Chapter 2 · Question 9
Explain how pH affects plant growth and aquatic life. What is acid rain, and what happens when soil becomes too acidic? Mention how a farmer can treat acidic soil.
Answer
Direct Answer
Plants require a specific pH range for healthy growth and can only survive within a narrow range. Soil pH can be tested (Activity 2.12) by mixing a soil sample with water, filtering, and testing the filtrate with universal indicator paper. Acid rain — rainwater with a pH below 5.6 — flows into rivers, lowering the pH of river water and making survival difficult for aquatic life. If soil is too acidic, a farmer can treat it by adding quicklime (), slaked lime (), or chalk () — all basic substances that neutralise the excess acid in the soil.
Simple Explanation
Plants need the soil pH to stay in a suitable range to grow well. Acid rain is rainwater with pH below 5.6; when it flows into rivers, it lowers the river-water pH and makes life difficult for aquatic organisms. If soil is too acidic, a farmer can add quicklime, slaked lime, or chalk. These basic substances neutralise the excess acidity and bring the soil closer to a plant-friendly range.
Exam-Ready Structure
The pH sensitivity of the natural environment — soil, water bodies, and rainfall — is a critical application of acid-base chemistry in ecology and agriculture, covered in NCERT Class 10 Chapter 2. 1. Living organisms and pH: The human body works within the pH range 7.0 to 7.8, and living organisms can survive only within a narrow range of pH change. 2. Acid rain: (a) When the pH of rainwater falls below 5.6, it is termed acid rain. (b) Impact: When acid rain flows into rivers, it lowers the pH of river water. This makes survival difficult for aquatic life. 3. Soil pH and plants: (a) Plants require a specific pH range for healthy growth. (b) To find the pH required for healthy plant growth in a region, one can collect soil from different places, note the plants growing there, mix about 2 g of soil with 5 mL of water in a test tube, shake, filter, and test the filtrate with universal indicator paper (Activity 2.12). 4. Treatment of acidic soil: If soil is too acidic, farmers use basic substances to neutralise soil acidity: quicklime (calcium oxide, ), slaked lime (calcium hydroxide, ), or chalk (calcium carbonate, ).
Key Points
- Living beings survive within a narrow pH range, typically 7.0 to 7.8
- Acid rain: rainwater with pH below 5.6 (normal rain ~5.6 due to dissolved CO₂)
- Acid rain lowers river pH, harming aquatic life
- Soil pH test (Activity 2.12): mix soil with water, filter, test filtrate with universal indicator
- Treatment for acidic soil: add quicklime (), slaked lime (), or chalk ()
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