How do Organisms Reproduce? SSLC 10 Science Notes

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  • Reproduction : Process of giving birth to new organisms.
  • Species : largest group of organisms in which two individuals can produce new organism.
  • Variation : Improper DNA copying leads to variation in new organism, where organisms are similar to their parents but not identical.
  • Asexual mode of reproduction : [Refer the video to understand in detail]
    • Fission : Division of cell in two or more parts. Unicellular organism reproduce by  fission.
      1. Binary fission : Organism split into two equal halves during cell division to form new organism.  E.g. Amoeba.
      2. Multiple fission : Split into many daughter cells during cell division.  E.g.  Plasmodium.
    • Fragmentation : Organisms splits into fragment and each fragment grows into new individual. E.g Spirogyra.
    • Regeneration : Ability of an organism to grow into separate individual from the pieces of  their body parts. E.g.  Planaria.
    • Budding : Bud from the parent body detaches to form a new organism.  E.g.  Hydra.
    • Vegetative Propagation : Parts of plants develops into new genetically similar plants. E.g. Leaf of bryophyllum. This method is used in agriculture for layering and grafting of sugarcane, roses or grapes.
    • Spore formation : Organisms like rhizopus developes into blob-on-stick  structure called sporangia. These sporangia contains spores which  have ability to grow into new individual.
  • Sexual reproduction in flowering plants / Angiosperms :
    • Reproductive organs in flower are stamen and carpel.
    • [Image Reference : Link]
      1. Stamen : Male reproductive part produces pollen grain. Pollen grain  bears male gamete.
      2. Carpel : Female reproductive part which contains stigma, style and ovary.
      3. Stigma : Sticky terminal part.
      4. Style : Middle elongated part.
      5. Ovary : Swollen bottom part containing ovules which contains germ cells/ egg cells.
    • Flowers types based on sex organs:
      1. Unisexual : Posses only one type of sex organ.  E.g. Flowers of Papaya, Watermelon.
      2. Bisexual : Posses both the sex organs. E.g.  Flowers of Hibiscus, mustard.
    • Seed formation : [Refer the video to understand in detail] Pollen grains reaches to stigma in number of ways. It is transferred from stigma to ovary through pollen tube. After reaching overy both male and female gamete fuse to form zygote called fertilization.  Zygote in ovules divides several times to form embryo. Ovule turns into seed while ovary grows into fruit.  Under appropriate condition  embryo inside the seed grows into seedling  called seed germination  which gives rise to new plant.
    • Self Pollination : Transfer of pollen grain takes place in same flower.
    • Cross Pollination : Transfer of pollen grain takes place from one flower to another.
  • Difference between asexual and sexual reproduction:
Asexual Reproduction Sexual Reproduction
One parent needed in asexual reproduction. Two parents needed in sexual reproduction
No formation and fusion of gametes Involves formation and fusion of gametes
Reproduced organisms are genetically similar to parents. Reproduced organism are genetically different from parents.
Is a Fast process Is a Slow process
E.g Reproduction in Hydra, Bryophyllum, etc. E.g. Reproduction in human being, animals, flowering plants etc.
  • Reproduction in Human beings:
    • Common signs of maturity in both males and females:   Faster body growth, thinner hairs on arms and legs, darkening of skin, pimple and oily skin,  Increased Consciousness about body, attraction towards opposite sex.
    • Signs of maturity in males: Voice begins to crack, thick hair growth on face, in armpits and at genital area. Penis starts to become enlarged. It occasionally become erect.
    • Signs of maturity in females: Breast size begins to increase, menstruation starts at this stage.
    • Male Reproductive System: [Refer the video to understand in detail] Male reproductive system consists of testes, vas deferens, penis, scrotum, urethra and various glands like prostate gland, seminal vesicle.
      1. Testes: Testes are located outside body in the scrotum, where male germ cells i.e sperms are produced. Secretes hormone testosterone  which brings changes in appearance during puberty.
      2. Vas deferens: Sperms are delivered through vas deferens. It unite with urethra.  Vas deferens receives secretion from prostate gland and seminal vesicle, which provides transport and nourishment to sperms.
      3. Sperm Cell: Consist of genetic material and a long tail which help them to move towards female germ-cell.
    • Female Reproductive system: [Refer the video to understand in detail] Female reproductive system consist of pair of ovaries, pair of oviducts fallopian tube, uterus, cervix and vagina.
      1. Ovaries: Female germ cells called eggs are produced in  ovaries. Ovaries contains thousands of egg cells which starts to mature at time of puberty.  One ovary produces one egg every month.
      2. Fallopian tube: Open into uterus. While uterus opens into vagina through cervix. Eggs from ovaries are carried from ovaries to womb through fallopian tube. Sperms enter through vaginal passage and reach fallopian tube, where fertilization takes place, forming zygote.
      3. Zygote develops into embryo. Embryo receives nutrition through mother’s blood with help of placenta. Child lives in mothers womb  for nine months and is born  by rhythmic contraction of muscles in uterus.
    • Menstruation: [Refer the video to understand in detail] Uterus prepares itself for receiving fertilised egg by making its lining thick and spongy. It is required to nourishing embryo if fertilization occurs. In absence of fertilization, lining breaks and egg along with blood and mucus comes out of body.
    • Process of releasing blood and other material from the lining of uterus to outside the female body is called menstruation. This takes place every month and so called menstruation cycle.
  • Reproductive Health :
    • Contraceptive Methods : Methods avoids fusion of male and female gametes.
    • Some reasons for adopting contraceptive methods :
      1. Mental readiness for taking responsibility.
      2. Family pressure.
      3. Government rules.
      4. To avoid sexually transmitted disease. E.g. AIDS.
      5. To avoid pregnancy, incase if women is not ready mentally, pregnancy will affect her health.
    • Various contraceptive methods :
      1. Mechanical Barriers : Use of condoms in males and similar covering in females avoids entry of male gametes in female body and also prevents sexually transmitted diseases.
      2. Changing hormonal balance : Use of oral pills changes the hormonal balance due to which eggs are not released and no fertilization takes place. Use of these pills causes side effects on body.
      3. Copper T : Prevents release of eggs and thereby preventing fertilization. It causes irritation in the uterus.
      4. Surgical methods : In female, fallopian tube is blocked, hence, eggs are not released. In males, vas deferens is blocked, hence, sperms are not released.  It can cause infections in the body.
      5. Abortion : Act of removing fetus from the body. An illegal act which is mainly misused to abort girl child.   
    • Population Consideration : Increase in population causes decrease in standard of living and inequality in society.

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