Class 10 Science Chapter 7 How do Organisms Reproduce? NCERT Solutions 2026 PDF Download

Ans: DNA (Deoxyribonucleic Acid) contains the blueprint for body design and function. Copying DNA ensures that the offspring receives the same blue-print as the parent, maintaining body design essential for survival. Minor inaccuracies during copying introduce variations, which are useful for the evolution and adaptation of the species.

Ans: Variations allow a species to adapt to drastically changing environments (like global warming or new diseases). If a population were identical, a single change could wipe them all out. Variation ensures that at least some variants survive to continue the species. It is a survival insurance for the species, though it may not help a specific individual survive.

Ans:

• Binary Fission: The parent cell divides into two equal daughter cells. Example: Amoeba, Leishmania.
• Multiple Fission: The parent cell divides into many daughter cells simultaneously inside a cyst. Example: Plasmodium (Malaria parasite).

Ans: 1. It is the only method to grow plants that have lost the capacity to produce viable seeds (e.g., Banana, Rose, Jasmine).
2. It ensures that the offspring are genetically identical to the parent, preserving desirable traits (like sweet fruit).
3. Plants raised this way bear flowers and fruits earlier than those grown from seeds.

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• Pollination: The physical transfer of pollen grains from the anther (male part) to the stigma (female part) of a flower.
• Fertilization: The biological fusion of the male germ cell (from pollen) with the female germ cell (egg) inside the ovary to form a zygote.

Ans: These glands secrete fluids that mix with sperm to form semen. This fluid:
1. Provides nutrition to the sperms.
2. Provides a fluid medium for easier transport and motility of sperms.

Ans: 1. Growth of hair in armpits and genital area.
2. Development and enlargement of breasts.
3. Darkening of the skin of nipples.
4. Onset of the menstrual cycle (Menstruation).
5. Oily skin and appearance of pimples.

Ans: The embryo gets nutrition from the mother's blood with the help of a special disc-shaped tissue called the Placenta. It connects the embryo to the uterus wall. It contains villi on the embryo's side to provide a large surface area for the exchange of Glucose and Oxygen from mother to embryo and waste products from embryo to mother.

Ans: No. Copper-T is an Intra-Uterine Contraceptive Device (IUCD) that prevents pregnancy by preventing implantation. It does not provide a physical barrier against body fluids, so it cannot prevent the transmission of STDs (like Syphilis, HIV-AIDS).

Ans:

• Self-Pollination: Transfer of pollen from anther to stigma of the same flower.
• Cross-Pollination: Transfer of pollen from anther of one flower to stigma of another flower (same or different plant). Requires agents like wind, water, or insects.

Ans: Sperm formation requires a temperature lower than the normal body temperature. The scrotum (which holds the testes) is located outside the abdominal cavity to maintain a temperature about 2-3°C lower than the body, which is ideal for spermatogenesis.

Ans: If fertilization does not occur, the thick and spongy lining of the uterus (prepared to receive the embryo) is not needed. It slowly breaks down and comes out through the vagina as blood and mucus. This cycle takes place roughly every month and is called Menstruation.

Ans: Regeneration is the ability of an organism to grow into a complete individual from its cut body parts. Specialized cells proliferate and differentiate to form various tissues.
Example: Planaria and Hydra.

Ans: Leishmania (which causes Kala-azar) reproduces by Binary Fission. However, unlike Amoeba, the splitting occurs in a definite orientation in relation to the whip-like structure (flagellum) at one end of the cell.

Ans:
Pistil (Female): Stigma (top, sticky), Style (tube), Ovary (base, contains ovules).
Stamen (Male): Anther (top, pollen), Filament (stalk).

Ans: 1. Barrier Methods: Condoms, Diaphragms. Prevent sperm meeting egg. (Protects from STDs).
2. Chemical Methods: Oral pills. Change hormonal balance to prevent egg release.
3. IUCD: Loop or Copper-T placed in uterus to prevent implantation.
4. Surgical Methods: Vasectomy (blocking vas deferens in males) or Tubectomy (blocking fallopian tubes in females).

Ans: Testes (Formation) → Vas Deferens (Transport) → Receives secretions from Seminal Vesicle & Prostate → Urethra (Common passage for urine and sperm) → Penis (Exterior).

Ans: Complex organisms are not just a random collection of cells; they have specialized tissues and organs placed at specific positions. They lack specific "totipotent" cells capable of growing into an entire organism from a cut piece. Hence, they need complex reproductive systems rather than simple regeneration.

Ans: Reproduction ensures that new individuals are produced to replace those that die due to aging, disease, or predation. By maintaining a balance between birth rate and death rate, reproduction ensures the continuity and stability of the population size of a species in its niche.

Ans: It is an asexual reproduction method where the parent plant produces hundreds of microscopic reproductive units called spores inside a spore case (sporangium). When the case bursts, spores spread into the air. Under favourable conditions (moisture), they germinate.
Example: Rhizopus (Bread Mould).

Ans:

• Menarche: The start of menstruation at puberty (around age 11-13).
• Menopause: The permanent stoppage of menstruation in women (around age 45-50), marking the end of reproductive capacity.

Ans: Site: Fallopian Tube (Oviduct).
Product: Zygote (which divides to form an Embryo).

Ans: In simple multicellular organisms, the body breaks up into smaller pieces (fragments) upon maturation. Each fragment grows into a new individual.
Example: Spirogyra.

Ans: 1. Large numbers of spores are produced.
2. Spores are covered by a thick wall that protects them from unfavorable conditions (heat, drought) until they find a moist surface.