Chapter Overview & Weightage
Nutrition in Plants is Chapter 1 of CBSE Class 7 Science and sets the foundation for understanding how living organisms obtain energy. This chapter regularly contributes 10–12 marks in the annual exam through a mix of objective and descriptive questions.
Expect 1-mark questions on definitions (photosynthesis, autotroph, parasite), 2-mark questions on differences (autotroph vs. heterotroph), and 3-mark questions on the process of photosynthesis and types of nutrition. Diagram of a leaf with chloroplasts is frequently asked.
Key Concepts You Must Know
Mode of nutrition: The way an organism obtains its food.
Autotrophs: Organisms that prepare their own food from simple inorganic substances. Plants, algae, and some bacteria are autotrophs. The prefix “auto” means self — they are self-feeders.
Heterotrophs: Organisms that depend on other organisms for food. All animals, fungi, and most bacteria are heterotrophs.
Photosynthesis: The process by which green plants make food using sunlight, carbon dioxide, and water. Chlorophyll in leaves absorbs sunlight.
Chlorophyll: The green pigment present in chloroplasts (special cell structures). It is responsible for capturing light energy and giving plants their green colour.
Stomata: Tiny pores on the surface of leaves through which gas exchange occurs — CO₂ enters and O₂ exits during photosynthesis.
Parasitic plants: Plants that depend on other plants (hosts) for nutrition. Examples: Cuscuta (Amarbel), Loranthus.
Insectivorous plants: Plants that trap and digest insects to supplement their nitrogen supply. Examples: Venus flytrap, pitcher plant (Nepenthes), sundew.
Saprotrophic nutrition: Obtaining nutrition from dead and decaying organic matter. Fungi (bread mould, mushroom) and some bacteria are saprotrophs.
Important Concepts
In words: Carbon dioxide + Water → Glucose + Oxygen
Inputs: CO₂ (from air through stomata), H₂O (from soil through roots), Sunlight, Chlorophyll
Output: Glucose (food/energy), Oxygen (released into air)
All four must be present:
- Sunlight (source of energy)
- Chlorophyll (to absorb light)
- Carbon dioxide (from air)
- Water (from soil)
Solved Previous Year Questions
PYQ 1 — Fill in the blanks / short answer (1-mark)
Q: The process of preparing food in green plants is called ______.
Answer: Photosynthesis.
PYQ 2 — Short answer (2-mark)
Q: Differentiate between autotrophic and heterotrophic nutrition with one example of each.
Answer:
| Feature | Autotrophic | Heterotrophic |
|---|---|---|
| Food preparation | Make their own food | Depend on others |
| Raw materials used | CO₂, H₂O, sunlight | Organic food from outside |
| Example | Green plants (mango tree) | Animals (cow), fungi |
PYQ 3 — Descriptive (3-mark)
Q: Explain the process of photosynthesis. Name the raw materials required.
Answer: Photosynthesis is the process by which green plants prepare food using sunlight.
Raw materials: Carbon dioxide (CO₂) from the air enters leaves through stomata. Water (H₂O) is absorbed from the soil by roots and transported to leaves. Sunlight provides energy, absorbed by chlorophyll.
The plant converts CO₂ and H₂O into glucose (food) and releases oxygen as a by-product. The glucose is stored as starch in the plant.
Chemical equation:
Difficulty Distribution
| Level | Examples | Marks |
|---|---|---|
| Easy | Definitions, fill in blanks, identify autotroph/heterotroph | 1 |
| Medium | Process of photosynthesis, differences, conditions for photosynthesis | 2–3 |
| Hard | Explain parasitic/insectivorous nutrition with examples, diagram questions | 3–5 |
Expert Strategy
This chapter has high-recall demand — write short, clear definitions and memorise the photosynthesis equation cold. The equation comes up in every exam in some form (fill in the blank, label the products, or write the balanced equation).
For diagram questions, the key is labelling: chloroplast, stomata, guard cells, mesophyll cells. Practice drawing a labelled cross-section of a leaf.
For insectivorous plants, remember WHY they eat insects — they grow in nitrogen-poor soil (bogs, marshes) and supplement their nitrogen through insect digestion. This “why” earns marks in “give reasons” type questions.
Common Traps
Trap 1: Saying plants don’t respire. Plants do respire (they also produce CO₂) — but during daylight, photosynthesis takes in far more CO₂ than respiration releases, making the net exchange look like CO₂ intake only. At night, only respiration occurs.
Trap 2: Saying oxygen comes from CO₂ in photosynthesis. The oxygen released during photosynthesis comes from the splitting of water molecules (H₂O), not from CO₂. This is a Class 10–11 detail, but mentioning it at Class 7 level impresses teachers.
Trap 3: Confusing Cuscuta with an insectivorous plant. Cuscuta (dodder/Amarbel) is a parasitic plant — it twines around host plants and absorbs their nutrients. It does NOT trap insects. Insectivorous plants (Venus flytrap) trap insects. These are two different modes of heterotrophic nutrition.
Trap 4: Fungi are often mistakenly classified as plants. Fungi are NOT plants — they don’t have chlorophyll and cannot photosynthesise. They are saprotrophs, feeding on dead organic matter by secreting digestive enzymes outside and absorbing the nutrients.