CBSE Class 10 Science Practice Paper 2

Section A: Multiple Choice Questions (MCQs)

1. B) Silicon - Silicon is a metalloid, having properties of both metals and non-metals.
2. A) Transpiration - Transpiration is the process where plants lose water vapor through their leaves.
3. A) 1.2 Ω - For parallel resistors, 1/R = 1/R₁ + 1/R₂ = 1/2 + 1/3 = 5/6. Therefore, R = 6/5 Ω = 1.2 Ω.
4. D) All of the above - All mentioned are secondary sexual characteristics in males.
5. C) Carbon dioxide - CO₂ is produced during digestion, especially when carbohydrates are broken down.
6. A) Erosion - Erosion is the process where soil particles are carried away by wind or water.
7. B) Spleen - The spleen, while part of the lymphatic system, is not part of the digestive system.
8. B) Concave - A concave lens diverges light rays.
9. C) Diffraction - Diffraction is the bending of light around the edges of an obstacle.
10. B) Convex - Convex mirrors are used as rear-view mirrors because they provide a wider field of view.
11. C) Catalyst - A catalyst increases the rate of a reaction without being consumed.
12. A) Chromosomes of the father - The sex of a child is determined by whether the sperm carries an X or Y chromosome.
13. C) Light to electrical - Solar cells convert sunlight directly into electrical energy.
14. C) Increased oxygen levels - Deforestation leads to decreased oxygen levels due to fewer trees for photosynthesis.
15. A) Increases by 10 times - Each decrease of one pH unit means the H⁺ concentration increases tenfold.
16. B) Adrenaline - Adrenaline is released during stress, initiating the fight or flight response.
17. C) Producers - Producers (plants) have the highest energy content as they convert solar energy into chemical energy.
18. A) Nitrogen fixation - Nitrogen fixation converts atmospheric nitrogen into nitrates usable by plants.
19. D) High pollution emission - A good fuel should have low pollution emissions.
20. C) Phototropism - Bending towards light is phototropism.

Section B: Short Answer Questions

21. Maintaining Internal Environment:

• The kidneys regulate body fluid volume, electrolyte concentration, and pH by filtering blood, reabsorbing necessary substances, and excreting waste as urine. They also control blood pressure via renin and manage red blood cell production through erythropoietin.

22. Electrolysis of Water:

• 
• Electrolysis of water uses an electric current to split water into hydrogen and oxygen gases: 2H₂O → 2H₂ + O₂. Anode produces O₂, cathode H₂.

23. Alloys:

• An alloy is a mixture of metals or a metal with another element. Examples:
  • Brass: Copper and zinc, used for its corrosion resistance.
  • Steel: Iron with carbon, for strength. Alloys are used for enhanced properties like durability, resistance to corrosion, or better conductivity.

24. Cerebellum's Role:

• The cerebellum coordinates voluntary movements, maintains posture, and balance. It receives information from sensory systems, the spinal cord, and other parts of the brain to fine-tune motor activities.

25. Neuron Structure and Function:

• Neurons have a cell body, dendrites for receiving signals, and a long axon for sending signals. The myelin sheath speeds up impulse transmission, and neurotransmitters facilitate communication at synapses.

26. Power in Electric Circuits:

• Power (P) is the rate at which electric energy is consumed or produced. Formula: P = VI = I²R = V²/R, where V is voltage, I is current, and R is resistance.

27. Bent Pencil in Water:

• Due to refraction, light bends as it moves from air to water, making the pencil appear bent at the water's surface because the light path changes.

28. Law of Dominance:

• Mendel's law states that one allele (dominant) masks the effect of another (recessive) in heterozygous individuals. Example: In pea plants, the tall allele (T) is dominant over the dwarf allele (t). A plant with Tt genes will be tall.

29. Bacteria and Fungi in Nutrient Cycles:

• Bacteria and fungi decompose organic matter, releasing nutrients back into the soil. They fix nitrogen, making it available for plants, and degrade pollutants, contributing to soil health.

30. Magnesium and Oxygen Reaction:

• 2Mg + O₂ → 2MgO. This is an oxidation-reduction reaction, specifically a synthesis reaction.

31. Greenhouse Effect and Global Warming:

• Greenhouse gases like CO₂ trap heat, warming the Earth. Increased emissions amplify this effect, leading to climate change by enhancing the natural greenhouse effect.

32. Roles in Digestion:

• Saliva: Contains amylase for carbohydrate digestion.
• Hydrochloric acid: In the stomach, it kills bacteria and activates pepsin for protein digestion.
• Bile: Emulsifies fats, aiding in their digestion and absorption in the small intestine.

Section C: Long Answer Questions

33. Human Respiratory System and Alveoli:

• a.
• b. Alveoli have a large surface area due to their balloon-like structure, thin walls for easy gas diffusion, and are surrounded by capillaries for gas exchange. The moist surface aids in gas dissolution.

34. Chemical Bonding:

• a. Chemical bonding is the joining of atoms to form molecules.
  • Ionic bonding: Transfer of electrons, e.g., NaCl (sodium chloride).
  • Covalent bonding: Sharing of electrons, e.g., H₂O (water).
• b. Elements form bonds to achieve a stable electron configuration, usually to complete their outer electron shell.

35. Electric Motor:

• a. [Diagram showing coil, magnets, commutator, and power supply]
  • An electric motor converts electrical energy into mechanical energy through the interaction of magnetic fields.
• b. Efficiency can be improved by using stronger magnets, reducing friction with better bearings, or optimizing the coil design.

36. Double Circulation in Humans:

• a. Human heart pumps blood in two circuits: pulmonary (to lungs for oxygenation) and systemic (to body for nutrient supply). Advantages include efficient oxygen supply and better pressure management.
• b. One-way flow is ensured by valves like the tricuspid, mitral, aortic, and pulmonary valves that prevent backflow.

37. Asexual Reproduction in Plants:

• a. Types include vegetative propagation, budding, fragmentation, and spore formation.
  • Vegetative Propagation: New plants from parts like stems or roots, e.g., potatoes grow from tubers.
• b.Sexual: Provides genetic variation through mixing of genes, useful for adaptation.
  • Asexual: Ensures genetic uniformity, quick reproduction, no need for a mate, but limited genetic diversity.

38. Liver Functions:

• a. The liver detoxifies chemicals, produces bile for fat digestion, stores glycogen, regulates blood composition, and metabolizes nutrients.
• b. Liver detoxifies by converting harmful substances into less toxic or water-soluble compounds, which are then excreted. It uses enzymes for this process.

39. Acid Rain:

• a. Acid rain, from pollutants like SO₂ and NOₓ, harms ecosystems by acidifying water bodies, damaging forests, and eroding buildings. It affects soil pH, reducing its fertility.
• b. Mitigation includes reducing emissions through cleaner industrial processes, using alternative energy sources, and employing techniques like liming to neutralize soil acidity.