Class 4 Science Chapter 6 Question Answers - Reproduction in Animals

Q1: What are sperm and ovum? Explain.
Ans: The male gamete is called sperm. It is produced by the male reproductive organ, testes. Structurally, it consists of a head attached to a long tail. The tail helps the sperm to move around. The head bears a small nucleus.
Ovum is the female gamete. They are also called eggs. They are produced by the female reproductive organ. They consist of a larger nucleus. Both sperm and ovum are reproductive cells and contain a single cell.

Q2: Explain the process of fertilisation in brief.
Ans: Fusion of the male and female gamete, i.e., sperm and egg, is called fertilisation. During fertilisation, the nuclei of the sperm and the egg fuse to form a single nucleus, resulting in the formation of a fertilised egg or zygote.

Q3: What is internal fertilisation? Explain briefly.
Ans: Fertilisation which takes place inside the female body is called internal fertilisation. In this, a smaller number of ova or eggs are produced. Offsprings have a high chance of survival. It occurs mostly in mammals; e.g., in human beings, cows, buffalos, etc.

Q4: What is the life cycle of a frog? Explain briefly.
Ans: There are mainly three distinct stages in the life cycle of a frog:
egg → tadpole (larva) → adult.
Tadpoles look different from the adults. After some time, tadpoles are converted into an adult frog.

Q5: Explain two modes of reproduction with examples.
Ans: There are two modes of reproduction:

• Sexual reproduction: This type of reproduction takes place by the fusion of male and female gametes; e.g., Human beings, mammals like cows, buffalos, etc.
• Asexual reproduction: This mode of reproduction involves only a single parent; e.g., Hydra, Amoeba, yeast, etc.

Q6: What does magnesium burn to form?
Ans: Magnesium burns to form magnesium oxide and produces heat and light.

Q7: Explain what is foetus.
Ans: The embryo continues to develop in the uterus. It gradually develops different body parts such as hands, legs, head, eyes, etc. The stage of the embryo in which all the body parts can be identified is called a foetus. After its development is complete, the mother gives birth to the baby.

Q8: What is deforestation?
Ans: The cutting of trees on a large scale is called deforestation.

Q9: What are viviparous and oviparous animals?
Ans: The animals which give birth to young ones are called viviparous animals and those which lay eggs are called oviparous animals. For example, Mammals including human beings are viviparous animals and hens, lizards, all birds, etc., are oviparous animals.

Q10: Explain in short the life cycle of silkworm.
Ans: The life cycle of a silkworm is completed in four stages: egg → larva or caterpillar → pupa → adult. In the silkworm, the caterpillar or pupa looks very different from the adult moth.

Q11: How are babies produced through IVF technique? What are such babies called?
Ans: IVF (In Vitro Fertilisation), is an artificial type of fertilisation. Some women’s oviducts are blocked and so they cannot bear babies because sperms cannot reach the egg for fertilisation. In such cases, freshly released eggs and sperms are kept together for a few hours for IVF (fertilisation outside the body). In case fertilisation occurs, zygote thus formed is allowed to develop for a week and then it is placed in the mother’s uterus. Complete development of baby occurs in uterus and is born like any other baby. Babies born through this technique are called test tube babies.

Q12: Explain in brief the process of binary fission.
Ans: Amoeba reproduces through the process of binary fission. Binary fission is another method of asexual reproduction. Amoeba is a single-celled organism. It begins the process of reproduction by the division of its nucleus into two nuclei followed by division of its body into two, each part receiving a nucleus. Finally two daughter cells are produced from one parent Amoeba. This type of asexual reproduction in which an animal reproduces by dividing into two individuals is known as binary fission.

Q13: What is cloning? Explain how first cloned mammal was born.
Ans: Cloning is the production of an exact or a true copy of a cell, any other living part, or a complete organ¬ism by asexual reproduction. Cloning of an animal was successfully performed for the first time by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland. They cloned the sheep named Dolly on July 5, 1996.
Cloning

In the process of cloning Dolly, a cell was collected from the mammary gland of a female Finn Dorsett sheep [Fig. 9.17(a)]. Meanwhile, an egg was obtained from a Scottish blackface ewe [Fig. 9.17(b)]. The nucleus was removed from the egg. Then, the nucleus of the mammary gland cell from the Finn Dorsett sheep was inserted into the egg of the Scottish blackface ewe whose nucleus had been removed. This egg was implanted into the Scottish blackface ewe. The egg developed normally and finally Dolly was born. Cloning of Dolly was a successful attempt. However, many clones often die soon after birth. Sometimes cloning also leads to certain abnormalities among clones. Unfortunately, Dolly died on 14th February, 2003 due to a certain lung disease.

Q14: Describe female reproductive organs with the help of a labelled diagram.
Ans:
The female reproductive organs

The female reproductive organs mainly consist of a pair of ovaries, oviducts or fallopian tubes, uterus and vagina. The female gametes called ova or eggs are produced by ovary. In human beings, a single matured egg is released into the oviduct by one of the ovaries every month. Uterus is the part inside which the embryo grows and develops finally into a baby. An egg or ovum is a single cell. Vagina is the part which receives the penis during copulation. The following diagram shows these organs clearly.

Q15: What do you mean by metamorphosis? How does metamorphosis take place in frog? Explain with a diagram.
Ans: The transformation of the larva into an adult through drastic (sudden or abrupt) changes is called metamorphosis. For example, a moth emerging out of the cocoon, an adult frog from a tadpole, etc., undergo metamorphosis.
Frog undergoes through three stages during its life cycle in which eggs laid down by frogs transform into tadpoles (larva) and finally into an adult following the process of metamorphosis. The following diagram clearly shows this process.
Frog Life Cycle
Q16: What do you mean by reproduction? Describe various modes of reproduction.
Ans: Reproduction is an important process which is responsible for the continuity of life on the planet earth. In this process, an individual produces young ones of the same species. It helps in increasing the population of the same species on the earth, generation after generation. This is the fundamental feature which ensures the existence of all life forms on the earth. There are two modes of reproduction:

• Sexual reproduction: In this type of reproduction, both male and female parents are involved and they produce different gametes called male gametes or sperms and female gametes or ova (egg) respectively. Both fuse to form zygote which finally develops into foetus. For example, mammals including human beings higher invertebrates and all vertebrates undergo sexual reproduction.
• Asexual reproduction: In this type of reproduction, only single parent is involved and gametes or sex cells are not produced. Budding, binary fission, etc., are different methods of asexual reproduc¬tion. Lower organisms like Hydra, Amoeba, yeast, etc., undergo asexual reproduction.

Q17: Describe the male reproductive organs with the help of a labelled diagram.
Ans:
Male Reproductive Organs

The male reproductive organs mainly consist of a pair of testes, two sperm ducts (vas deferens) and a penis. Male gametes called sperms are produced by the testes. Though the sperms are very small in size, each has a head, a middle piece and a tail. It is unicelled with all the usual cell components. Figure 9.14 shows the male reproductive organs in humans.

Q18: Explain with a diagram the development of an embryo.
Ans:
Foetus in the Uterus of female

An embryo is developed in the process of fertilisation. Fertilisation results in the formation of zygote which begins to develop into an embryo [Refer Fig. above].
The zygote divides repeatedly to give rise to a ball of cell (Refer Fig. 9.7(b)) which further begin to form groups that develop into different tissues and organs of the body. This developing structure is called an embryo. The embryo gets embedded in the wall of the uterus for further development [Refer Fig. 9.7(c)]. The embryo continues to develop in the uterus. It gradually develops different body parts. This developing stage of embryo is called foetus.

Q19: What is budding? Explain.
Ans: Budding is type of asexual reproduction in which an organism or new individual develops from an outgrowth from a single parent. This outgrowth is called bud. On maturation this bud get separated from the parent’s body to grow into new individual. This process of reproduction is known as budding. For example, Hydra, yeast and sponges produce their young ones through the process of budding. In some organisms, like sponges, buds are not separated from their parent’s body and form a colony. They remain attached to parent’s body.

Q20: What is metamorphosis? Explain.
Ans: Some insects and animals undergo a series of changes after birth. Their young ones look quite different from them. The features of these young ones are completely different from the adults. A biological process in which larva transforms into an adult through drastic changes (sudden and abrupt changes) in the body of the animal during the life cycle of an invertebrate or amphibian is called metamorphosis. For example, frog, butterfly, etc., undergo metamorphosis.