CBSE Class 10th Science Practice Paper

Section A: Multiple Choice Questions (MCQs)

1. B) Oxygen - Oxygen is not a greenhouse gas as it does not trap heat in the atmosphere like CO₂, CH₄, or N₂O.
2. B) Fermentation - Fermentation converts sugar into alcohol, CO₂, and energy in the absence of oxygen.
3. A) 0.5 D - Power of a lens (in dioptres) = 1/focal length (in meters). So, for a focal length of 20 cm (0.20 m), Power = 1/0.20 = 5 D, but if the question specifies 0.5 D, it could be due to a misprint or another context not given.
4. C) NaCl - Common salt is sodium chloride, chemically known as NaCl.
5. C) Wind - Wind energy is renewable as it's sourced from the natural movement of air, constantly replenished by solar energy.
6. C) Medulla oblongata - This part of the brain stem controls involuntary actions like breathing and heartbeat.
7. C) Retina - The image of an object is formed on the retina, which converts light into neural signals.
8. B) Ovary - Fertilization in plants takes place in the ovary where the ovule is located.
9. B) Ampere - Electric current is measured in amperes (A).
10. B) Plastic - Plastic does not decompose naturally over time, hence it's not biodegradable.
11. A) 7 - Pure water is neutral with a pH of 7.
12. B) Mercury - Mercury is the only metal that is liquid at room temperature.
13. C) Cytokinin - Cytokinins are plant hormones known for promoting cell division.
14. B) It absorbs UV radiation - The ozone layer protects earth by absorbing most UV radiation from the sun.
15. B) Area of cross-section - Resistance (R) is inversely proportional to the area of cross-section (A) of a conductor (R ∝ 1/A).
16. C) White flower and purple flower - Mendel studied contrasting traits, like flower color, in peas.
17. C) Condensation - When gas cools and changes to liquid, it's known as condensation.
18. C) HCl - HCl is hydrochloric acid, not a base.
19. C) Dispersion - The splitting of white light into its colors is called dispersion.
20. C) Scales on feet - Scales on feet are not adaptations for flight but for grip or protection.

Section B: Short Answer Questions

21. How the human ear converts sound waves into electrical signals:

• Sound waves travel down the auditory canal and vibrate the eardrum. These vibrations are passed through the ossicles (hammer, anvil, and stirrup) to the cochlea. Inside the cochlea, the vibrations move the fluid, which causes hair cells to bend. This bending generates electrical impulses that are transmitted via the auditory nerve to the brain, where they are interpreted as sound.

22. Differences between aerobic and anaerobic respiration:

• Aerobic Respiration: Requires oxygen, occurs in mitochondria, yields 36-38 ATP per glucose, produces CO₂ and H₂O.
• Anaerobic Respiration: No oxygen needed, happens in cytoplasm, produces 2 ATP per glucose, results in lactic acid in humans or ethanol and CO₂ in yeast.

23. Definition and change of pH:

• pH is a measure of the acidity or basicity of an aqueous solution, defined as the negative logarithm of the hydrogen ion concentration. When an acid is added to water, it dissociates to increase the concentration of H⁺ ions, lowering the pH, making the solution more acidic.

24. Role of the pituitary gland:

• The pituitary gland regulates growth, metabolism, and reproductive processes by secreting hormones like growth hormone, thyroid-stimulating hormone, FSH, LH, etc. It's often called the 'master gland' as it influences other endocrine glands.

25. Ohm's Law:

• Ohm's Law states V = IR, where V is voltage, I is current, and R is resistance. It's used to calculate current by dividing voltage by resistance in a circuit.

26. Chalk sound phenomenon:

• The sound produced by chalk varies with the amplitude of vibration. Soft strikes produce vibrations with low amplitude, which are below the hearing threshold when the chalk is close to the ear. Harder strikes increase the amplitude, making the sound louder and audible.

27. Mendel's Law of Segregation:

• This law states that during gamete formation, the allele pairs separate (segregate) so that each gamete carries only one allele for each gene. This explains how traits are passed from parents to offspring, with each new individual receiving one allele from each parent.

28. Phototropism in plants:

• Phototropism is the growth or movement of a plant in response to light. Auxin, a plant hormone, accumulates on the side away from light, causing cells on that side to elongate more, thus bending the plant towards the light source.

29. Renewable vs. Non-renewable resources:

• Renewable: Resources that can replenish naturally over time, e.g., solar energy, which is constantly available from the sun.
• Non-renewable: Resources that are finite, like coal, which, once depleted, cannot be replaced within human timescales.

30. Balanced chemical equation:

• NaOH + HCl → NaCl + H₂O

31. Function and depletion of the ozone layer:

• The ozone layer absorbs most of the Sun's UV radiation, preventing it from reaching and damaging life on Earth. Human activities, particularly the release of CFCs, deplete this layer, leading to increased UV levels which can harm living organisms.

32. Role of the pancreas in digestion:

• The pancreas secretes pancreatic juices into the small intestine, which contain enzymes like amylase for starch digestion, lipase for fats, and proteases for proteins, aiding in the breakdown of food.

Section C: Long Answer Questions

33. Female Reproductive System and Fertilization:

• a.
• b. Fertilization occurs when a sperm penetrates an egg in the fallopian tube. The sperm must travel through the cervix and uterus. Once fertilization happens, the zygote travels to the uterus for implantation.

34. Electrolysis and Electrolytes:

• a. Electrolysis is the process of using electric current to cause a chemical reaction that would not occur spontaneously. Applications include:
  • Purification of metals like copper
  • Electroplating for decorative or protective coatings
• b.Electrolytes: Conduct electricity when dissolved or melted due to the presence of ions (e.g., NaCl in water).
  • Non-electrolytes: Do not conduct electricity as they do not ionize in solution (e.g., sugar).

35. Reflection, Refraction, Eye Adjustment:

• a. Reflection: When light strikes a surface, it bounces back. 

  

  • Refraction: Light bends when moving from one medium to another due to a change in speed. 

    

• b. The eye adjusts focus through the ciliary muscles which alter the lens's curvature - less curved for distant objects and more for close ones.

36. Carbon Cycle:

• a. [Labeled diagram showing photosynthesis, respiration, decomposition, combustion, and fossil fuel formation.]
• b. The carbon cycle is crucial for regulating atmospheric CO₂, maintaining Earth's temperature, providing carbon for photosynthesis, and ensuring a balance in natural systems.

37. Homologous Series:

• a. A homologous series in organic chemistry consists of compounds with the same functional group and similar chemical properties, differing by -CH₂- in their structure. Example: Alkanes.
• b.
  • Methane (CH₄)
  • Ethane (C₂H₆)
  • Propane (C₃H₈)
  • Butane (C₄H₁₀)

38. Magnetic Effect of Electric Current:

• a. Experiment: When current flows through a wire, it can be shown by placing a compass near the wire; the needle deflects, demonstrating magnetism due to electric current. [Simple setup diagram]
• b. An electric fuse contains a metal strip or wire that melts when current exceeds the safe level, breaking the circuit to prevent damage or fire.

39. Anaerobic Respiration in Yeast:

• a. Yeast undergoes fermentation, converting glucose into ethanol and CO₂ under anaerobic conditions, producing 2 ATP per glucose. This process is used in brewing and baking.
• b.Aerobic vs. Anaerobic: Aerobic respiration yields significantly more ATP (36-38 per glucose) with oxygen, while anaerobic produces only 2 ATP without oxygen. However, anaerobic respiration allows energy production in the absence of oxygen, which is vital for some organisms.