Q 7 – In the list of animals given below, hen is the odd one out. ‘human being, cow, dog, hen’ The reason for this is (a) it undergoes internal fertilisation (b) it is oviparous (c) it is viviparous (d) it undergoes external fertilization
Q 8 – Animals exhibiting external fertilisation 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 offsprings. (b) Food is available in plenty in water. (c) To ensure better chance of fertilisation. (d) Water promotes production of large number of gametes.
Q 13 – The fusion of male and female gametes that takes place outside the body of the female is called (a) internal fertilisation (b) fertilisation (c) external fertilisation (d) reproduction
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 high chance of survival. It occurs mostly in mam¬mals; e.g., in human being, cow, buffalo, etc.
Q 23 – Explain briefly the external fertilisation.
Ans. In external fertilisation, fusion of male and female gametes take place outside the female body. The female discharge many eggs in the water and the male discharge sperms. The sperms swim to the eggs and fertilise them. It occurs in most of the aquatic animals like frog, fish, starfish, etc.
Q 24 – Mother gives birth to a baby but the baby has characters of both parents. How?
Ans. Human beings show sexual reproduction. During fertilisation, two gametes, one from the mother and the other from father, fuse together to form zygote. Therefore baby developed from zygote has characters of both parents though mother gives birth to a baby.
Ans. The male gamete is called sperm. It is produced by 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 the small nucleus
Ovum are the female gamete. They are also called egg. They are produced by the female reproductive organ. They consist of larger nucleus. Both sperm and ovum are reproductive cells and contain single cell.
Q 26 – Though hen and frog both are oviparous but they have different types of fertilisation. Justify.
Ans. In hen, internal fertilisation takes place. The fertilised egg develops into an embryo inside the body. But development of chick from the embryo takes place outside the body. On the other hand, frog shows external fertilisation. The female frog discharge many eggs in the water and the male frog discharge sperms. The sperms swim to the eggs and fertilise them.
Q 27 – 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.
Q 28 – 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.
Q 29 – Describe the male reproductive organs with the help of a labelled diagram.
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.
Q 30 – Describe female reproductive organs with the help of a labelled diagram.
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.’
Q 31 – Explain with a diagram the development of an embryo.
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. 9.7(a)].
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 foetu (Fig. 9.16).
Q 32 – 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.
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.’
Q 33 – 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.
Q 34 –Ram with his family went to a picnic spot near a pond. He saw some jelly-like mass floating on the sides of the pond. He asked about this to his father. His father explained him that these are frog’s egg and are millions in number. Ram wondered if all of them get hatched, Q 34 – what will happen to other aquatic animals?
What type of fertilisation is shown by frog?
Why do frog lay eggs in large amount?
Is Ram’s concern about hatching of too many eggs at a time will affect the aquatic animals correct? Why?
Mortality rate is very high for tadpoles as their predators are more. Many of the eggs do not develop due to being not get fertilised. So for continuation of their species, they lay egg in large amount.
No, his concern is not correct because most of the eggs either never develops or are preyed by other animals. So survival chance of a frog from its egg to an adult frog is very low.
Ram is inquisitive, future thinker and eco-concerned.
