How do organism reproduce is a most important chapter for (Class 10 Science Chapter 8). Here you will get all important topics such as : Types of asexual reproduction, male reproductive system, female reproductive system and much more…
LIST OF TOPICS
- INTRODUCTION OF REPRODUCTION
- ASEXUAL REPRODUCTION AND ITS TYPES : FISSION, FRAGMENTATION, REGENERATION, SPORE FORMATION, VEGETATIVE PROPAGATION AND TISSUE CULTURE
- SEXUAL REPRODUCTION IN PLANTS
- MALE REPRODUCTIVE SYSTEM
- FEMALE REPRODUCTIVE SYSTEM
- FERTILISING AND NON FERTILISING EVENT
- MENSTRUAL CYCLE
- CONTRACEPTION METHODS
The production of new organisms from the existing organisms of the same species is known as reproduction.
- Reproduction is the creation of new living things.
- Reproduction is essential for the survival of a species on this earth.
- The process of reproduction ensures continuity of life on earth.
- Reproduction by human beings ensures that the human species will continue to exist on this earth for all the time to come.
- Reproduction gives rise to more organisms with the same basic characteristics as their parents.
There are two main methods of reproduction in living organisms:
- Asexual reproduction.
- Sexual reproduction.
New living organisms (new plants and animals) can be made either by the method of asexual reproduction or by the method of sexual reproduction.
The production of a new organism from a single parent without the involvement of sex cells (or gametes) is called asexual reproduction. It is called asexual reproduction because it does not use special cells called ‘sex cells’ (or gametes) for producing a new organism.
Some of the examples of asexual reproduction are: binary fission in Amoeba, budding in Hydra, spore formation in Rhizopus (fungus), regeneration in planaria (flatworm), fragmentation in spirogyra and vegetative propagation in flowering plants(like rose plants).
- Asexual reproduction is the simplest method of reproduction. Actually, asexual reproduction takes place in unicellular animals and plants micro organisms (like bacteria) and simple multicellular animals (like Hydra and planaria) and some multicellular plants (like Bryophyllum, rose Plants, etc).
The production of a new organism from two parents by making use of their sex cells (or gametes) is called sexual reproduction.
- The two parents which are involved in sexual reproduction are called male and female. Our father is a male and our mother is a female. The male and female parents have special organs in them which produce male sex cells and female sex cells respectively (which are required in sexual reproduction). The humans, fish, frogs, cats and dogs all reproduce by the method of sexual reproduction. Most of the flowering Plants also reproduce by sexual reproduction.
In the process of fission, a unicellular organism splits to form two (or more) new organisms. Fission is of two type’s binary fission and multiple fission depending on whether the parent organism splits to form two new organisms or more than two organisms.
- BINARY FISSION Binary fission is an asexual method of reproduction of organisms. In binary fission, the parent organism splits to form two new organisms. The unicellular organisms like Amoeba, Paramecium, Leishmania, bacteria, etc reproduce by binary fission. Paramecium is a unicellular animal. Paramecium also reproduces by the method of binary fission. Leishmania is a unicellular animal (which is a protozoan). It is a parasite which causes the disease known as kala–azar. Leishmania has a greater degree of organization in its body. Leishmania reproduces by the process of binary fission.
- MULTIPLE FISSION Multiple fission is also an asexual method of reproduction in organisms. In multiple fission, the parent organism splits (Or divides) to form many new organisms at the same time.
Budding is an asexual method of reproduction. In budding, a small part of the body of the parent organism grows out as a bud, which then detaches and becomes a new organism.
- Hydra is a simple multicellular animal. Hydra reproduces by the process of budding by using its regenerative cells. In Hydra, first a small outgrowth called bud is formed on the side of its body by the repeated mitotic divisions of its cells. This bud then grows gradually to form a small Hydra by developing a mouth and tentacles. And finally the tiny new Hydra detaches itself from the body of parent Hydra and lives as a separate organism.
- Yeast is tiny, unicellular, non-green plant (which is a fungus). Yeast reproduces by budding.
In spore formation, the parent plant produces hundreds of microscopic reproductive units called spores. When the spore case of the plant bursts, then the spores spread into air. When these air – borne spores land on food (or soil) under favorable conditions (like damp and warm conditions), they germinate and produce new plants.
- The spore formation method of asexual reproduction is used by unicellular organisms as well as by multicellular organisms. For example: Bacteria are the unicellular organisms which reproduce by spore formation whereas fungi such as Rhizopus (bread mould) and Mucor and non-flowering plants such as ferns and mosses are multicellular organisms which reproduce by the spore formation method.
The process of getting back a full organism from its body parts is called Regeneration. The simple animals like Hydra and planaria show regeneration.
- Planaria is a flatworm which is found in freshwater ponds and slow-moving streams. Planaria possesses great power of regeneration. If the body of planaria somehow gets cut into a number of pieces, then each body piece can regenerate into a complete planaria by growing all the missing parts.
- The regeneration of an organism from its cut body part occurs by the Process of growth and development.
- The organisms like planaria and Hydra are simple multicellular organism which can be regenerated from their cut body parts to form complete organisms.
The breaking up of the body of a simple multicellular organism into two (or more) pieces on maturing, each of which subsequently grows to form a complete new organism, is called fragmentation. The organisms like Spirogyra and Sea anemones can reproduce by the method of fragmentation.
- Spirogyra reproduces by the asexual method of fragmentation.
The main difference between fission and fragmentation is that in fission, a unicellular organism breaks up to form two (or more) daughter organisms. whereas in fragmentation, a multicellular organism breaks up to form two (or more) daughter organisms.
In vegetative propagation, new plants are obtained from the parts of old Plants (like stems, roots and leaves), without the help of any reproductive organs. The green grass grows in the fields after rains from the dry, old stems of grass plants present in the fields, by the method of vegetative propagation.
- Bryophyllum plants can be reproduced by vegetative propagation by using either a piece of its stem or its leaves.
- Money plant can also be grown by vegetative propagation by using a piece of its stem.
- A tuber is the thickened, underground stem of a plant which is swollen with stored food. The tuber has a number of buds (called eyes). Each bud (or eye) of the tuber grows into a new plant when the old tuber is planted in the soil in the next growing season. The example of tuber is potato.
- Potato tuber is an underground stem of the potato plant. Potato tuber can be used for the vegetative reproduction of potato plants.
The vegetative propagation method of producing potato plants by tubers is much faster than the production of potato plants from seeds. Some of the examples of the plants which can be reproduced by vegetative propagation are: Bryophyllum, Guava, Potato, Onion, Banana, Garlic, and Water hyacinth, Tulip, Mint, Strawberry and Lily.
Artificial Propagation of Plants
Cutting: A small part of a plant which is removed by making a cut with a sharp knife is called a cutting. The plants like rose, Bougainvillea, Chrysanthemum, grapes, sugarcane, bananas and cactus, etc can be grown by means of cuttings. For example rose plants.
Layering: In this method, a branch of the plant is pulled towards the ground and a Part of it is covered with moist soil leaving the tip of the branch exposed above the ground. After some time, new roots develop from the part of the branch buried in the soil. The branch is then cut off from the parent plant. The layering method is used for the propagation of plants like, Jasmine, Strawberry, and Raspberry, Lemon, Guava, Hibiscus (China rose), Bougainvillea and many slender ornamental plants
Grafting: Grafting is a method in which the cut stems of two different plants (one-with roots and other without roots) are joined together in such a way that the two stems join and grow as a single plant.
- Grafting is used to breed fruit trees and flowering bushes. Apple, peach, Apricot and pear trees are often grafted.
Advantages of the grafting method of artificial propagation:
- Grafting enables us to combine the most desirable characteristics of the two plants (scion and stock) in its flowers and fruits.
- It enables us to obtain flowers and fruits having different desired characteristics by grafting scions from different varieties of plants on the same stock. Many varieties of mango have been produced by grafting method.
Advantages of Artificial Vegetative Propagation
- The new plants produced by artificial vegetative propagation will be exactly like the parent plants. Any desirable features of the parent plant will be replicated in the new plants.
- The plants grown by vegetative propagation usually need less attention in their early years than the plants grown from seeds.
- Many plants can be grown from just one parent plant by artificial propagation.
- We can also get seedless plants by artificial propagation.
The production of new plants from a small piece of plant tissue (or cells) removed from the growing tips of a plant in a suitable growth medium (called culture medium) is called tissue culture.
- The tissue culture technique is being used increasingly for the production of ornamental plants like Orchids, Dahlia, Carnation, Chrysanthemum, etc. The production of plants by the method of tissue culture is also known as micro propagation.
Advantages of Tissue Culture
- Tissue culture is a very fast technique. Thousands of plantlets can be produced in a few weeks from a small amount of plant tissue.
- The new plants produced by tissue culture are disease free.
- Tissue culture can grow plants round the year, irrespective of weather or season.
Do Organisms Create Exact Copies of Themselves In Asexual Reproduction
Asexual reproduction usually results in the production of genetically identical offspring’s; the only genetic variation arises as a result of occasional inaccuracies in DNA replication (or DNA copying) at the time of cell division.
The material which carries genetic information from the parents to the offspring is DNA- Deoxyribo Nucleic Acid (which is present in the form of chromosomes in the nuclei of all the cells) the basis of asexual reproduction is mitosis. This is the division of a nucleus into two identical daughter nuclei. Each daughter nucleus has the same genetic makeup because of the replication of DNA (or copying of DNA) of the parent cell. After the division of the nucleus, the rest parent cell divides to form two genetically identical daughter cells. The daughter cells can then form two offspring. From this we conclude that all the offspring’s produced by one parent as a result of asexual reproduction are usually genetically identical.
- The importance of variations in organisms introduced during reproduction is that it helps the species of various organisms to survive and flourish even in adverse environment. This will become clear from the following discussion. There may be some drastic changes like excessive heat or cold or shortage of water (drought) etc. in the habitat of a species of organisms.
Sexual reproduction takes place by the combination of special reproductive cells called sex cells. Sex cells are of two types, male sex cells and female sex cells (which come from two different parents a male and a female). The sex cells are commonly known as gametes. Thus the cells involved in sexual reproduction are called gametes.
In sexual reproduction, a male gamete fuses with a female gamete to form a new cell called zygote. This zygote then grows and develops into a new organism in due course of time. The sex cells or gametes are also sometimes called germ cells and there are two types of germ cells, male germ cells and female germ cells.
The sexual reproduction in plants takes place in the following steps
- The male organ of flower called stamen, makes the male gametes (male sex cells) of the plant. These male gametes are present in pollen grains.
- The male gametes present in pollen grains fertilize the female gametes or egg cells present in ovules.
- The fertilized egg cells grow within ovules and become seeds.
- The seeds produce new plants on germination under suitable conditions of water, warmth, air and light etc.
The main parts of a flower are receptacle, sepals, petals, stamen and carpel. The flowers which contain only one sex organ, either stamens or carpals, are called unisexual flowers. The flowers of papaya and watermelon plants are Unisexual flowers. On the other hand, the flowers which contain the sex organs, stamens as well as carpel, are called bisexual flowers. The flowers of Hibiscus and mustard plants are bisexual flowers.
A new seed of the plant is formed when the male gamete present in a pollen Grain unites with the female gamete present in the ovule.
The transfer of pollen grains from the anther of a stamen to the stigma of a carpel is called pollination.
- When the pollen grains from the anther of a flower are transferred to the stigma of the same flower (or another flower on the same plant).it is called Self-pollination.
- When the pollen grains from the anther of a flower on one plant are transferred to the stigma of a flower on another similar plant, it is called cross-pollination.
Fertilization occurs when the male gamete present in pollen grain join with the female gamete (or egg) present in ovule.
Formation of Fruits and seeds
The fertilized egg (or zygote) divides several times to form an embryo within the ovule. The ovule develops a tough coat around it and is gradually converted into a seed (containing the baby plant). In fact, all the eggs in the ovules present in the ovary of a flower get fertilized by male gametes (from pollen) grains and grow to become seeds. The ovary of flower develops and becomes a fruit (with seeds inside it).
The other parts of flower like sepals, petals, stamens, stigma and style dry up and fall off. Only the ovary is left behind. So at the place on plant where we had a flower originally, we now have a fruit. (Which is the ovary of the flower containing seeds)? A fruit protects the seeds. Some fruits are soft, sweet and juicy like mangoes and oranges. But some fruits are hard, dry and woody like the peanuts and almonds, etc.
- A seed is the reproductive unit of a plant (which can be used to grow a new plant. The seed contains a baby plant (or embryo) and food for the baby plant.
- The part of baby plant in seed which develops into shoot with leaves is called Plumule and the part which develops into root is called radical.
- The part of seed which contains stored food for the baby plant is called cotyledons. The wheat Grains, gram (chana), corn, peas and beans, are all seeds. The baby plant present inside a seed is in the inactive state (called dormant state).
- When the seed get suitable conditions like water, air and warmth etc, it germinates and a new plant grows out of the seed. In this way the parent plant reproduces more plants like itself by forming seeds through flowers.
SEXUAL REPRODUCTION IN ANIMALS
An animal having male sex cells that called sperms, in its body is called male. On the Other hand, an animal having female sex cells called ova (or eggs) in its body is called female.
Sexual reproduction takes place by the combination of special reproductive cells called sex cells. These sex cells are also known by another name which is gamete. The cells involved in sexual reproduction are called gametes.
- Gametes are of two types: male gametes and female gametes. The male gamete in animals is called sperm, and the female gamete in animals is called ovum, or egg. Sperms and ova (or eggs) are extremely small cells which can be seen only with the help of a high power microscope. The ovum or egg contains water and stored food. The sperms are motile which can move independently with the help of their tails. Fusion of gametes gives rise to a single cell called zygote.
- We can also say that the cell which is formed by the fusion of a male gamete and a female gamete Is called zygote. In most simple words, zygote is a fertilized ovum. The process of fusion of gametes is called fertilization.
The fusion of a male gamete with a female gamete to form a zygote during the sexual reproduction is called fertilization.
- The stage of development between the zygote (fertilized egg) and the new formed baby is called embryo.
- Two modes of fertilization in animals are internal fertilization and external fertilization.
The fertilization which occurs inside the female body is called internal fertilization.
In internal fertilization, the female animal’s eggs are fertilized by sperms inside her body. In mammals (including human beings), birds and reptiles, the fertilization occurs inside the female body. The fertilization which occurs outside the female body is called external Fertilization.
In external fertilization, the female animal’s eggs are fertilized by sperms outside its body. In amphibians (like frogs and toads) and fishes, the fertilization of eggs occurs outside the female animal’s body. In other words, in amphibians (like frogs and toads) and fishes, external fertilization takes place.
The Advantages of Sexual Reproduction
Sexual reproduction leads to a greater variety in population. Sexual reproduction promotes diversity of characters in the offspring by providing genetic variation.
- Sexual reproduction plays an important role in the origin of new species having different characteristics. Genetic variation leads to the continuous evolution of various species to form better and still better organisms.
The sexual reproduction in animals takes place in the following steps
- The male parent produces male gametes (male sex cells) called sperms. The sperm is a small cell with a long tail (flagellum) for movement.
- The female parent produces female gametes (female sex cells) called ova (or egg).The ovum (or egg) is a much bigger cell than the sperm, having a lot of cytoplasm.
- The sperm enters into the ovum (or egg) and fuses with it to form a new cell called zygote .This process are called fertilization. So the zygote is a fertilized ovum (or fertilized egg).
- The zygote then divides again and again to form a large number of cells all of which remain together) and ultimately zygote grows and develops to become a new body.
The whole process of sexual reproduction in animals involves the formation of sperms and eggs, joining together of sperm and egg to form a zygote, and then the growth of zygote to form a baby animal.
The age at which the sex hormones (or gametes) begin to be produced and the generally boys attain puberty at the age of 13 to 14 years. While girls reach puberty at a comparatively lower age of 10 to 12 years. On attaining puberty the male gonads called testes, start producing male gametes called sperms and the female gonads called ovaries start producing female gametes called Ova (or eggs). In addition to producing sex cells (or gametes) male and female gonads (testes and ovaries) also produce and secrete sex hormones with the onset of puberty.
The testes produce the male sex hormone called testosterone, and the ovaries produce two female sex hormones, estrogen and progesterone. The sex hormones play an important role in the process of reproduction because they make the reproductive organs to mature and start functioning.
Puberty is the age at which the reproductive organs reach maturity and secondary sexual characteristics develop.
- The various changes which occur in boys at puberty are: hair growth under armpits and in pubic regions (genital area) between the thighs. Hair also grows on other parts of the body like hips and thighs.
- Fallopian tubes, uterus and vagina enlarge. Ovaries start to release eggs. Menstruation (monthly periods) start. Feelings and sexual drives associated with adulthood begin to develop. All these changes in Girls are brought about by the female sex hormones estrogen and progesterone made in ovaries.
A man has two testes. Testes are the primary reproductive organs in man. The sperms formed in testes come out and go into a coiled tube called epididymis. The sperms get stored temporarily in epididymis. From epididymis, the sperms are carried by a long tube called vas deferens which joins with another tube called urethra coming from the bladder Along the path of vas deferens, the glands called seminal vesicles and prostate gland add their secretions to sperms so that the sperms are now in a liquid .This liquid plus the sperms, it contains is called semen (which is a thick liquid). The secretions of seminal vesicles and prostate gland provide nutrition to the sperms and also make their further transport easier.
Urethra forms a common passage for sperms and urine. Urethra carries the sperms to an organ called penis which opens outside the body. The penis passes the sperms from the man’s body into vagina in the woman’s body during mating for the purpose of reproduction. In man (or human male) there is only one opening for the urine and sperms to pass out of the body.
A woman has two ovaries. Ovaries are the primary reproductive organs in a woman (or female).The function of ovaries are to make mature female sex cells (or female gametes) called ova or eggs, and also to make the female sex hormones (called oestrogen and progesterone). Each ovary is composed of several thousand follicles (which are a kind of unripe eggs or unripe ova. The two oviducts connect to a bag like organ called uterus (or womb) at their other ends. The growth and development of a fertilized ovum (or fertilized egg) into a baby takes place in the uterus. The uterus is connected through a narrow opening called cervix to another tube called vagina which opens to the outside of the body. Vagina receives the penis for putting sperms in to the woman’s body.
Vagina is a tubular structure. Vagina is also called birth canal because it is through this passage that the baby is born after the completion of development inside the uterus of the mother. In woman (or human female) the opening for passing out urine (called urethra) and the vaginal opening are separate. The complexity in structure and function of the female reproductive system is necessary for the union of sperms and ovum (or eggs) inside the female body and the development of the baby in the mother’s uterus.
Fertilisation in human
In human beings internal fertilization takes place. The sperms (or male gametes) made in the testes of man are introduced into the vagina of the woman through penis during copulation (or mating).In this way, millions of sperms are released into the vagina at one time. The sperms are highly active and mobile. The sperms move up through cervix into the uterus. From uterus, the sperms pass into the oviducts. One of the oviducts contains an ovum (or egg cell) released by the ovary during Ovulation. Only one sperm fuses with the ovum in the oviduct to form a zygote. This is called fertilization. Thus, the fertilization of the ovum takes place in the oviduct. When the ovum (or egg) is fertilized in the oviduct, then a zygote is formed. The zygote divides rapidly by mitosis as it moves down slowly in the oviduct and forms a hollow ball of hundreds of cells. This hollow ball of cells, now called an embryo, sinks into the soft and thick lining of the uterus and gets embedded in it. The embedding of embryo in the thick lining of the uterus is called implantation.
After implantation, a disc-like special tissue develops between the uterus wall and the embryo, which is called placenta. The foetus is connected to placenta in Mother’s body through umbilical cord. It is through the placenta that all the requirements of the developing foetus like nutrition, respiration, and excretion etc, are met from the mother’s body. In other words, the exchange of nutrients, oxygen and waste products between the embryo and the mother takes place through the placenta.
- The time period from the fertilization up to the birth of the baby is called gestation.
The average gestation period in humans (or the average duration of human Pregnancy) is about nine months. During the gestation pe0riod, the fetus grows to become a baby. Birth begins when the strong muscles in the walls of the uterus start to contract rhythmically. The rhythmic contraction of uterus muscles gradually pushes the baby out the mother’s body through vagina. This is how a baby is born.
The population of our country is increasing rapidly day by day. Though our country has sufficient food resources but still many people do not get sufficient Food for their large families due to poverty. So every year it is becoming very difficult for our Government to provide sufficient food, adequate clothing, good housing and proper education to every citizen of the country. It is therefore, very important for the couples who are in the reproductive stage of their life to control the size of their families by having fewer children by using family planning technique, birth control measures. Birth control can be done by preventing pregnancy in females.
Birth Control Methods
The prevention of pregnancy in women (by preventing fertilization) is called Contraception.
- Barrier methods.
- Chemical methods
- Surgical methods.
Condoms are used by males (by putting them as a covering on the penis). Diaphragm (or cap) is used by females (by putting it in the vagina to cover the cervix). Condom as well as diaphragm prevents the sperms to meeting the Ovum (or egg) by acting as a barrier between them. An important benefit in the Use of condom is that it protects a person from the sexually transmitted diseases such as gonorrhea, syphilis and AIDS.
Oral pills and vaginal pills, which are made of specific drugs. The oral pills contain hormones which stop the ovaries from releasing ovum into the oviduct Oral pills are also called oral contraceptives (written in short as OC).This is very effective Method of preventing pregnancy so long as the pills are taken at the right time Some women, experience unpleasant side effects on taking oral pills because they change the hormonal balance in the body. So it is important that the women on pills have regular check-ups with their doctor. The vaginal pills contain the chemicals called spermicides which kill the sperms.
INTRA-UTERINE CONTRACEPTIVE DEVICE (IUCD)
Contraceptive device called Copper-T is also very effective in preventing pregnancy. A copper-T is placed inside the uterus by a doctor or a trained nurse The IUCD or Copper –T prevents the implantation of fertilized egg in the uterus. If women use a Copper-T as a method of contraception for avoiding unwanted pregnancies, then Copper-T cannot protect her from acquiring sexually transmitted diseases.
In males, a small portion of the sperm duct is removed by surgical operation and both the cut ends are ligated (or tied) properly. This prevents the sperms from coming out. The surgical procedure carried out in male is called vasectomy. In females a small portion of the oviducts is removed by surgical operation and the cut ends are ligated. This prevents the ovum from entering into the oviducts. The surgical procedure carried out in females is called tubectomy.
Surgical operation can also be used for the termination of pregnancies in women particularly after eight weeks of conception. Such surgical termination of Pregnancy is allowed by law only in certain circumstances where the doctors decide that continuance of pregnancy can affect the health of mother or of unborn child.
Sexually Transmitted Diseases (STD)
The diseases which are spread by sexual contact with an infected person are called sexually transmitted diseases (or STD). Thus, a healthy person can get STD by making sexual contact with an infected person. Some of the common sexually transmitted diseases are.
- AIDS(Acquired Immune Deficiency Syndrome)
Gonorrhea and syphilis are caused by bacteria. The bacteria which cause these diseases spread through sexual contact with an infected person. The most common symptoms of the sexually transmitted diseases are burning Sensation at urination, passing of urethral discharge (containing pus) and sores in the genitals. Gonorrhea And syphilis are curable diseases. AIDS disease is caused by a virus called HIV (Human Immuno-deficiency virus). AIDS damages the body’s immune system so That the body becomes weak and cannot protect itself against infection. So AIDS is a very dangerous disease which leads to death. No definite cure has been found for the AIDS.