Integrated Science — Living Things and Their Environment

Subtopic: Nutrition in Plants (Age: 14 — Kenyan context)

In this lesson we learn how plants get their food, the different types of plant nutrition and why it matters for farming and the environment in Kenya. Examples include maize, tea, sugarcane, cassava, and native trees.

1. What is nutrition?

Nutrition is the process by which living organisms obtain and use food for growth, energy and repair. Plants can make their own food or obtain it from other sources.

2. Types of nutrition in plants

• Autotrophic nutrition — plants make their own food (most green plants).
• Heterotrophic nutrition — some plants obtain food from other organisms (parasitic plants, saprophytes, insectivorous plants).

3. How green plants make food: Photosynthesis

Photosynthesis is the process by which green plants use sunlight to convert carbon dioxide and water into glucose (a sugar) and oxygen. It happens mainly in leaves where chlorophyll is found.

4. Where photosynthesis happens

Photosynthesis occurs in chloroplasts (organelles) inside leaf cells. Chlorophyll, the green pigment, traps sunlight.

5. Simple leaf cross-section (visual)

Below is a simplified diagram of a leaf showing parts important for photosynthesis.

6. Factors affecting photosynthesis (and farming tips)

• Light intensity: more light (up to a point) increases photosynthesis. Farmers plant crops where light is sufficient; shade trees reduce yields for some crops.
• Carbon dioxide: plants need CO2. Open fields have enough CO2; glasshouses sometimes increase CO2 to raise yields.
• Water: needed for photosynthesis and to transport minerals. In dry seasons, crops suffer. Mulching and irrigation help (common practice in Kenyan small-scale farming).
• Temperature: affects enzyme activity. Very low or very high temperatures slow photosynthesis. Plant crops in suitable seasons.
• Chlorophyll/leaf health: pests, diseases and nutrient deficiencies (especially lack of nitrogen) reduce chlorophyll and lower photosynthesis.

7. Other types of plant nutrition

• Parasitic plants: obtain water and food from other plants (example: some mistletoe species that grow on trees).
• Saprophytic plants/fungi: get food from dead organic matter (fungi like some mushrooms). Note: fungi are not green and do not photosynthesise.
• Insectivorous (carnivorous) plants: capture insects and digest them to get nutrients where soil is poor (rare in Kenya, but similar plants exist in some wet, nutrient-poor areas).

8. Transport and storage of food in plants

- Translocation: sugars made in leaves are transported to other parts by phloem.
- Xylem carries water and minerals from roots to leaves.
- Storage organs: tubers and roots store food (examples: Irish potato, sweet potato, cassava, yam, sugarcane stores sugar in stems).

9. Simple classroom experiment: Test a leaf for starch (shows photosynthesis happened)

Materials: green leaves (one from a plant kept in sunlight, one kept in shade), boiling water, ethanol (or rubbing alcohol), iodine solution, a hot water bath, white tile or plate, tongs, safety gloves.

1. Boil the leaf in water for 1 minute to soften it (kills leaf and stops chemical reactions).
2. Put the leaf in ethanol and place in a hot water bath until it becomes decolourised (removes chlorophyll).
3. Rinse leaf briefly in warm water, spread on a white plate and add a few drops of iodine solution.
4. If the leaf turns blue-black, starch is present (photosynthesis produced sugar that was stored as starch). A pale brown means little or no starch.

Expected result: the sunlight leaf will test positive for starch; the shaded leaf may show less or no starch.

10. Class activity / Fieldwork ideas

• Compare leaves from plants in sun and shade (starch test).
• Observe stomata using a microscope (peel lower epidermis or use clear nail polish to make an impression).
• Visit a farm to see how farmers manage light, water and spacing to increase crop yields.

11. Summary (key points)

• Most plants are autotrophs — they make their own food by photosynthesis in leaves.
• Photosynthesis requires light, water, carbon dioxide and chlorophyll and produces glucose and oxygen.
• Food is transported in the phloem and stored in roots, tubers or stems.
• Some plants are parasitic, saprophytic or insectivorous and do not rely fully on photosynthesis.

12. Important terms (glossary)

Chlorophyll, Chloroplast, Photosynthesis, Autotrophic, Heterotrophic, Stoma (stomata), Xylem, Phloem, Translocation, Starch.

13. Short quiz (for revision)

1. Write the word equation for photosynthesis.
2. State two factors that affect photosynthesis.
3. Give two examples of food storage organs in plants grown in Kenya.
4. What is the role of stomata?
5. Name one parasitic plant and one saprophytic organism.

Answers

1. Carbon dioxide + Water —(light + chlorophyll)—> Glucose + Oxygen.
2. Examples: light intensity, water availability, carbon dioxide concentration, temperature, health of leaves (chlorophyll).
3. Examples: cassava (root), sweet potato (tuberous root), Irish potato (tuber), sugarcane (stem stores sugar).
4. Stomata allow gases (CO2 in, O2 out) and water vapour to pass; they help in gas exchange and transpiration.
5. Parasitic plant example: mistletoe (on trees). Saprophytic organism example: mushroom (fungus).

Prepared for Integrated Science learners (Kenya). Try the experiments with teacher supervision and follow safety rules when using hot water and chemicals.