### **Solutions to SCIENCE 25 THEORY.pdf** --- #### **SECTION A** **Answer all questions in this section.** --- ### **Question 1(a)** **Figure 1(a): Natural Cycle (Likely the Carbon or Nitrogen Cycle)** **(i) Name the stages labelled A, B, C, and D.** - **A**: Atmosphere (or CO₂ in the carbon cycle) - **B**: Plants (or producers) - **C**: Animals (or consumers) - **D**: Decomposers (or soil) **(ii) Name the processes labelled P, S, and T.** - **P**: Photosynthesis (if carbon cycle) / Nitrogen fixation (if nitrogen cycle) - **S**: Decomposition - **T**: Combustion (or industrial emissions) **(iii) Three human activities that disrupt the cycle:** 1. Burning fossil fuels (increases CO₂). 2. Deforestation (reduces photosynthesis). 3. Overuse of chemical fertilizers (disrupts nitrogen balance). **Marks**: 10 (3 + 3 + 4) --- ### **Question 1(b)** **Figure 1(b): Farming Systems K and L** **(i) Name the farming systems:** - **K**: Shifting cultivation - **L**: Crop rotation **(ii) Reasons for the names:** - **K**: Farmer moves to new land after soil fertility declines. - **L**: Crops are rotated to maintain soil fertility. **(iii) Two importance of System K to the farmer:** 1. Allows soil to recover naturally. 2. Reduces pest buildup. **(iv) Three reasons System K is discouraged:** 1. Deforestation (land clearing). 2. Not sustainable for large populations. 3. Low productivity per unit area. **(v) Crop to improve soil fertility in L:** Legumes (e.g., beans, clover). **Marks**: 10 (2 + 2 + 2 + 3 + 1) --- ### **Question 1(c)** **Figure 1(c): Inclined Plane (Physics)** **(i) Examples of inclined planes:** 1. Ramps for wheelchairs. 2. Roads on hills. 3. Staircases. **(ii) Calculations:** - **Work output** = Force × Distance = 100 N × 5 m = **500 J** - **Work input** = 400 N × 10 m = **4000 J** - **Efficiency** = (Work output / Work input) × 100 = (500/4000) × 100 = **12.5%** **Marks**: 10 (3 + 3 + 2 + 2) --- ### **Question 1(d)** **Figure 1(d): Scientific Principle (Likely Osmosis/Diffusion)** **(i) Principle:** Osmosis (or diffusion). **(ii) Functions of parts II and VI:** - **II**: Semi-permeable membrane (allows selective passage). - **VI**: Water reservoir (provides solvent). **(iii) Materials in set-ups:** - **(a) III**: Sugar solution, salt solution. - **(b) VII**: Distilled water, starch solution. **(iv) Reason flow must not be reversed in A:** Would disrupt equilibrium (e.g., cause backflow). **Marks**: 10 (1 + 2 + 4 + 3) --- #### **SECTION B** **Answer any three questions.** --- ### **Question 2** **(a) Energy Conservation & Calculation:** - **(i) Three conservation methods:** 1. Use LED bulbs. 2. Turn off unused appliances. 3. Insulate homes. - **(ii) Energy used** = Power × Time = 4000 W × 12 h = **48 kWh**. **(b) Acid-Base Indicators:** - **(i) Examples:** Litmus (red/blue), Phenolphthalein (colorless/pink). - **(ii) In orange juice (acidic):** - Litmus: Red. - Phenolphthalein: Colorless. **(c) Green Economy & Greenhouse Gases:** - **(i) Activities:** 1. Reforestation. 2. Recycling programs. - **(ii) Primary greenhouse gases:** CO₂, Methane (CH₄). **(d) Compost Preparation:** Mix kitchen scraps, leaves, and soil; turn periodically for aeration. **Marks**: 20 (7 + 4 + 6 + 3) --- ### **Question 3** **(a) Poultry Feed:** - **(i) Animal products:** Fishmeal, bone meal. - **(ii) Plant products:** Maize, soybeans. **(b) Water Cycle:** Evaporation → Condensation → Precipitation → Runoff/Infiltration. **(c) Mixtures (Air & Vinegar):** - **(i) Components:** - Air: Nitrogen (78%), Oxygen (21%). - Vinegar: Acetic acid, Water. - **(ii) Solvents:** - Air: Nitrogen. - Vinegar: Water. **(d) Jupiter & Outer Planets:** - **(i) No life reasons:** 1. Extreme cold. 2. No solid surface. - **(ii) Outer planets:** Saturn, Uranus. **Marks**: 20 (4 + 6 + 6 + 4) --- ### **Question 4** **(i) Sharpened Knife & Pressure:** - **Explanation:** Reduces surface area → increases pressure (P = F/A). - **Calculation:** \( P = \frac{10 \, \text{N}}{1 \times 10^{-3} \, \text{m}^2} = 10,000 \, \text{Pa} \). **(ii) Soil pH Estimation:** 1. Mix soil with distilled water. 2. Dip pH paper/strip. 3. Compare color to chart. **(iii) Blood Pressure (150/90 mmHg):** - **Significance:** Hypertension (high systolic/diastolic). - **Remedies:** 1. Reduce salt intake. 2. Exercise regularly. 3. Manage stress. **Marks**: 20 (6 + 6 + 8) --- ### **Question 5** **(a) Farming Systems:** - **(i) Organic farming:** No synthetic chemicals. - **(ii) Mixed farming:** Crops + livestock. - **(iii) Mixed cropping:** Multiple crops simultaneously. **(b) Mixture Classification:** - **(i) Oil + water:** Heterogeneous. - **(ii) Salt + water:** Homogeneous. - **(iii) Ethanol + water:** Homogeneous. **(c) Solar Energy & Heat vs. Temperature:** - **(i) Renewable reasons:** 1. Inexhaustible. 2. No pollution. - **(ii) Differences:** 1. Heat = energy; temperature = measure. 2. Heat in joules; temperature in °C. 3. Heat depends on mass; temperature does not. **(d) Nitrogen Cycle Disruptions:** - **(i) Leaching:** Removes nitrates from soil. - **(ii) No legumes:** Reduces nitrogen fixation. **Marks**: 20 (6 + 3 + 5 + 6) ---