Nutrition in Plants - Class 7 Science (CBSE)
Based on the 2025-26 NCERT syllabus for Class 7 Science. This chapter explains how plants make their own food and the different modes of nutrition found in the plant kingdom.
1. Why this chapter matters
Plants are the foundation of all food chains. Understanding how they produce food helps us appreciate the delicate balance of life on Earth. In CBSE exams, this chapter contributes 6-8 marks with a focus on photosynthesis and nutrition types.
2. Photosynthesis
Photosynthesis is the process by which green plants prepare their own food using carbon dioxide, water, sunlight, and chlorophyll.
Equation
Carbon dioxide + Water (in presence of Sunlight and Chlorophyll) = Glucose + Oxygen
6CO2 + 6H2O (sunlight + chlorophyll) = C6H12O6 + 6O2
Requirements for photosynthesis
- Carbon dioxide: Obtained from air through stomata.
- Water: Absorbed from soil through roots.
- Sunlight: Energy source absorbed by chlorophyll.
- Chlorophyll: Green pigment in leaves that traps sunlight energy.
Where does photosynthesis occur?
Photosynthesis occurs in the leaves, specifically in the chloroplasts present in leaf cells.
3. Chloroplast
Chloroplasts are tiny organelles in plant cells that contain chlorophyll. They are the site of photosynthesis.
- Chloroplasts give leaves their green colour.
- They absorb sunlight energy and convert it into chemical energy.
4. Stomata
Stomata (singular: stoma) are tiny pores on the surface of leaves, mainly on the lower surface.
Structure
Each stoma is surrounded by two guard cells that control its opening and closing.
Functions
- Allow carbon dioxide to enter the leaf for photosynthesis.
- Allow oxygen (produced during photosynthesis) to leave.
- Allow water vapour to exit through transpiration.
5. Other modes of nutrition in plants
Autotrophic nutrition
Plants that make their own food using photosynthesis. All green plants are autotrophs.
Heterotrophic nutrition
Some plants cannot make their own food and depend on other organisms for nutrition.
Parasitic plants
These plants live on or inside another living organism (host) and derive nutrition from it.
- Example: Cuscuta (Amarbel) -- a yellow, leafless vine that coils around hosts like neem or hibiscus and sucks nutrients.
- Cuscuta has no chlorophyll and cannot photosynthesise.
Saprophytic plants
These plants obtain nutrition from dead and decaying organic matter.
- Example: Mushrooms, moulds, and other fungi.
- They secrete digestive juices on the dead matter and absorb the nutrients.
Insectivorous plants
These plants trap and digest insects to obtain nutrients, especially nitrogen, because they grow in nitrogen-deficient soil.
| Plant | How it traps insects |
|---|---|
| Pitcher plant | Leaf is modified into a pitcher with a lid. Insects entering slip and fall into digestive fluid |
| Venus flytrap | Leaves snap shut when trigger hairs are touched |
| Sundew | Sticky droplets on leaves trap insects |
| Bladderwort | Underwater bladders trap small aquatic organisms |
6. Saprotrophs
Saprotrophs are organisms that feed on dead and decaying organic matter. They secrete digestive enzymes onto the food and absorb the digested nutrients.
Examples: Fungi (mushrooms, yeast, bread mould), some bacteria.
Importance of saprotrophs
- They act as decomposers in the ecosystem.
- They recycle nutrients back into the soil.
- Without them, dead matter would accumulate.
7. Symbiotic relationship
Some organisms live together and share nutrients. This is called symbiosis.
Rhizobium and legumes
Rhizobium bacteria live in the root nodules of leguminous plants (peas, beans, gram). The bacteria convert atmospheric nitrogen into usable form for the plant. In return, the plant provides food and shelter to the bacteria.
Lichens
Lichens are a symbiotic association between an alga and a fungus. The alga makes food through photosynthesis, and the fungus provides water and minerals.
8. Comparison of nutrition modes
| Mode | Description | Example |
|---|---|---|
| Autotrophic | Makes own food via photosynthesis | All green plants |
| Parasitic | Lives on host, derives nutrients | Cuscuta |
| Saprophytic | Feeds on dead organic matter | Mushrooms |
| Insectivorous | Traps and digests insects | Pitcher plant |
| Symbiotic | Mutual benefit between two organisms | Rhizobium in legume roots |
9. Worked examples
Example 1: Why are leaves green?
Leaves are green because they contain chlorophyll, a green pigment that absorbs sunlight for photosynthesis.
Example 2: How does Cuscuta get its nutrition?
Cuscuta is a parasitic plant. It does not have chlorophyll. It attaches to a host plant with special structures called haustoria and absorbs nutrients from the host's vascular tissue.
Example 3: Why do pitcher plants eat insects?
Pitcher plants grow in soil deficient in nitrogen. They trap and digest insects to obtain the nitrogen they need for growth.
10. Common mistakes and how to fix them
| Mistake | Fix |
|---|---|
| Thinking plants only respire and do not breathe | Plants respire too -- they take in oxygen and release carbon dioxide |
| Confusing stomata with chlorophyll | Stomata are pores; chlorophyll is a pigment |
| Believing all fungi are plants | Fungi are saprotrophs -- they cannot photosynthesise |
| Calling Cuscuta a saprophyte | Cuscuta is a parasite, not a saprophyte (it lives on a living host) |
| Thinking photosynthesis occurs only in leaves | Some stems (cactus) also perform photosynthesis |
11. CBSE exam focus
| Question type | Marks | Frequency |
|---|---|---|
| Photosynthesis equation and requirements | 2-3 marks | 1 question |
| Stomata structure and function | 2 marks | 1 question |
| Heterotrophic nutrition types | 2-3 marks | 1 question |
| Symbiotic relationships | 2 marks | 1 question |
| Insectivorous plants adaptation | 3 marks | Occasional |
12. Self-test
- Write the equation for photosynthesis.
- What is the role of stomata in plants?
- Differentiate between autotrophic and heterotrophic nutrition.
- Name one parasitic plant and one saprophytic plant.
- What is the symbiotic relationship between Rhizobium and leguminous plants?
- Why are insectivorous plants found in nitrogen-deficient soil?
13. Answer key
- CO2 + H2O = C6H12O6 + O2 (in presence of sunlight and chlorophyll).
- Stomata allow exchange of gases (CO2 in, O2 out) and release water vapour during transpiration.
- Autotrophs make their own food; heterotrophs depend on others for food.
- Parasitic: Cuscuta. Saprophytic: Mushroom (or bread mould).
- Rhizobium bacteria live in root nodules, convert nitrogen for plant use. The plant provides food and shelter.
- They cannot get enough nitrogen from the soil, so they trap insects to obtain nitrogen from insect bodies.
14. Quick revision
- Photosynthesis: CO2 + H2O gives glucose + O2 (requires sunlight and chlorophyll).
- Chloroplasts contain chlorophyll, the site of photosynthesis.
- Stomata: tiny pores for gas exchange and transpiration.
- Autotrophs: make their own food (green plants).
- Heterotrophs: depend on others (parasites, saprophytes, insectivores).
- Symbiosis: mutually beneficial relationship (Rhizobium + legumes).
- Saprotrophs: feed on dead organic matter (decomposers).
