How do Organisms Reproduce? – Case-based Questions with Answers
Class 10
CBSE Board Examinations
Designed strictly as per NCERT syllabus • Read scenario, answer and check model solution
Designed strictly as per NCERT syllabus • Read scenario, answer and check model solution
Instructions: Read each scenario carefully. Each case contains 1–3 short questions followed by clear, exam-focused answers. Use these for application-based practice and board preparation.
A. Basics & Asexual Reproduction (Case 1–4)
Case 1: A class observes two unicellular organisms—Organism X divides into two similar cells rapidly, while Organism Y forms multiple small cells inside and then releases them.
Q1. Identify the modes of reproduction shown by X and Y.
A1. X shows binary fission (division into two). Y shows multiple fission (many daughter cells formed after repeated nuclear divisions).
Q2. Give one advantage of these modes in unicellular life.
A2. Rapid population increase under favourable conditions, allowing quick colonisation.
Case 2: A gardener reports rapid spread of potato plants in a field where tubers were left in soil.
Q3. Explain how potatoes reproduce and name the vegetative structure involved.
A3. Potatoes reproduce vegetatively via tubers (swollen underground stems) that bear buds ('eyes') which sprout into new plants.
Q4. State one advantage and one disadvantage of this method for farmers.
A4. Advantage: produces uniform crops with desired traits. Disadvantage: diseases can spread easily through infected tubers; low genetic variation.
Case 3: In an aquarium, yeast forms small outgrowths that eventually detach and swim freely.
Q5. Name the asexual method and briefly describe it.
A5. Budding — a new individual forms as a protrusion (bud) on the parent which grows and detaches (seen in yeast and Hydra).
Q6. How does budding ensure survival in stable environments?
A6. Budding allows rapid multiplication without mating; clones well-adapted to current conditions proliferate efficiently.
Case 4: A fungus releases light spores from a black structure during dry weather and new hyphae appear where spores land.
Q7. What structure releases spores? What is their functional advantage?
A7. Sporangium (or conidiophore) releases spores. Spores are small, resistant and produced in large numbers facilitating dispersal and survival in adverse conditions.
B. Vegetative Propagation & Horticulture (Case 5–7)
Case 5: A nursery uses grafting to combine a fruiting variety with a disease-resistant rootstock.
Q8. Briefly explain grafting and why it is useful.
A8. Grafting joins a scion (desired variety) onto a rootstock to combine traits — rapid fruiting, disease resistance, and maintaining cultivar identity.
Q9. Mention one crop where grafting is commonly used.
A9. Apple, grapevine and citrus fruits commonly use grafting.
Case 6: A farmer reports that cuttings taken from healthy plants rooted quickly under mist and formed new plants.
Q10. What is the propagation method? What are two conditions that favour successful cuttings?
A10. Method: Cuttings. Conds: high humidity to reduce transpiration and presence of auxins (or rooting hormone) to promote root formation.
Case 7: A botanical garden grows strawberry runners to expand a bed quickly.
Q11. Explain how runners help propagation and the type of vegetative propagation they represent.
A11. Runners are horizontal stems that produce new plantlets at nodes — natural vegetative propagation (stolon) enabling quick spread without seeds.
C. Sexual Reproduction in Plants (Case 8–12)
Case 8: A student observes a flower under the microscope—stigma is sticky and anther releases heavy, rough pollen grains that stick to bees.
Q12. What type of pollination is suggested and what floral features support it?
A12. Entomophily (insect pollination). Features: sticky stigma, heavy sticky pollen, bright petals and nectar attract insects and aid pollen transfer.
Q13. Why is such adaptation advantageous?
A13. Ensures efficient pollen transfer between flowers of same species, increasing chances of cross-pollination and genetic diversity.
Case 9: In a grass field, pollen grains are lightweight and produced in huge numbers; stigmas appear feathery.
Q14. Identify the pollination mode and reason for these traits.
A14. Anemophily (wind pollination). Light, abundant pollen increases likelihood of contact with feathery stigmas; petals are reduced since pollinators are not needed.
Case 10: A lab shows a pollen tube penetrating the ovule and two sperm nuclei entering — one fuses with the egg and another with polar nuclei.
Q15. Name and briefly explain this process.
A15. Double fertilization — one sperm fertilizes egg (zygote), the other fuses with polar nuclei forming triploid endosperm (nutritive tissue for embryo).
Q16. State its significance for seed formation.
A16. Synchronises formation of embryo and nutritive endosperm ensuring embryo has food for germination, increasing seed viability.
Case 11: After pollination and fertilization, the ovary becomes fleshy and develops into fruit which is eaten by birds; seeds are later found in new areas.
Q17. Which seed dispersal mechanism is illustrated and how does fruit structure help?
A17. Zoochory (animal dispersal). Fleshy fruits attract animals; seeds survive passage through gut or are dropped elsewhere, aiding colonisation of new habitats.
Case 12: A botanist finds a plant that sets seed without visible pollen transfer or pollinators; seeds are genetically identical to the parent.
Q18. Name this phenomenon and give a short explanation.
A18. Apomixis — seed formation without fertilization, producing clonal offspring identical to the mother plant, common in some grasses and citrus varieties.
D. Human Reproduction — Male & Female (Case 13–16)
Case 13: A couple consults a doctor because the male partner's semen analysis shows low motility and count.
Q19. List two possible causes of low sperm motility/count and one standard treatment approach.
A19. Causes: infections, varicocele, hormonal imbalance, heat exposure, lifestyle (smoking). Treatment: lifestyle changes, antibiotics if infection, surgical correction (varicocele), or ART such as ICSI in severe cases.
Case 14: A young woman has irregular periods and difficulty conceiving; tests indicate polycystic ovary syndrome (PCOS).
Q20. Explain PCOS briefly and two management strategies for improving fertility.
A20. PCOS is a hormonal disorder with ovulatory dysfunction and cystic ovaries leading to irregular cycles and infertility. Management: lifestyle modification (weight loss), ovulation induction drugs (clomiphene), and assisted reproductive techniques if needed.
Case 15: During antenatal care, ultrasound shows the placenta positioned normally and the fetus growing; mother receives iron and folic acid supplements.
Q21. State two functions of the placenta and why folic acid is recommended in pregnancy.
A21. Placenta: nutrient and gas exchange between mother and fetus; hormone production (hCG, progesterone) supporting pregnancy. Folic acid prevents neural tube defects and supports rapid cell division in early embryo development.
Case 16: A woman chooses an intrauterine device (IUD) for contraception and returns for follow-up to check placement.
Q22. How does an IUD prevent pregnancy and what are potential side-effects to monitor?
A22. IUDs prevent implantation and may create a local inflammatory environment harmful to sperm and ova; some release copper or levonorgestrel. Side-effects: altered bleeding patterns, cramping, risk of expulsion or infection in rare cases.
E. Gametogenesis, Fertilization & Development (Case 17–20)
Case 17: Microscopic slides show dividing germ cells in testes with successive stages from spermatogonia to spermatozoa.
Q23. Outline key stages of spermatogenesis and the role of testosterone.
A23. Spermatogonia (mitosis) → primary spermatocytes (meiosis I) → secondary spermatocytes (meiosis II) → spermatids → spermatozoa (spermiogenesis). Testosterone (from Leydig cells) supports spermatogenesis and development of male secondary characteristics.
Case 18: A fertilized egg divides to form a blastocyst which implants in uterine lining by day 7.
Q24. Describe early embryonic stages from zygote to implantation.
A24. Zygote undergoes cleavage forming a morula, then a blastocyst (inner cell mass + trophoblast). Blastocyst attaches to and embeds in endometrium (implantation), trophoblast forms placenta while inner cell mass forms embryo.
Case 19: A patient exposed to teratogens in early pregnancy is counselled about risk of congenital defects.
Q25. Define teratogen and give two examples; why is timing of exposure critical?
A25. Teratogen: agent causing developmental abnormalities (e.g., certain drugs like thalidomide, alcohol, some infections like rubella). Timing matters because organogenesis occurs early; exposure during critical windows can cause major malformations.
Case 20: A public health team runs an awareness drive on STIs, safe sex and vaccination for HPV in adolescents.
Q26. List three key messages to include in such a campaign and one reason HPV vaccination is recommended.
A26. Messages: condom use reduces STI risk, importance of regular screening and treatment, seek antenatal care and avoid risky behaviours. HPV vaccine recommended to prevent HPV infection that can cause cervical cancer; best given before sexual debut for maximum efficacy.