Class 10 Science Reproduction Exam Notes

Class 10 Science Reproduction Exam Notes. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

Class 10 Science: Reproduction Exam Notes

The ability of living organisms to produce new living beings similar to themselves is called reproduction.

Types of Reproduction

ASEXUAL REPRODUCTION

A single organism commonly multiplies through asexual reproduction. Asexual reproduction is the process of formation of new individuals from specialised or unspecialised parts of a single parent without the formation and fusion of gametes. Because new individuals are formed from a single parent, asexual reproduction is called uniparental.

Fission (L. fissus – cleft): It is a mode of asexual reproduction in which a parent undergoes division to form two or more individuals. Fission is of two types: binary fission and multiple fission.

Binary fission: It means ‘splitting into two’. In binary fission, the nucleus or nuclear matter elongates and then divides into two. It is followed by cleavage of the cytoplasm in between the two daughter nuclei to form two daughter individuals. Example: Amoeba.

Methods of Asexual Reproduction

Multiple fission: In multiple fission, many individuals are formed from a single individual.

• The nucleus of the cell divides repeatedly, producing many nuclei.
• Each nucleus is surrounded by a small amount of cytoplasm and many daughter cells are produced within a cyst (protective wall).
• The cyst breaks up under favourable conditions and the small offspring are liberated.
• In plants, multiple fission is seen in many algae, and in animals a common example is the malarial parasite (Plasmodium).

Budding: 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.

• The nucleus of the parent divides and one of the daughter nuclei passes into the bud.
• The bud detaches itself from the parent body and becomes a new individual after growing to full size.
• In plants, budding takes place in yeast, and in animals budding is seen in Hydra and sponges.

Spore formation: In spore formation, the parent plant produces hundreds of tiny spores which can then produce new plants. During the growth of a fungus like Rhizopus, a tiny round bulb-like structure called the sporangium develops at the top of the hyphae. In non-flowering plants like fungi (Mucor, Rhizopus, Penicillium), bacteria, ferns or mosses, formation of spores is a method of reproduction.

Regeneration: It is the ability of an organism to replace its lost body parts. Hydra, Planaria and sponges exhibit regeneration. A special case of regeneration is fragmentation, in which a parent multicellular organism on maturing breaks up naturally to produce two or more daughter organisms. Among plants, filamentous algae like Spirogyra reproduce by this method.

Fragmentation (L. fragmere – to break): It is the process of breaking up of the body of an organism into two or more parts called fragments, each of which grows into a new individual. Fragmentation is quite common in algae, fungi, bryophytes and some marine ribbon worms. It is caused by mechanical disturbance, chemicals, death and decay of older parts, emptying of intervening cells, etc. Fragmentation is a common method of multiplication in the green filamentous alga Spirogyra. Here all the cells are capable of photosynthesis, growth and division. Therefore, each fragment grows into a new filament.

Vegetative propagation: In vegetative propagation, new plants are obtained from parts of old plants like stems, roots and leaves, without the help of any reproductive organs (flowers and seeds). It can be achieved naturally or artificially. There are two ways of vegetative propagation.

(a) Natural vegetative propagation: The structures that take part in this type of reproduction are roots, stems and leaves.

• By roots: In some plants like dahlia and sweet potato, the adventitious roots become thick, swollen and tuberous due to storage of food.
• By stems: Some plants reproduce by means of stems. They may be aerial, like runners and suckers, or underground, like ginger (rhizome), potato (tuber) and sugarcane.
• By leaves: The fleshy leaves of Bryophyllum bear adventitious buds in the notches along the leaf margin.

(b) Artificial vegetative propagation: Some plant growers have developed artificial methods of vegetative propagation, like cutting, layering and grafting, which are used in agriculture and horticulture.

SEXUAL REPRODUCTION

Sexual reproduction is a mode of multiplication in which the young ones are produced through the process of formation and fusion of gametes.

Significance of sexual reproduction:

• Variation: Due to reshuffling of chromosomes and crossing over, sexual reproduction brings about variations in almost all characters, so that no two individuals are similar.
• Vigour and vitality: It maintains the vigour and vitality of the individuals.
• Uniformity of population: Due to the flow of genes amongst individuals during sexual reproduction, the uniformity of the population is maintained, where there is a broad resemblance of all individuals with one another.
• Evolution: Genetic changes brought about by sexual reproduction play an important part in the evolution of new forms.

Sexual reproduction in flowering plants: A flower has the following parts.

• Sepals: Sepals are green, outermost, leaf-like floral organs which protect the flower in the bud stage. In the mature stage they provide support to the other floral organs.
• Petals: Petals are coloured accessory floral organs which lie above the sepals. Petals attract insects to flowers for pollination.
• Stamens: Stamens are the male reproductive organs of the flower. Each stamen has a slender stalk called the filament. Each anther lobe has two long pollen sacs, so there are four pollen sacs in an anther. They produce a yellowish powder of haploid pollen grains.
• Carpels: Carpels form the central female reproductive organs of the flower.

Pollination

Pollen grains from the anther are transferred by air, water, insects and other animals to the stigma of a pistil. “The process of transfer of pollen grains from the anther of a flower to the stigma of the same or another flower is called pollination.” On the basis of the transfer of pollen grains to the stigma of the same or another flower, pollination is of two types: (A) self-pollination and (B) cross-pollination.

Self-pollination: The process of transfer of pollen grains from the anther of a flower to the stigma of the same flower is called self-pollination or autogamy. Examples: pea, China rose, rice, wheat.

• Self-pollination in bisexual flowers ensures continuity of the race.
• It helps to preserve the parental characters, as the gametes from the same flower are involved.

Cross-pollination: The process of transfer of pollen grains from the anther of a flower to the stigma of another flower is called cross-pollination or allogamy. Examples: mustard, rose.

• Seeds produced by cross-pollination have much better germinating capacity.
• Variations are introduced by cross-pollination.

Fertilisation in Plants

• Pollination is followed by fertilisation in plants.
• After reaching the stigma, the pollen grain develops the pollen tube.
• This pollen tube grows through the style and reaches the ovary where the ovules are located.
• The pollen tube enters the ovule through a small opening called the micropyle, where it releases two male gametes into the embryo sac.
• One male gamete fuses with the egg contained in the embryo sac of the ovule; this fusion of male and female gametes is called syngamy and its product is the zygote.
• The other male gamete fuses with the two polar nuclei and this process is called triple fusion, in which three nuclei (one male gamete and two polar nuclei) are involved.
• The process of double fertilisation occurs inside each embryo sac, in which two fusions, syngamy and triple fusion, take place.
• After fertilisation, the ovary develops into the fruit and the ovules develop into the seeds.

Reproduction in Humans

Male reproductive system: The human male reproductive system consists of the following organs: a pair of testes, epididymis, vas deferens, seminal vesicles, ejaculatory duct, prostate gland, urethra and penis.

• A pair of testes lies in a small sac-like muscular structure outside the abdominal cavity called the scrotum. The function of the testis is to produce sperms and the male sex hormone called testosterone. The scrotum provides the optimal temperature for the formation of sperms.
• The epididymis is a coiled tube-like structure firmly attached to the testis and serves as the storehouse of sperms. Inside the epididymis, sperms mature and develop motility.
• Vas deferens: The sperms are carried by a long tube called the vas deferens or sperm duct into organs called seminal vesicles, where the sperms get nourished and stored.
• The seminal vesicle is a glandular structure which joins the vas deferens to form the ejaculatory duct.
• The ejaculatory duct enters the prostate gland and joins the urethra to form the common urino-genital duct.
• The penis is a copulatory organ at the tip of which the urino-genital duct opens.

Female reproductive system: The human female reproductive system consists of the following organs: a pair of ovaries, fallopian tubes (oviducts), uterus (womb), cervix and vagina.

• Ovaries are a pair of small, oval-shaped organs located in the abdominal cavity near the kidney. They are the female primary reproductive organs which perform the dual functions of production of the female gamete or ovum and secretion of the female sex hormones, oestrogen and progesterone.
• Fallopian tube or oviduct: A pair of long convoluted tubes that carry the ovum or egg from the ovary to the uterus. The fallopian tube has a funnel-shaped opening near the ovary. The tubes from both sides open into a muscular structure, the uterus.
• Uterus or womb: A hollow, pear-shaped organ within which the embryo develops. Its upper portion is broader, while its lower, narrower portion is called the cervix.
• Vagina: The cervix opens into the vagina, which is a tubular structure also called the ‘birth canal’ or the canal for menstrual flow. The vagina receives sperms from the male and also serves as the passage through which the fully developed foetus is born.

MENSTRUAL CYCLE

If the egg is not fertilised, it lives for one day and is then expelled. This sets in motion what is called the menstrual or ovarian cycle. The first menstruation is called menarche. It stops between the ages of 45 and 50 years. Permanent stoppage of menstruation is called menopause. The menstrual cycle consists of four phases.

• Menstrual phase: It is characterised by menstruation (= menses, Gk. mensum – month), i.e. the discharge of blood, mucus and endometrial lining. The menstrual phase lasts for 3–5 days.
• Proliferative phase: There is repair and growth of the endometrium. Under the influence of the hormone FSH, a few follicles grow, but only one follicle, called the Graafian follicle, matures in the two ovaries. It secretes the hormone oestrogen. The proliferative phase lasts from the 5th to the 14th day.
• Ovulation phase: At about the middle of the menstrual cycle, on the 13th or 14th day, the growing follicle bursts and the mature ovum is released from the ovary under the influence of oestrogen and LH.
• Secretory phase: It lasts from the middle of the cycle to its end, i.e. 14–28 days. During this period the uterine wall thickens further. Glands present in the endometrial area become functional and begin to secrete materials for the nourishment of the egg if it happens to get fertilised.

REPRODUCTIVE HEALTH

Reproductive health is the state of physical, mental and social fitness to lead a responsible, safe and satisfying reproductive life.

1. It provides awareness to both male and female regarding fertility-regulating methods.
2. Reduction in the number of children to the limit of enjoying family life as well as rearing the children with better resources as and when they are available.
3. Prevention of sexually transmitted diseases.
4. Management of disorders related to the reproductive system by getting them treated at the earliest.

CONTRACEPTION

Prevention of pregnancy is called contraception. The techniques used in preventing the occurrence of pregnancy are called contraceptive devices.

Mechanical barrier methods of contraception:

• Condom: It is a tubular latex sheath which is worn over the male copulatory organ (penis) during sex.
• Cervical cap: It is a rubber cap that is fitted over the cervix.
• Diaphragm: It is a dome-shaped rubber cap with a flexible metal or spring ring at the margin, which is fitted inside the vagina.
• Intrauterine contraceptive devices (IUCD or IUD): They are devices made of plastic, metal or a combination of the two, which are inserted into the uterus to prevent pregnancy, generally through excessive secretion of cervical mucus. The most common type is copper, which prevents implantation. It is functional for 3–5 years.

Hormonal methods of contraception:

• Oral pills: They contain progesterone with or without oestrogen.
• Implants: They are subdermal devices which provide long-term contraception, e.g. Norplant.
• Morning-after pills: They prevent pregnancy even after coitus, e.g. i-pill.

Chemical methods of contraception: They are creams, jellies and foaming tablets (vaginal pills) which are placed in the vagina for killing the sperms at the time of coitus.

Surgical methods (sterilisation): They are of two types: vasectomy in males and tubectomy in females.

• Vasectomy: The two vasa deferentia of the male are blocked by cutting a small piece and tying the rest. This prevents the passage of sperms from the testes into the semen.
• Tubectomy: A portion of both fallopian tubes is excised or ligated to block the passage of the ovum.