How do Organisms Reproduce Class 10 – Continuing our series for Class 10 Revision for CBSE board exams, we bring you a new chapter today i.e. How do organisms reproduce Class 10.
Let us now understand this chapter’s weightage. In previous years, questions of 1, 2, 3 as well as 5 marks have been asked from this chapter.
Make sure that you read this from NCERT to score well in 1 and 2 mark questions and practice drawing diagrams once before the exam.
The concepts that are going to be discussed in this article are:
- Role of DNA in reproduction
- Sexual and asexual reproduction
- Modes of asexual reproduction
- Vegetative propagation
- Spore formation
- Sexual reproduction in flowering plants
- Sexual reproduction in Human Beings
- Male reproductive system
- Female reproductive system
- Reproductive health
Let’s discuss each topic of How do Organisms Reproduce Class 10 one-by-one
Role of DNA in reproduction:
We know that production of new organisms from existing organisms of the same species is known as reproduction. DNA plays an important role in this, because chromosomes present in the nucleus of a cell contains information to be transferred to offspring, in the form of DNA. This DNA in cell nucleus is the information source for making proteins, which perform a lot of important functions in our body.
Therefore, a very important event in our body is the creation of DNA copy. From a single DNA, a copy is made, which then has to be separated, although this again is a very complicated process. Effectively, a cell has to divide to give rise to two cells.
These cells end up having some variations, thus the DNA copies generated are not identical with the original one. These variations can or cannot be harmful.
In some cases, these variations are important, as they can give them a chance to survive when environmental changes take place.
Sexual and asexual reproduction:
In asexual mode of reproduction, the offspring arises from a single parent, without the involvement of gametes or sex cells.
However, in sexual reproduction, the offspring arises from two parents of different sexes, by combination of their gametes.
We will study both these in detail, one by one.
Modes of asexual reproduction:
- Fission: Many single-celled organisms simply split or break into 2 identical halves, leading to the creation of two new organisms. This is called fission. For example, Amoeba, some protozoa and bacteria.However, some single-celled organisms divide into many daughter cells simultaneously, rather than just 2. This is called multiple fission and is shown by Plasmodium. Some Important Diagrams:
- Fragmentation – Now, some multi-cellular organisms with simpler body design also have the ability to simply divide in 2 parts, where each part gives rise to a complete organism. For example, Spirogyra
- Regeneration – In many multi-cellular organisms, it is observed that some body parts can give rise to new complete organisms. For example, Planaria can be cut into any number of pieces, and each piece gives rise to a new individual, as seen in the diagram below:
- Budding – in budding, a small part of the of the parent’s body grows out as a bud, which then detaches and becomes a new organism. For example, it takes place in Hydra.
- Vegetative propagation – This method occurs in plants. In this method, new plants are obtained from the parts of old plant (like stems, roots and leaves). This is used for reproducing plants like sugarcane, rose, etc. the advantage of using this method is that plants obtained by this method bear fruits earlier, and we can also reproduce the plants that have lost the ability to produce seeds.
- Spore formation – In this method, the parent plant produces hundreds of microscopic reproductive units called ‘spores’. When these spores spread in air, they land on food or soil or such a substance and under favourable conditions, these germinate and produce new organisms. For example, Rhizopus.
Sexual reproduction in flowering plants
Main parts of a flower are sepals, petals, stamens and carpel. Out of this, stamen and carpel are the reproductive parts.
Stamen – male reproductive part and it produces pollen grains
Carpel – female reproductive part and is present in middle of the flower. It in turn consists of three parts – swollen bottom part (ovary), middle elongated part (style) and terminal sticky part (stigma)
Ovary contains ovule – each ovule has an egg cell
Fusion of this female egg cell with male egg cell gives the zygote, which is eventually gives rise to a new plant. This process of fusion is called fertilization.
Now for this fusion to occur, pollen has to reach the ovary. For this, a tube grows out of the pollen grain and travels through the style to reach the ovary.
After fertilization, zygote undergoes repeated division to form an embryo. The ovule is finally converted into a seed. It contains the future plant, which develops under suitable conditions and the process is called germination.
Ovary grows and turns into a fruit
Meanwhile, petals, sepals, stamens, etc fall off.
Sexual reproduction in humans
You must have observed that when a child is small, it becomes difficult to distinguish from appearance whether the child is a boy or a girl.
But as we grow, changes start taking place in the body. These changes have been summarised below:
The period during which adolescent boys and girls reach sexual maturity and become capable of reproduction is called puberty.
|Changes that take place in boys during puberty
|Changes that take place in girls during puberty
Let us now look at Male Reproductive System.
The male reproductive system consists of parts that make the germ cells, and parts that deliver them to the site of fertilization.
The male sex-cells are sperms, that are tiny bodies that consist of mainly genetic material and a long tail that helps them to move towards the female germ-cell.
- The formation of germ cells or sperms takes place in testes, which are located outside the abdominal cavity in scrotum.
- The sperms formed are delivered through the vas deferens.
- Along this path, glands like the prostate and the seminal vesicles add their secretions to provide the sperms a fluid medium to travel.
Female Reproductive System –
- The female germ-cells are made in the ovaries. After maturation,one egg is produced every month by one of the ovaries.
- The egg is carried from the ovary to the womb through the fallopian tube.
- The two oviducts unite into the uterus.
- The uterus opens into the vagina through the cervix.
Let us now study how fertilisation takes place.
For fertilization to happen, male egg has to fuse with female egg cell. This is done in the following manner:
- The sperms from the male enter through the vaginal passage during sexual intercourse.
- They travel upwards and reach the oviduct where they may encounter the egg.
- The cells fuse together, and the fertilised egg, the zygote, gets implanted in the lining of the uterus, and starts dividing.
- The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. It provides a large surface area for glucose and oxygen to pass from the mother to the embryo and waste substances to pass from embryo to mother.
- The child develops inside mother’s body and is born as a result of rhythmic contractions of the muscles in the uterus.
Now, have you wondered what happens if fertilization does not take place!?
We saw that the ovary releases one egg every month. Thus, the uterus also prepares itself every month to receive a fertilised egg. Its lining becomes thick and spongy for this purpose.
This would be required for nourishing the embryo if fertilisation had taken place.
Now, however, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.
We all know that our country’s population is increasing day by day, and this creates problem as we have a limited number of resources. Therefore, birth control methods are being actively spread today. Not only this, unsafe sexual act can also lead to many diseases, called sexually transmitted diseases. You can now see these and some birth control methods on your screen now.
Sexually Transmitted Diseases (STD):
- Gonorrhoea (caused by bacteria)
- Syphilis (caused by bacteria)
- AIDS (Acquired Immune Deficiency Syndrome) (caused by virus, HIV)
Birth control methods:
- Barrier methods – this involves condoms, diaphragms. These devices prevent sperm from meeting the ovum
- Chemical methods – females can use 2 types of pills – oral pills and vaginal pills. Both of these help in avoiding pregnancy
- Intra-uterine Contraceptive Devices – example copper-T. It is placed inside woman’s uterus and prevents implantation of fertilized egg in her uterus
- Surgical methods – in males, this process is called ‘vasectomy’ and involves removal and then tying up a part of vas deferens. In females, it is called ‘tubectomy’ and involves removal and tying up of a small portion of oviducts.