Class 10 Science Chapter 8 Revision Notes How do Organisms Reproduce

Class 10 Science Chapter 8 Revision Notes How do Organisms Reproduce, (Science) exams are Students are taught thru NCERT books in some of the state board and CBSE Schools. As the chapter involves an end, there is an exercise provided to assist students to prepare for evaluation. Students need to clear up those exercises very well because the questions inside the very last asked from those.

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Class 10 Science Chapter 8 Revision Notes How do Organisms Reproduce

Asexual Reproduction and Vegetative Propagation

Introduction

Reproduction is the process by which living organisms produce new individuals similar to themselves.
- It ensures continuity of life on earth.
Nucleus of the cell contains DNA (Deoxyribonucleic acid), which is the hereditary material.
DNA replicates and forms new cells causing variation. So, these new cells will be similar but may not be identical to original cell.
Variations are useful for the survival of the individual and species over time. It is the base of 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.
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.

Asexual reproduction takes place through fission, fragmentation, regeneration, budding, vegetative propagation, and spore formation. These modes of reproduction depend on the body design of the organisms.

a) Fission: It is of two types – binary fission and multiple fission.

Binary fission: It is the division of one cell into two similar or identical cells.
- The nucleus first divides amitotically into two, followed by the division of the cytoplasm.
- The cell finally splits into two daughter cells, eg, Amoeba
Multiple fission: In multiple fission, many individuals are formed from a single individual, eg., Plasmodium.
- The nucleus divides repeatedly, producing many nuclei and many daughter cells are formed.

b) Fragmentation: It takes place in multicellular organisms with simple body organisation such as in Spirogyra.

In this, the body breaks up into two or more small pieces of fragments upon maturation.
These fragments grow into new individuals.

c) Regeneration: It is the ability of a fully differentiated organism to give rise to new individual organisms from its body parts.

Small cut or broken parts of the organism’s body grow or regenerate into separate individuals.

For example: Planaria and Hydra.

d) Budding: In budding, a small part of the body of the parent grows out as a bud which then detaches and becomes a new organism.

Hydra reproduces by budding using the regenerative cells.

e) Vegetative Propagation: In many plants, new plants develop from vegetative parts of plant body such as stem, roots, leaves, etc.

Methods of vegetative propagation:

1. Natural methods are:

By roots: eg, Dahlia, sweet potato.
By stems: eg., Potato, ginger.
By leaves: e.g, Bryophyllum (leaf margins bear buds which develop into plants).

2. Artificial methods:

Grafting: e.g., Mango
Cutting: e.g., Rose
Layering: eg, Jasmine
Tissue culture: eg, Ornamental plants, orchid.

f) Spore Formation: Spores are small bulb like structures which are covered by thick walls, under conditions, they germinate and produce new organisms.

Sexual Reproduction in Plants

Parts of Flower

Flowers are main reproductive part of a plant. The main parts of a flower are sepals, petals, stamens and carpels.
Stamens and carpels are the reproductive parts of a flower which contain the germ cells. The male organ of a flower called ‘stamen’ makes the male gamete which are present in the pollen grain. The female organ of a flower called ‘carpel’ makes the female gamete, which are present in ovules of the plant.
Flowers may be unisexual (eg. papaya and watermelon) or bisexual (e.g., Hibiscus and mustard).
Pollination: It is the transfer of pollen grain from the anther of a stamen to the stigma of a carpel.
- Pollination is of two types: self pollination and cross pollination.
The transfer of pollens takes place by agent like wind, water or animals.
After pollination, a pollen tube grows out of pollen grains, through which male germ cell reaches the ovary and fuses with the female germ cell.
Fertilisation is the process of fusion of male and female gamete to produce zygote. It occurs inside the ovary
After fertilisation, ovary develops into fruit whereas ovules into the seed.
Double fertilisation: It is a characteristic feature of flowering plants.
- In this process, out of the two sperm nuclei, one sperm nucleus fuses with the egg nucleus to form an embryo (process is called syngamy) and another fuses with the secondary nucleus to form an endosperm (process is called triple fusion).
Because two kinds of fusion syngamy and triple fusion take place, the process is known as double fertilisation.

Reproduction in Human Beings

Humans have sexual mode of reproduction.
It needs sexual maturation, which is the period of life when production of germ cells i.e, ova (female) and sperm (male) start in the body. This period of sexual maturity is called puberty.

Changes at Puberty are:

a) Common in male and female

Thick hair growth in armpits and genital area.
Skin becomes oily, may result in pimples.

b) In girls:

Breast size begins to increase.
Girls begin to menstruate.

c) In boys:

Thick hair grows on face.
Voice begins to crack.
These changes signal that sexual maturity is taking place.

Male Reproductive System

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

Functions of testes:

Produce male germ cells ie., sperms are formed here.
Testes release male sex hormone (testosterone). Its function is to
Regulate production of sperms.
Bring changes at puberty

b) Vas deferen: It passes sperms from testes towards the urethra

c) Urethra: It is a common passage for both sperms and urine.

Its outer covering is called penis.
It is like a fibromuscular long tube which travels through penis.

d) Associated glands: Seminal vesicles and prostate gland add their secretion to the sperms.

This fluid provide nourishment to sperms and make their transport easy.
Sperm along with secretion of glands form semen.

Female Reproductive System

(a) Ovary: A pair of ovary is located in both sides of abdomen.

Female germ cells i.e., eggs are produced here.
At the time of birth of a girl, thousands of immature eggs are present in the ovary.
At the onset of puberty, some of these eggs start maturing.

(b) Oviduct or Fallopian tube

Receives the egg produced by the ovary and transfer it to the uterus.
Fertilisation i.e, fusion of gametes takes place here.

(c) Uterus: It is a bag-like structure where development of the foetus takes place.

- Uterus opens into vagina through cervix.
- The embryo moves down to reach the uterus. The embedding of the embryo in the thick inner lining of the uterus is called implantation.
The time period from the development of foetus inside the uterus till birth is called gestation period. The act of giving birth to the fully developed foetus at the end of gestation period is termed as parturition.
The breakdown and removal of the inner, thick and soft lining of the uterus along with its blood vessels in the form of vaginal bleeding is called menstrual flow or menstruation.
Reproductive health is all those aspects of general health which help a person to lead a normal, safe and satisfying reproductive life.
Sexually Transmitted Diseases (STDS) are the diseases which spread by sexual contact from an infected person to a healthy person. Some common STDS are Gonorrhoea, syphilis, trichomoniasis, AIDS.
There are different methods which are developed to prevent and control pregnancy such as mechanical methods, chemical methods, oral pills and surgical methods,
Contraception: It is the avoidance of pregnancy, which can be achieved by preventing the fertilisation of ova.

Methods of contraception

(a) Physical barrier

To prevent union of egg and sperm.
Use of condoms, cervical caps and diaphragm.

(b) Chemical methods

Use of oral pills.
These change hormonal balance of body so that eggs are not released.
May have side effects.

(c) Intrauterine contraceptive device (IUDS)

Copper-T or loop is placed in uterus to prevent pregnancy.

(d) Surgical methods

In males the vas deferens is blocked to prevent sperm transfer called vasectomy.
In females, the fallopian tube is blocked to prevent egg transfer called tubectomy.