How do organisms Reproduce ||Science notes class-10th chapter-8

How to Organisms Reproduce

Science notes class-10th chapter-8

•Reproduction is the process by which living organisms produce new individuals similar to themselves. It ensures the continuity of life on earth.

•Nucleus of the cell contains DNA (deoxyribose nucleic Acid) which is the heredity material.

•DNA replicates and form new cells causing variation. So, this new cell will be similar but may not be identical to original cell.

•Variations are useful for the survival of the individual and species over time as well as basis for evolution.

Types of reproduction

(a)Asexual Reproduction

•A single individual give rise to new individual.

•Gametes are not Formed.

•New individual is identical to parent.

•It is extremely useful as a means of rapid multiplication.

•Adopted by lower organisms.

(b) Sexual Reproduction

•Two individuals I.e, one male and one female are needed to give rise to new individual.

•Gametes are formed.

•New individual is genetically similar but not identical to parents.

•It is useful to generate more variations in species.

•Adopted by higher organisms.

Mades of Asexual Reproduction

(I)Fission :The parent cell divides into daughter cells.

→Binary Fission:Two cells are formed Eg:Amoeba.

→Multiple Fission:Many cells are formed Eg:Plasmodium.

(ii)Fragmentation:The organism break -up into smaller pieces upon maturation, each piece develops into new individual Eg;spirogyra.

(iii)Regenration:If organism is somehow cut or broken into many pieces, each piece grows into a complete organism.Eg:Planaria, Hydra.

(iv)Budding:A bud is formed which develops into tiny individual.It detaches from parent body upon maturation and develops into new individual E.g;Hydra.

(v)Vegetative Propagation:In many plants , new plants develops from vegetative parts such as:

→By roots :Eg,dahilas, sweet potato.

→By stem:Eg, Patato, ginger.

→By leaves:Eg, bryophyllum(leaf notches bear buds which develop into plants).

→Artificial Methods.

(a)Grafting:Eg;Mango

(b)Cutting:Eg;Rose

(c)layering:Eg;Jasmine

(d)Tissue culture:

This is a technique of propagating plants by culturing cells or tissues in a culture medium.when vegetative propagation is not possible in a plant, its bud , shoot apex, or some other part is used for micro propagation. This is called explant.

Advantages of tissue culture

•It provides rapid propagation of identical individual.

•very small explants can be used for micropropagation.

•Usually the planets obtained are disease-free.

•It can be carried out throughout the year.

•plants can be grown even from sterile hybrids.

•Only a small space is required for tissue culture.

•Micropropagation is used for the propagation of disease-free Orchids, Gladioli, chrysanthemum, Carnations, Sugarcane and other Ornamental plants.

•An embryo which dies can be made to grow (embryo rescue).

Benefits of tissue culture:

•we can grow plants like banana, rose, jasmine etc.

•New plants are genetically similar to parents.

•Helps in growing seedless fruits.

(iv)Spore Formation:spores are small bulb like structure which are covered by thick walls.Under favourable conditions, they germinate and produce new organism.

Sexual Reproduction in plants

when reproduction takes place as a result of the fusion of male and female gametes is called sexual reproduction.

Fusion of gametes is called fertilization which results in variation.

Sexual Reproduction in Plants 

→Flower are the reproductive organs of plants.

→A typical flower consists of four main roles namely sepals, petals, stamen and pistol.

Types of flowers

•Bisexual Flower:Both male and female reproductive parts are present.Eg;Hibiscus, mustard.

•Unisexual Flower:Either male or female reproductive parts is present.Eg, papaya, watermelon.

Structure of flower:

Process of seed Formation

•Pollen grains, produced in the another , are transferred to the stigma of same flower (self pollination)or stigma of another flower(cross pollination)through agent like air , water or animals.

•Pollen grains germinate and form pollen tubes which pass through style to reach up to the ovules present in ovary.

•The fusion of male / female gametes is called fertilization.Zygote is produced inside the ovary.

•Zygote divides to form embryo.ovale develops thick coat and changes into seed gradually.

•Ovary changes into fruit and other parts of flower fall off.

•The seed germinates to form a plant under suitable conditions such as air , moisture etc.

Reproduction of Human beings

→Human use sexual mode of reproduction.

→sexual maturation:The period of life when production of germ cells I.e, Ova (female)and sperm(male)start in the body.This period of sexual maturation is called puberty.

Changes of Puberty

(a)common in male and female

•Thick hair growth in armpits are genital area.

•Skin becomes oily, may result in pimples.

(b)In girls

•Breast size begin to increase.

•Girls begin to menstuate.

(c)In boys

•Thick hair grown on face .

•Voice begin to crack.

These changes signals(symtoms) that sexual maturity is taking place.

Male Reproduction system

(a)Testes:A pair of teste are located inside scrotum which is present outside the abdominal cavity.Scrotum has a relatively lower temperature needed for the production of sperm.

•Male germ cell i.e Sperms are formed here.