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.

NCERT Exercise Solutions

1. Why is reproduction essential for organisms?

• Answer: Reproduction is essential for organisms because it ensures the continuity of species by producing new individuals, allowing genetic information to pass on from one generation to the next.

2. Which is a better mode of reproduction: sexual or asexual? Why?

• Answer: Sexual reproduction is generally considered better because it introduces genetic variation, which increases the chances of survival for the species in changing environments.

3. Why is the DNA copying mechanism important in reproduction?

• Answer: DNA copying is important as it transfers genetic information to the next generation, ensuring the offspring carry the traits of their parents. However, minor variations in DNA are crucial for evolution.

4. How does binary fission differ from multiple fission?

• Answer: In binary fission, a single organism divides into two equal parts (e.g., Amoeba), while in multiple fission, the organism divides into multiple offspring at once (e.g., Plasmodium).

5. How will an organism be benefited if it reproduces through spores?

• Answer: Spores are resistant to adverse conditions, allowing survival in extreme environments. They can be easily dispersed, increasing the chances of reproduction in various locations.

6. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

• Answer: In complex organisms, body systems and specialised cells perform distinct functions, making regeneration difficult beyond minor repair. Regeneration in such organisms cannot produce a complete new individual.

7. Why is variation beneficial to the species but not necessarily for the individual?

• Answer: Variations provide a survival advantage to a species by creating diversity that helps adaptation to environmental changes. However, for an individual, certain variations may be disadvantageous.

8. How does reproduction help in providing stability to populations of species?

• Answer: Reproduction maintains population size by replacing deceased individuals, ensuring species survival, and contributing to genetic stability through inheritance.

9. What could be the reasons for adopting contraceptive methods?

• Answer: Contraceptive methods are adopted to control family size, prevent unintended pregnancies, reduce the spread of STIs, and promote reproductive health.

10. What are sexually transmitted diseases? Name some examples.

• Answer: Sexually transmitted diseases (STDs) are infections spread through sexual contact. Examples include HIV/AIDS, gonorrhoea, and syphilis.

11. How does fertilisation take place in human beings?

• Answer: In humans, fertilisation occurs in the fallopian tube where the sperm meets the ovum (egg) released from the ovary, combining genetic materials to form a zygote.

12. What are the different methods of contraception?

• Answer: Methods of contraception include:
  • Barrier methods (e.g., condoms, diaphragms)
  • Hormonal methods (e.g., pills, injections)
  • Intrauterine devices (IUDs)
  • Surgical methods (e.g., tubectomy, vasectomy)
  • Natural methods (e.g., rhythm method)

13. How does the embryo get nourishment inside the mother’s body?

• Answer: The embryo gets nourishment through the placenta, an organ that attaches the embryo to the uterus, facilitating nutrient and oxygen exchange and waste removal between the mother and the embryo.