CBSE Class 10 Science Practice Paper 3

Section A: Multiple Choice Questions (MCQs)

1. C) Burning wood - Burning involves a chemical change as it produces new substances (carbon dioxide, water vapor, ash).
2. B) Thyroxine - Thyroxine regulates metabolism by controlling how quickly the body uses energy and makes proteins.
3. B) Volt - The SI unit of electric potential difference (voltage) is the volt (V).
4. C) Roots - Roots show positive geotropism, growing towards gravity.
5. C) Neutralization - The reaction between an acid and a base forms salt and water, neutralizing the pH.
6. D) Digestion of food - The skeletal system does not digest food; this is the role of the digestive system.
7. B) Refraction - Light bends towards the normal when entering a denser medium from a rarer one, which is refraction.
8. C) Accumulation of toxins in food chains - Biomagnification refers to the increase in concentration of a substance, like toxins, in the tissues of organisms at successively higher levels in a food chain.
9. C) Nitrogen - Nitrogen does not significantly contribute to the greenhouse effect; CO₂, CH₄, and H₂O vapor do.
10. B) Ribosome - Ribosomes are the sites of protein synthesis in cells.
11. C) Coal - Coal is a primary energy source in India due to its abundance and established infrastructure.
12. B) Anaerobic respiration - In muscles, under oxygen-deprived conditions, glucose is converted to lactic acid.
13. B) Emulsifying fats - Bile breaks down large fat globules into smaller ones, increasing the surface area for lipase action.
14. D) Spleen - The spleen is part of the lymphatic system, not the respiratory system.
15. C) Both length and cross-sectional area - Resistance (R) is given by R = ρL/A, where ρ is resistivity, L is length, and A is the cross-sectional area.
16. B) Petroleum - Petroleum is a non-renewable resource.
17. B) Decomposition - A reaction where one compound breaks down into two or more simpler substances.
18. D) Both A and C - Xylem transports water and minerals from roots to leaves and provides mechanical support.
19. C) Gonorrhea - Gonorrhea is a sexually transmitted bacterial infection.
20. C) Hydrotropism - The growth movement of roots towards water is hydrotropism.

Section B: Short Answer Questions

21. Diamond vs. Glass Sparkle:

• Diamond has a higher refractive index than glass, leading to greater total internal reflection. This causes light to bounce multiple times within the diamond, creating more sparkles.

22. Pancreas and Blood Sugar:

• The pancreas secretes insulin to lower blood sugar by promoting glucose uptake by cells and glucagon to raise it by converting glycogen to glucose, thus maintaining blood sugar balance.

23. Greenhouse Effect:

• The greenhouse effect naturally warms Earth by trapping heat. Human activities like burning fossil fuels increase greenhouse gases (CO₂, CH₄), enhancing this effect, leading to global warming.

24. Eye Adjustment:

• The eye adjusts focus through the ciliary muscles which change the lens's shape; it becomes thinner for distant vision and thicker for near vision, allowing clear images on the retina.

25. Displacement Reaction:

• Definition: A more reactive metal displaces a less reactive metal from its compound. Example: Zn + CuSO₄ → ZnSO₄ + Cu, where zinc displaces copper.

26. Biodiversity Significance:

• Biodiversity maintains the balance of ecosystems, supports various ecological processes, provides resilience against environmental changes, and is crucial for human resources.

27. Neuron Structure:

• Neurons have dendrites to receive signals, a long axon for transmitting signals over distance, and myelin sheath for faster impulse conduction. Neurotransmitters at synapses ensure accurate signal transmission.

28. Fuse Function:

• A fuse contains a metal strip that melts when current exceeds a safe level, breaking the circuit to prevent damage from excessive current or short circuits.

29. Pollination Process:

• Pollination involves the transfer of pollen from anther to stigma, often by wind, water, or pollinators like bees. The pollen must then grow a pollen tube to reach the ovule for fertilization.

30. Chemical Equation:

• CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O, a decomposition reaction involving acid.

31. Metals vs. Non-Metals:

• Metals: Lustrous, malleable, ductile, good conductors of heat and electricity, high melting/boiling points.
• Non-metals: Dull, brittle, poor conductors, lower melting/boiling points, often gases at room temperature.

32. Deforestation Impact:

• Leads to loss of habitats, increased carbon dioxide levels, soil erosion, disruption of water cycles, and loss of biodiversity, contributing to climate change.

Section C: Long Answer Questions

33. Human Heart:

• a. [Include a labeled diagram showing atria, ventricles, valves, and major blood vessels]
• b. The heart ensures one-way flow via valves:
  • Atrioventricular valves (tricuspid, mitral) prevent backflow from ventricles to atria.
  • Semilunar valves (aortic, pulmonary) prevent backflow from arteries into ventricles.

34. Isotopes:

• a. Isotopes are atoms of the same element with different numbers of neutrons. Example: Carbon-12 and Carbon-14, both have 6 protons but differ in neutron number.
• b. Isotopes of an element have the same atomic number but different mass numbers due to differing neutron counts. They have similar chemical properties but may differ in physical properties like stability.

35. Electric Generator:

• a. [Diagram showing coil rotation in a magnetic field, slip rings, brushes, and output]
  • An electric generator converts mechanical energy into electrical energy through electromagnetic induction.
• b. Advantages of AC over DC include:
  • Easier to generate and transmit over long distances with less energy loss due to transformers.
  • Can be easily stepped up or down in voltage.

36. Plant Reproduction:

• a. Asexual methods include:
  • Vegetative propagation: Using plant parts like stems (e.g., rose cuttings).
  • Fragmentation: Breaking into parts that grow into new plants.
  • Spore formation: Spores grow into new plants under favorable conditions.
• b.Sexual: Leads to genetic diversity, better adaptation to changing environments, but requires energy for mating.
  • Asexual: Quick reproduction, no need for a mate, maintains desirable traits, but less genetic variability.

37. Nitrogen Cycle:

• a. [Labeled diagram showing nitrogen fixation, nitrification, assimilation, ammonification, denitrification]
  • Nitrogen cycle involves conversion of nitrogen gas into forms usable by plants and back to N₂.
• b. Human activities like fertilizer use, combustion, and deforestation disrupt the cycle by adding excess nitrogen compounds, leading to environmental issues like eutrophication.

38. Human Respiration:

• a. Respiration involves inhaling oxygen, which diffuses into the blood through alveoli. CO₂ is exhaled. Alveoli provide a large surface area, thin walls, and moist environment for efficient gas exchange.
• b.Breathing: Physical process of air movement in and out of lungs.
  • Cellular Respiration: Biochemical process in cells converting glucose into ATP, CO₂, and H₂O.

39. Plastic Pollution:

• a. Consequences include harm to wildlife, marine life ingestion leading to death, microplastics in the food chain, and pollution of land and water bodies.
• b. Measures to reduce include:
  • Encouraging recycling and proper waste management.
  • Promoting biodegradable and compostable materials.
  • Reducing single-use plastics through legislation and consumer education.