23. Observe the figure given as Fig. 9.2 and answer the questions that follow.

(a) Label A and B.

Ans: A-Sperm     B- Ovum

(b) Identify the process.

Ans: Fertilisation is the process.

(c) What happens during this process and what is formed?

Ans: Fertilisation results in the formation of the zygote.

Long Answer Questions

24. How can we say that fish exhibits external fertilization?

Ans: In an aquatic environment, external fertilization keeps the eggs from drying out. Male and female fish both release eggs and sperm into the sea. Sperm swim around in the water at random and come into contact with the eggs. The sperm nucleus travels into the egg and unites with it. External fertilization happens when fertilization takes place outside the female body, in water. Given that a vast majority of fish (>95 percent) experience external fertilization, it's only natural that the eggs develop outside the mother's body.

25.

After observing Fig. 9.3 answer the following.

a. Read the following statements and label them in the figure:

(i) The part which produces female gametes.

Ans: Ovary

(ii) The part where the development of the baby takes place.

Ans: Uterus

(iii) The part through which the developing embryo passes to reach the uterus.

Ans: Oviduct

b. Explain the future development of the embryo that would take place after it gets embedded in the uterus.

Ans: The zygote is formed once the egg and sperm have fused.

The blastula, which is lodged in the uterus, is formed by several divisions of the zygote. The embryo now proceeds through the gastrulation process, which results in the formation of three germ layers: endoderm, mesoderm, and ectoderm. The placenta develops next. Mesoderm is also linked to trophoblast tissue from the umbilical cord, which transfers nutrients and wastes from the fetal circulation to the placenta. The embryo then grows and takes on a human look in the last stage. 

26. Hens and frogs are both oviparous exhibiting different types of fertilisations. Explain.

Ans: Internal fertilization occurs in hens. Inside the body, the fertilized egg grows into an embryo. The embryonic development of a chick, on the other hand, occurs outside the body.

Frogs are oviparous, which means that both zygote fertilization and embryo development take place outside the body.

27. Observe the following figures.

(a)

(b) 

(c)

(d)

(i)Identify the stages (a) to (d) in Fig. 9.4 during the development of the human baby.

Ans: a) Embryo embedding in the uterus

b) Fertilisation

c) Zygote formation and embryo development

d) Zygote showing fusion of nuclei.

(ii) Arrange the stages in the correct sequence of development.

Ans: The correct sequence is as under:

(c), (b), (d), (a)

(iii) Explain the development that takes place in any one stage

Ans: Zygote formation

Introduction: Reproduction in Animals

The process by which one creature generates offspring is known as reproduction. It is one of the most fundamental processes in all known living forms. Every living creature we observe is a direct outcome of reproduction.

In animals and plants, there are two ways to reproduce:

• Sexually

• Asexually

There are several techniques of reproduction depending on the number of parents involved. Every living entity reproduces in one of two ways: through sexual reproduction or through asexual reproduction.

Sexual Reproduction

It's a type of reproduction in which gamete cells from two different organisms, one male and one female, unite to produce a single zygote. Half of this zygote's genetic information is shared with the father, while the other half is shared with the mother. There are many distinct mechanisms of sexual reproduction in both plants and animals, yet the principles remain the same. Both genetically and physiologically, the newly developed individual generated through sexual reproduction differs from its parents.

Asexual Reproduction

It is a type of reproduction in which just one organism participates. The offspring is genetically identical to the mother and nearly invariably has the same number of chromosomes as the mother. As a result, they are referred to as clones. They're also identical replicas of their parent cell.

Fission

It's an asexual reproduction method in which a single cell splits into two.

• The nucleus is divided first, then other cell organelles in the cytoplasm, and lastly the cytoplasm itself.

• As a result, one parent cell produces two offspring.

• Amoeba is a good example. Amoeba reproduces by dividing into two cells, a process known as binary fission.

• Multiple fission occurs when one parent cell produces a large number of daughter cells.

Budding 

Budding is an asexual way of organism reproduction. The process of creating a new creature from a piece of the parent's body is explained in this video. It becomes detached whenever both genetically and physiologically, a bud is created. It becomes detached and develops into a new organism. As it matures, the newly evolved creature remains connected. The mature organism leaves scar tissues behind when it separates from the parent organism. The newly created creature is a genetic clone of the parent due to the fact that the reproduction is asexual. In Hydra, regenerative cells cause a bud to extend as an outgrowth after the repeated division of cells at the same location. These buds then evolved into new little individuals, which separate from the parent body once fully-fledged.

Cell Division

Cell division is at the heart of reproduction. Life cannot survive without cell division. Two separate types of cell divisions are involved in the two sorts of reproductive processes.

Mitosis

Mitosis occurs when a single cell divides into two identical daughter cells. A single division follows a single replication of DNA. In this form of division, the number of chromosomes is maintained. Asexual reproduction involves this form of division. It's also employed for tissue development, repair, and regeneration.

Meiosis

A single cell divides twice during meiosis to generate four haploid daughter cells. These cells are the gametes in males and females - the sperm and eggs. Two stages of the meiosis process occur. Each stage is further divided into stages.

Male Reproductive System

The testes, scrotum, spermatic ducts, male accessory glands, and penis are part of the male reproductive system. These organs collaborate to create sperm, the male gamete, male sex hormones, and other semen components. Both the reproductive and urinary systems include the penis and urethra. The remaining male reproductive system consists of the scrotum, seminal vesicles, vas deferens, testicles (testes), and prostate. The Penis has a cone-shaped root related to the structures of both the pelvic bones and the lower abdominal (visible section of the shaft) glands. The urethra's opening, located near the tip of the penis, is a conduit that transports sperm and urine. Corona refers to the base of the penis.

Female Reproductive System

The female reproductive system is designed to serve a variety of purposes. It produces ova, which are egg cells that are necessary for reproduction. The mechanism is set up to convey the eggs to the fertilization area. Along with the sperm, egg fertilization takes place in the Fallopian tubes. The next step for fertilized eggs is to implant them in the uterine walls and start the process of pregnancy. The female reproductive system is responsible for creating female sex hormones and the tasks listed above, which are necessary for the reproductive cycle to continue.

There are two ovaries in the female reproductive system and oviducts, uterus, vagina, cervix, and external genitalia.

These components, coupled with a pair of mammary glands that are functionally and physically connected, help in ovulation, fertilization, birth, and child care.

Estrogen

The principal female sex hormone released by the ovaries is estrogen, also known as estrogen. It is in charge of developing female reproductive organs, secondary sexual traits, the formation of the female gamete, the ovum, and the menstrual cycle maintenance.

Ovum

The female gametes known as ovum or ova are produced by the ovary (plural). Every month, the right side ovary releases a single developed egg or ovum into humans’ oviduct/fallopian tube. The ovum is a single cell that is much bigger than sperm. The oviduct transports it to the uterus since it is non-motile.

Fertilization

Fertilization is the process of the male and female gametes fusing. Both haploid (single) chromosome-containing gametes merge, resulting in a diploid (double) number of chromosomes. A zygote is a name given to the fertilized ovum. Human fertilization occurs in the fallopian tube, and the zygote is subsequently transported to the uterus. It divides several times inside the uterus, expands, and develops into an embryo.