Class 10 Science Notes
~6 min readReproduction keeps a species alive and creates the variation that lets life adapt. Asexual methods such as fission, budding and spores need only one parent, while sexual reproduction in flowering plants and humans depends on the fusion of two gametes. This chapter also covers family planning, safe sex and HIV/AIDS prevention, all of which carry marks every year.
Asexual reproduction needs only one parent and involves no fusion of gametes, so the offspring are near exact copies of the parent with almost no variation. Sexual reproduction needs two parents and involves the fusion of a male and a female gamete, so the offspring inherit a mixture of traits and vary widely. Sexual reproduction is therefore slower but produces far greater variation.
Reproduction is the process by which organisms produce young ones like themselves. Without it, a species would disappear after its last individual died.Reproduction also creates variation. In any population the individuals differ in their traits, and that variation helps a species survive when the environment changes.
Reproduction is not growth
Asexual reproduction needs only one parent and involves no fusion of gametes, so there is almost no variation among the offspring. In many organisms a single cell is enough to give rise to a complete new individual.The common modes are fission, budding, fragmentation, regeneration and spore formation, and each one is linked to a particular organism named in the syllabus.
Match the method to the organism
Many plants reproduce asexually from vegetative parts such as roots, stems and leaves. The new plants are genetically identical to the parent, so a crop stays uniform in yield and quality.Tissue culture and grafting use the same idea deliberately, in laboratories and orchards, to raise large numbers of a variety that could not be grown conveniently from seed.
Name the modified part, not the example
Sexual reproduction needs two parents. Each parent produces gametes, which are haploid cells carrying half the chromosome set, and the fusion of two gametes is called fertilisation.The single cell formed at fertilisation is the zygote. It has the full chromosome number and carries a mixture of traits from both parents, which is the true source of variation.
Why variation matters
The flower is the reproductive organ of a plant. The male part is the stamen, made of the anther and the filament, and the female part is the pistil or carpel, made of the stigma, style and ovary.Pollination transfers pollen from the anther to the stigma. After pollination a pollen tube grows down the style to the ovule, where fertilisation takes place and the zygote begins to develop.
Do not mix up the parts
Humans reproduce sexually. The male reproductive system produces sperms in the testes, and the female reproductive system produces ova in the ovaries. Only one sperm fuses with one ovum.Fertilisation takes place in the oviduct, and the embryo gets implanted in the uterine wall, where it develops for about nine months before birth. Menstruation and pregnancy are both controlled by hormones.
Name the site of fertilisation correctly
Reproductive health means the physical, emotional and social well-being of the reproductive system. It includes knowledge of the body, safe sex, and the ability to have children at the right time with proper medical care.Family planning uses contraception to space out births and to keep the mother and the child healthy. The methods range from simple barriers to long-acting devices fitted by a doctor.
The right to choose
HIV is the human immunodeficiency virus and it attacks the body's immune system, weakening it over time. AIDS is the advanced stage of HIV infection, when the body can no longer fight ordinary infections.HIV is transmitted only by sexual contact with an infected person, transfusion of infected blood, and from an infected mother to her child. It is not spread by shaking hands, sharing utensils, coughing or mosquito bites.
Habits and rights that the board rewards
Quick Revision
Memorise these equations — direct application numericals and derivations in CBSE & JEE frequently hinge on these.
Binary fission
The parent cell divides into two equal daughter cells.
Budding
The bud grows on the parent, matures and then detaches.
Fertilisation
Fusion of gametes restores the full chromosome number.
Pollination to fertilisation
The path taken by pollen from the male to the female part.
Seed and fruit
Which part of the flower develops into what after fertilisation.
Source of variation
Why sexual reproduction produces unlike offspring.
Exam Strategy
High-yield question patterns observed across CBSE boards, JEE Main & Advanced, and NEET.
FAQ
Asexual reproduction uses a single parent and involves no fusion of gametes, so the offspring are almost identical to the parent and to one another. Sexual reproduction needs two parents and involves the fusion of a male and a female gamete to form a zygote. Because two sets of traits are mixed, sexually produced offspring show much greater variation, which is why this form is more valuable to a species in the long run.
Asexual reproduction is faster and needs only one parent, so organisms use it when conditions are favourable and speed matters. Its weakness is that every offspring is genetically alike, so one change in climate or one disease can wipe out the whole population. Sexual reproduction produces variation, and that variation lets some individuals survive a sudden change. In the long run, variation matters more than speed.
Fertilisation takes place in the oviduct, or fallopian tube, where a sperm fuses with the ovum. The sperm travels from the testis through the epididymis, vas deferens and urethra before entering the vagina of the female. After fertilisation the zygote moves to the uterus and implants in the uterine wall. The uterus is therefore the site of implantation, not of fertilisation.
In tissue culture a small piece of plant tissue, called an explant, is placed in a sterile nutrient medium where it divides and grows into a whole plant. It is used to produce large numbers of identical plants quickly. In grafting a shoot of the desired variety is cut and joined to the root system of another plant, so the two tissues grow together. Grafting combines the good fruit of one plant with the strong roots of another.
No. HIV is present mainly in blood, semen, vaginal fluids and breast milk, and it is transmitted only through certain routes. These are unprotected sexual contact, transfusion of infected blood, sharing infected needles, and passage from an infected mother to the child. HIV cannot pass through intact skin, so ordinary contact such as shaking hands, hugging, sharing utensils or sitting together is completely safe.
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