Class 10 Science Notes (Class 10)

CBSE Class 10 Science Chapter 8 How do Organisms Reproduce?

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How do Organisms Reproduce?

How do Organisms Reproduce

How do Organisms Reproduce


Reproduction is the process by which living organisms produce new organisms similar to themselves.
Reproduction plays an important role in the following ways:
  • Retain a particular species of living organisms
  • Transmission of characters from one generation to the next
  • Variations lead to the origin of new species
There are 2 modes of reproduction:
  • Asexual reproduction
  • Sexual reproduction

Asexual Reproduction

How do Organisms Reproduce

Asexual Reproduction

  • Mode of reproduction in which new individuals are formed from a single parent
  • No sex involved
  • New individuals are identical to the parent (Clone)
  • Faster mode of reproduction
  • Seen in Amoeba, Hydra, Flatworms, many plants like rose, potato, onion etc.
Various types of asexual reproduction are:
  • Fission
  • Budding
  • Regeneration
  • Fragmentation
  • Spore formation
  • Vegetative propagation


An organism splits to form two/more new individuals
  • Binary fission
  • Multiple fission
Binary fission
  • Two new individuals are formed
  • Nucleus divides only once
  • Unicellular organisms like amoeba, paramecium, euglena, bacteria
Multiple fission
  • Many new individuals are formed
  • Nucleus divides repeatedly
  • Takes place during unfavorable conditions (cyst formation takes place)
  • Amoeba, plasmodium, many algae


  • New individual is formed as an outgrowth of parent
  • Daughter separates away & parent continues to exist
  • Hydra, Yeast


  • Parent breaks into multiple pieces on maturity, each of which gives rise to a new individual
  • Seen in simple multicellular organisms (Spirogyra)


  • Parent if cut/broken into multiple pieces , each gives rise to a new individual
  • This is an accidental process
  • Hydra, flatworm, tapeworm

Spore Formation

Formation of new individual by germination of spores

Spores are unicellular bodies in the parent that are capable of growing into a new individual
  • Conidia
  1. Non-motile spores of fungus (Penicilium)
  2. Termed as Mitospores
  • Zoospores
  1. Motile spores
  2. Uses Flagellum for locomotion
  3. Used as a mode of asexual reproduction by some algae, bacteria & fungi.

Vegetative Propagation

It is the mode of asexual reproduction in plants. Plant parts are detached from the parent & form a new plant. Structures which help in vegetative propagation are called Vegetative propagules. Example: Rhizome, tuber etc.
Natural vegetative propagation
  • Root
  • Stem
  • Leaves
Artificial vegetative propagation
  • Cutting
  • Layering
  • Grafting

Natural Vegetative Propagation

By roots
  • Buds develop in thick, fleshy roots which later, when put into soil develop into new plants
  • Guava, sweet potato, dahlia
By stems
  • Stems that grow horizontally above ground
  • Examples: Grass, strawberry
Underground stems
  • Potato’s tubers which are fleshy are underground storage structures. Buds give rise to aerial shoots under favorable conditions.
  • Ginger’s rhizomes are modified stems found underground. Buds appear at their nodes which can give rise to new plants.
  • Onion’s bulbs are short underground vertical shoots with thickened leaves. Roots emerge from underside of the stem.
By leaves
  • Buds are formed along leaf margins which later give rise to a new plant
  • Examples: Bryophyllum

Artificial Vegetative Propagation

A plant part is cut from the parent & put into the soil which later give rise to a new plant.
  • Stem cutting: Rose, sugarcane
  • Root cutting: Dahlia
  • New plants are formed from stems of parent plant without detaching them initially from the parent. A variety of plants can be grown by this method like strawberry, guava, lemon, china rose etc..
    • Mound layering
A branch is pulled towards ground and then a part of it is covered with moist soil. New roots later develop from this part, after which it gets detached from the parent plant.
  • Air layering
An aerial branch is scraped and covered with moist mud which is then covered with plastic. New roots develop after sometime, after which the new part gets detached from the parent.
Stems cut from two different plants are attached to grow as a single plant. This improves the quality of certain plants.

Sexual Reproduction

  • Mode of reproduction in which new individuals are formed from two parents
  • Sex is involved (Fusion between male & female gametes give rise to the new organism)
  • New individuals are not identical to the parents
  • Variations occur
  • Relatively slower mode of reproduction

Advantages of Sexual Reproduction

  • To incorporate variations in species which in turn ensures survival of a species
  • Each individual in a species has its own uniqueness & identity
  • Enables organisms to survive under unfavorable conditions


  • Gametes are the Sex cells
  • In some organisms, Male & Female gametes are identical to each other (Isogamy) Example: Spirogyra
  • While in some others, Male & Female gametes are different from each other (Anisogamy) Example: Human beings
  1. Male gamete: motile
  2. Female gamete: food storage
  3. Fusion of male & female gametes gives rise to a new organism
  • Sexual Reproduction in Plants

    Flower is the Reproductive organ of a plant
    A flower is said to be :
  • If either male/ female reproductive part is present in it
  • Example: papaya, watermelon

  • Bisexual:
  • If both male & female reproductive parts are present in it
  • Example: china rose, mustard
  • Stalk: Holds the flower
  • Thalamus: Swollen upper portion of stalk
  • Petals: Colored parts of a flower which attracts insects
  • Sepals: Ensures protection
  • Stamen: Male reproductive organ which produce male gametes (pollen grains)
  • Carpel: Female reproductive organ which produce female gametes (ovum/egg)

Male Reproductive Structure in a Flower : Stamen

Stamens are the male reproductive structures in a plant. The structure of a stamen consists of 3 important parts:
  • Filament
  1. Stalk that bears anthers
  • Anther
  1. Bilobed structure at the tip of filament

  2. Each lobe has 2 pollen sacs
  3. A total of 4 pollen sacs are present in a anther
  4. Each sac produces spores, which later develop into pollen grains, the male gametes
  • Connective
  1. Part attached to the back of anther

Female Reproductive Structure in a Flower: Carpel

Carpel has 3 important parts in a flower                
  • Ovary
  1. Basal enclosed part of carpel
  2. Ovarian cavity is termed as Locule
  3. Encloses ovule in it
  4. Ovules are attached to cushion-like structure called Placenta
  • Style
  1. Tube like structure that connects the Ovary & Stigma
  • Stigma
  1. Located at the exposed end of Style
  2. Acts as the receptive surface for pollen grains

Sexual Reproduction in Plants: Steps

 Following steps together complete sexual reproduction in plants:
  1. Pollination
  2. Fertilization
  3. Seed formation
  4. Germination


Transfer of pollen grains from anther to stigma is termed as Pollination. This transfer of pollen grains occurs with the help of pollinating agents like wind, water, insects, birds etc.
There are 2 types of pollination:
  • Self pollination
  1. Transfer of pollen grains from anther to stigma of the same flower
  • Seen in leguminous plants like pea
  • Cross pollination
  1. Transfer of pollen grains from anther of one plant to stigma of the another plant
  2. Seen in large number of plants like onions, broccoli etc.
  • Fertilization

  • Fusion of pollen & egg is called fertilization
  • Fertilization takes place inside the female reproductive part
  • Zygote is formed which later grows into embryo
  • Seed Formation

  • Zygote divides repeatedly to form Embryo
  • Ovule develops a thick coat & forms seed
  • Ovary ripens to form fruit
  • Germination

  • Development of a seedling from a seed
  • Sexual Reproduction in Human Beings

  • Sexual reproduction is the only mode of reproduction
  • Period during which the rate of general body growth slows down & reproductive tissues starts maturing is termed as Puberty/ Adolescence
  • A human male reaches puberty at 13-14 years, whereas a female reaches the same around 11-13 years
  • Following changes are observed during Puberty:
  • Thick hair growth under armpits & genital area
  • Facial hair
  • Change in voice
  • Occasional Penis enlargement
  • Female
  • Start of menstruation cycle
  • Breast enlargement
  • Hair growth under armpits & genital area
  • Human Male Reproductive System

     Human male reproductive system consists of the following parts:
  • Testes
  1. Occur in pairs
  2. Produce sperms
  3. Produce male hormone, testosterone
  • Scrotum
  1. Extension of abdominal cavity containing testes
  2. Protects testes
  3. Maintains a temperature lower than body temperature
  • Epididymis
  1. Complex tube like structure in scrotum
  2. Stores sperms, helps in passage of sperms
  • Vas deferens
  1. Tube like structure emerging from lower part of epididymus
  2. Opens to the ejaculatory duct
  • Penis
  1. Muscular, copulatory organ
  2. Discharge sperms when stimulated
  • Urethra
  1. Tube like structure
  2. Common passage for both sperms & urine
    • Reproductive glands:
  • Prostate gland
  1. Secretes milky fluid that helps in sperms mobility
  • Seminal vesicles
  1. Produce viscous fluid which help in sperm mobility in female
  • Cowper’s gland
  1. Secretes mucous to lubricate female passage

Sperms: The Male Gametes

  • Tiny bodies with long tail
  • Mainly composed of genetic material
  • Sperms are produced in testes. Around 12 billion sperms are produced per month.
  • Sperms move from Testes to Epididymus where they mature
  • Before intercourse, Penis gets filled with blood and becomes erect.
  • Mature sperms move from Epididymus to Vas deferens
  • Ducts of seminal vesicle and prostate gland combine with Vas deferens to form the Ejaculatory duct
  • The liquid mixture (consisting of sperm) from the Ejaculatory duct joins the urethra and gets ejaculated.
  • Of 300 million sperms ejaculated, only 200- 300 survive to reach the egg cell & only one succeed to fertilize it.

Human Female Reproductive System

Female reproductive system consists of the following parts:
  • A pair of Ovaries
  1. One on each side of uterus
  2. Produce female sex cell (ovum/ova)
  3. Secrete female hormones estrogen & progesterone
  • Fallopian tube
  1. Exist in pairs , originating from uterus extending up to each ovary
  2. Receives ovum from ovary
  • Uterus
  1. Pear-shaped muscular hollow structure
  2. Foetus develops here
  • Cervix
  1. Narrow lower part of uterus
  • Vagina
  1. Tube like structure
  2. Sperm discharge occurs here
  3. Acts as birth canal

Ovum: The Female Gamete

  • Ovum is the female sex cell. Also called Egg cell
  • Ova are produced by epithelium in ovary
  • Release of ovum from ovary is termed as Ovulation
  1. Ovary gets matured by puberty
  2. Ova are produced by germinal epithelium of ovary
  3. Formation of ova starts in foetus even before birth. At birth, there are 2-3 lakhs immature eggs. After attaining puberty, these immature eggs start getting matured under the influence of hormones from pituitary gland.
  4. One matured ovum is released from either ovary at every 28 days. This process of release is Ovulation

Fertilization in Human Beings

Fertilization is internal in human beings
  • This process occurs in the fallopian tube
  • Ovum comes from ovary to Fallopian tube. Unfertilized egg remains alive for approx. 24 hours
  • Sperms enter through vagina and reach the Fallopian tube. Sperm must fertilize the egg within the above time.
  • Sperm enters the egg
  • Fusion of nucleus of sperm & ovum is termed as Fertilization
  • Fertilization leads to the formation of single-celled Zygote
  • Zygote undergoes repeated divisions, and gets implanted in the uterus. This is now called as Embryo. Embryo in advanced stages of development is termed as Foetus.
  • Uterus also prepares itself to receive the embryo. It thickens its walls. Embryo descends into uterus in 4-5 days from the day of fertilization.
  • Embryo in the uterus receives nutrients from the mother’s body through the Umbilical cord which in turn is connected to the uterine wall of mother through Placenta. Placenta: is a structure formed by specialized tissues of fetus & uterine wall of mother.
  • Nutrients enter through this cord, and wastes go out of the foetus body. Umbilical cord also has arteries & veins for exchange of oxygenated and deoxygenated blood.

Sexual Cycle in Females: Menstruation

  • An egg is released from either of the ovaries every 28 days. The unfertilized egg is alive for 24 hours after ovulation. Uterus prepares itself to receive the foetus. As a result, the Endometrium thickens.
  • If fertilization doesn’t take place, then no zygote is formed. Therefore, endometrium breaks which results in bleeding through vagina.
  • Process of bleeding though vagina due to breakage of endometrium is termed as ‘Menstruation’. This bleeding lasts for 2-6 days. This occurs approx. 14 days after ovulation.
  • Since Menstruation occurs every 28 days; this is also referred as Menstrual cycle
  • Menstrual cycle in a woman continues till 45-55 years of age, post which ovary becomes dormant. No ovulation, no menstruation occurs after this. This is termed as “Menopause”

Reproductive Health

Reproductive Health is a state of complete physical, mental and social well-being in all aspects of reproduction. People should have adequate knowledge on the following:
  • Knowledge of reproductive processes & organs
  • Care of mother & child
Following points to be remembered to ensure good care of the mother & the child:
  1. Proper nutritious diet to pregnant woman as well as lactating mothers
  2. Proper age difference between children
  3. Planning a baby at the right age of mother (between 20-35 years)
  4. Restrict the number of children not to add to overpopulation
  5. Avoid unwanted pregnancy
  • Family planning
Family planning is necessary to limit this huge increase in population.
Overpopulation can give rise to serious problems like lack of food, employment and education which in turn would affect the economy and also the survival of population.
  • Knowledge on STDs (Sexually Transmitted Diseases)

Family Planning

Some people give birth to a child every year; others end up with 10- 11 children. It is very important to understand the disadvantages of overpopulation and proactively act to control the same. Following points can ensure that the population does not increase beyond limit:
  • Control the number of children in a family to one/two depending upon the family’s income
  • No differentiation between male & female child. Some people end up giving birth to 6-7 daughters just to get a son.
  • Proper age gap between children must be maintained, so that enough care is provided to the first child even before the second one arrives.
  • Parents should plan a baby at their right age. If parents are too old in the 40s , they themselves become too old to take care of kids. Similarly parents as young as 19- 20 years old couples are too young to manage kids.
There are several means to avoid unwanted pregnancy or maintain proper gap between children. Some of the ways are as follows:
  • Condoms
  1. Balloon like elastic covering that tightly fits over the penis
  2. Collects ejaculated sperms during intercourse
  • Oral contraceptive pills
  1. Does not allow ovulation to occur
  • Surgical method
  1. Vasectomy: Removal of a small portion of Vas deferens
  2. Tubectomy: Removal of a small portion of fallopian tube

Sexually Transmitted Diseases (STDs)

There exists many communicable diseases which spread by sexual contact during intercourse.

Some of these STDs are:

  • Gonorrhea
  • Syphilis
  1. Caused by bacteria and can be treated with antibiotics
  1. Caused by the HIV virus which destroys the immune system of the body. There is no cure for AIDS till date. The person suffering from AIDS eventually dies due to infection.
  • Genital & anal warts
To prevent STDs, ensure the following:
  1. Use of condoms during intercourse
  2. Wash before & after intercourse
  3. Confirm that a new partner is HIV tested before intercourse


SCIENCE Revision Notes

Chapter:01  Chemical Reaction & Equation
Chapter:02  Acid Base & Salt
Chapter:03  Metals & Non Metals
Chapter:04  Carbon & its Components
Chapter:05  Periodic Classification of Elements
Chapter:06  Life Processes
Chapter:07  Control & Coordinates
Chapter:08  How do Organisms Reproduce
Chapter:09  Heridity & Evolution
Chapter:10  Light Reflection Refraction
Chapter:11  The Human Eye & the Colourful World
Chapter:12  Electricity
Chapter:13  Magnetic Effect of Electric Current
Chapter:14  Source Of Energy
Chapter:15  Our Environment
Chapter:16  Management of Natural Resource

Maths Revision Notes

English Revision Notes

Economics Revision Notes

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