Reproduction In Animals

In option (c), sperm is a male gamete, a part of male reproductive system, whereas the other three terms are related to the female reproductive system. As there is a mismatch, this option is an incorrect combination.

In option (a), all four terms are related to male reproductive system, and in option (b) and (d), all four terms are related to female reproductive system. As there is no mismatch, these options are correct combinations.

In humans, after fertilization, the fertilized egg travels to the uterus, where it gets fixed or attached to the walls of uterus, and further development takes place. The necessary blood and nutrient supply are maintained here.

The ovary is a female reproductive organ which releases the ovum, or unfertilized egg for fertilization.

Oviducts or fallopian tubes are situations where fertilization between a sperm and an ovum takes place.

Testis are male reproductive organs which produce sperm, or male gametes.

In the given list of animals, hen is the odd one because it is the only one which lays eggs, that is it shows oviparity. Humans, cow and dog are viviparous, i.e. they give birth to young ones.

All four organisms show internal fertilization, none of them fertilizes externally, thus these cannot be reasons for the hen being the odd one.

Although the animals exhibiting external fertilization produce a large number of gametes, the chances of fertilization of these gametes are quite low. This is because they are subjected to movements of water, air, rain and also can be destroyed or eaten up by other animals. Therefore a large number of gametes are produced to ensure fertilization of at least some of them.

The size of animals or availability of food is not related to the production of gametes. Water does not promote the production of a large number of gametes. Thus, these statements are not the correct option.

Reproduction in all the given organisms takes place through asexual methods. Hydra reproduces by the formation of buds on its body surface, which later develops into a new organism.

Amoeba, paramecium and bacteria multiply by dividing themselves into two parts, i.e. by binary fission method.

Fertilization or fusion of the male and female gametes takes place in the fallopian tubes, which are a part of the female reproductive system. Thus, in humans, fertilization takes place in the human female.

As the fertilization is taking place inside the female body, it is not external fertilization.

Testis is a part of the male reproductive system which has a role in the production of sperms, not fertilization.

During fertilization, the sperm moves towards the egg, because it has a tail and several mitochondria to facilitate this action.

In humans, the immediate product of fertilization is the zygote formed by the fusion of sperm and egg. This zygote undergoes repeated cell divisions white traveling its path from the fallopian tube to uterus, and this group of divided cells is called embryo, which gets embedded in the uterine walls.

Ovum is the infertility egg, and the fetus is the stage of intrauterine life when all body parts can be recognized, and look similar to a mature human being.

The aquatic animals in which fertilization takes place in water, lay unfertilized eggs and fertilization takes place when male gametes, already present in water, float up to them and fuse. Thus these animals are oviparous as they lay eggs, and exhibit external fertilization as the fusion of male and female gametes takes place outside the body of an organism .

As the other options do not show this combination, (b) is the correct option.

The immediate product of fertilization, formed by the fusion of male and female gametes, is called a zygote.

Ovum is the unfertilized egg. Zygote, on division develops into an embryo, which gets implanted in the maternal uterus. Foetus is the stage when all body parts of the baby are recognizable and appear similar to the adult beings.

In human beings, the process of reproduction starts by the formation of male and female gametes respectively in the male and female reproductive systems. This is followed by the fusion of these gametes inside the female body, a process called fertilization. The fertilized product of this process is termed as a zygote. As zygote divides and travels up to the uterus, it becomes the embryo which gets implanted in the uterine walls. Thus, the correct sequence is gamete formation, fertilization, zygote, embryo.

In the process of fusion of gametes during fertilization, there is mainly the fusion of nuclei of the male and the female gametes, i.e. the sperm and the ovum respectively. When a sperm reaches near the ovum, it comes in contact with it and releases its nucleus into the egg cell. There is fusion, thus of the nuclei of sperm and egg cell, inside the egg cell. The rest of the sperm body degenerates. And hence, the product formed is a single cell called zygote.

The correct sequence of stages of lifecycle of a silkworm is:

Egg, silkworm, pupa, silkmoth.

During its life cycle, the silkworm exhibits metamorphosis. This is the process where the young ones of an organism differ drastically from their adult forms in physical appearance. The silkworm starts its life as an egg, which changes into a crawling worm called the silkworm. It then weaves a covering around itself and gets shelled inside it, entering the next stage of life, called pupa. When, at maturity, the pupa breaks, an adult, winged, flying moth called the silkmoth comes out. This the final stage of silkworm's lifecycle.

Reproduction is the process of producing offsprings similar to one own self, of the same species. It is important for maintaining the continuation of species, generation after generation. Also, as the life cycles of different species are interlinked, the reproduction of one species affects the life of other species as well. Thus, it is an important process.

Dogs do not lay eggs. They are viviparous animals, which means they give birth to young ones directly, not by the means of the egg. Also, the fertilization in dogs is internal, which means that the fusion of gametes takes place inside the body of the organism itself. Thus, eggs of dogs are not available in the market.

Frogs show external fertilization, i.e. they lay unfertilized eggs in water, which get fertilized outside the body of the organism when a sperm reaches them. These eggs are protected by means of a jelly-like substance that binds these eggs together, and also provides slimy nature to help in floating of eggs.

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.

The term metamorphosis is used to describe a process of development of an organism, where the young ones differ drastically in physical appearance from their adult forms. The body parts of an adult are absent in the young ones. Instead, some other and different body parts may be present.

In humans, the body structure of a young one is similar to that of an adult human. All body parts and organs of an adult are present in a child also. Thus, it is not called metamorphosis.

In the first step of reproduction, there is a fusion of the male and the female gametic nuclei. In this, the nucleus of the male gamete, sperm, fuses with the nucleus of the female gamete, the egg cell. As the nuclei carry genes, which result in the expression of characters, the zygote resulting from such fertilization, possess both male and female characters.

Reproduction in hydra and amoeba is asexual, but the methods of reproduction are different. Hydra reproduces by the formation of buds on its body surface, which later develops into adult individuals. These buds appear as bulges from which the organism grows. This method of reproduction ensures the existence of parent hydra after reproduction.

In amoeba, reproduction takes place by binary fission. In this, there is a division of the nucleus of an amoeba into two equal halves, followed by division of the body of an amoeba into two halves. In this, the parent amoeba loses its existence in the process of forming new ones.

Hence, the mechanisms of reproduction in amoeba and hydra are different.

(a) False.

External fertilization occurs only in water and not on land because of lack of protective environment to the gametes, and lack of means of transfer of gametes on land. In water, the gametes are well protected and easily transferable.

(b) False.

The fishes exhibit external fertilization. The eggs layer are unfertilized and covered only by a slimy, jelly-like substance for protection. No hard shell is present.

(c) False.

Human egg is a single round cell, without any distinctive parts. Head, middle piece and tail are present in human sperm, which is the male gamete.

(d) True.

In humans, the ovaries alternatively release one mature egg cell every month into the oviducts or fallopian tubes.

The human male gamete, the sperm has to flow through the female reproductive tract to reach the fallopian tube, where it can fuse with the ovum. Thus, it requires an organ for rapid and efficient motility for transportation. The tail provides this function. The female gamete or the ovum has to travel very little distance, in which it is helped by the ovary and fallopian tube. Thus, it doesn’t require any tail.

Thus, only the male gamete has a tail.

The figure represents binary fission method of asexual reproduction, in which the division of a nucleus into two halves is shown. The given figure is of an amoeba undergoing the first stage of binary fission.

(a) A- human male gamete, sperm

B- human female gamete – egg cell/ovum

(b) The process has shown is of fertilization, where the male gametes or sperms have reached the female gamete or ovum, and one of the sperms is ready for fertilization.

(c) During the process of fertilization, there is a fusion of the nucleus of the male gamete (sperm) with the nucleus of a female gamete (ovum), inside the female body. This results in the formation of a zygote, which will further develop into a fetus.

Fishes are oviparous organisms. This means that they do not give birth to young fishes, instead, they lay eggs which further develop into young fishes.

The eggs that they lay are unfertilized. The female fishes lay unfertilized eggs and the male fishes produce sperms. Both these gametes float in water. When a sperm comes in contact with the eggs, there is a fusion of nuclei between the two. Hence fertilization occurs. As this fertilization takes place outside the body of the organism, it is called external fertilization.

a.

b. After the embryo gets implanted in the maternal uterus, it’s gradual development continues. Body parts such as hands, legs, head, etc. develop and the resultant fetus starts to resemble the adult human beings in terms of body parts and structure.

When the development of the fetus is complete, the mother delivers the baby, i.e. the fetus is expelled out from the mother's body.

Hens and frogs are both oviparous, but their mechanisms of fertilization are different. Hen exhibits internal fertilization, whereas a frog exhibits external fertilization.

The eggs that hens lay are fertilized eggs. This means that the fusion of male and female gametes has already taken place inside the body of an organism. The development is in the embryo stage in the egg, and further development from embryo to chick takes place outside.

The eggs that frogs lay are unfertilized eggs. These eggs get fertilized when a sperm floating in water, comes in contact with them and their nuclei fuse. Thus, the fertilized takes place outside the body of an organism. Hence, it is external fertilization.

This is how the hens and frogs differ in fertilized methods.

(i) The stages are as follows:

a. Embedding of the embryo in the uterus of the mother, i.e. implantation.

b. Fusion of male and female gametes, i.e. fertilization.

c. Formation of the zygote and it’s development into an embryo as it travels from oviducts to uterus.

d. Fusion of nuclei during fertilization, in a zygote.

(ii) The correct sequence of these stages would be :

1. b. Fusion of male and female gametes, i.e. fertilization.

2. d. Fusion of nuclei of two gametes in a zygote.

3. c. Development of a zygote to an embryo as it travels down the oviducts to reach the uterus.

4. a. Embedding of the embryo in uterine walls of the mother, i.e. implantation.

Thus, the correct sequence would be: b, d, c, a.

(iii) During fertilization, the male gamete sperm reaches up to the female gamete, ovum or the egg cell. One of the sperms that reach the ovum, releases its nuclei into the egg cell. Then, inside the egg cell, or the zygote, takes place the fusion of nucleus of that sperm with the nucleus of the female gamete. Thus, the product of fertilization, the zygote is formed. The rest of the sperm degenerates.