Nutrition in Plants

All living organisms need food for energy, growth and repair. Green plants make their own food, so their mode of nutrition is autotrophic, while animals and most other organisms depend on plants directly or indirectly and are heterotrophs. Leaves are the food factories of plants. Their green pigment, chlorophyll, captures sunlight, carbon dioxide enters through tiny pores called stomata, and water and minerals reach the leaves from the roots. In photosynthesis, carbon dioxide + water -> carbohydrate + oxygen, in the presence of sunlight and chlorophyll. The carbohydrate is stored as starch, which turns blue-black with iodine. Some plants use other modes. Cuscuta (amarbel) is a parasite that takes food from its host, and the pitcher plant is insectivorous, trapping insects to get nitrogen. Fungi are saprotrophs that absorb nutrients from dead and decaying matter. In symbiosis, two organisms live together and help each other, as in a lichen (an alga and a fungus) and Rhizobium bacteria in the root nodules of pulses, which fix nitrogen and enrich the soil.

Detailed Worksheet: Nutrition in Plants Section A - Definitions (10 marks) 1. Distinguish between autotrophic and heterotrophic nutrition with examples. (2 marks) 2. Define photosynthesis and write its word equation. (2 marks) 3. What are stomata? State two functions. (2 marks) 4. What are saprotrophs? Give two examples. (2 marks) 5. What is symbiosis? Give one example. (2 marks) Section B - Calculations and Applications (15 marks) 6. List the raw materials needed for photosynthesis and state how each reaches the leaf. (3 marks) 7. Classify as autotroph, parasite, insectivorous plant, saprotroph or symbiotic partner: mango tree, Cuscuta, pitcher plant, mushroom, Rhizobium, bread mould. (3 marks) 8. Why do pulses (legumes) not usually need nitrogenous fertilisers? Explain the role of Rhizobium. (3 marks) 9. Leaves of plants like croton are red or brown. Do they carry out photosynthesis? Explain. Also explain how desert plants with spines make food. (3 marks) 10. Why are farmers advised to add manure and fertilisers to fields? Why do plants in forests not need fertilisers? (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram of a leaf showing the stomata and arrows for carbon dioxide entering and oxygen leaving. Add a separate labelled sketch of an open stoma with guard cells. (4 marks) 12. Draw a labelled diagram of Cuscuta growing on a host plant. (3 marks) 13. Draw a labelled diagram of a pitcher plant showing the lid and pitcher. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Paheli tested two potted plants for starch. One was kept in sunlight and the other in the dark for 72 hours. (i) Describe how she tested the leaves with iodine. (ii) What result did she get for each? (iii) What conclusion can she draw? (iv) Why was the plant kept in the dark for 72 hours? (5 marks) 15. Without photosynthesis, life on Earth would not be possible. (i) Why is the Sun called the ultimate source of energy? (ii) How does photosynthesis help animals breathe? (iii) What would happen to food chains without plants? (iv) How is the oxygen balance maintained? (5 marks) 16. Bread left in a moist place develops cottony growth. (i) What is this growth? (ii) How does it get food? (iii) Why does it grow better in warm and humid weather? (iv) How can food be protected from it? (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Use labelled diagrams wherever asked and write word equations with arrows.