Grade 10 biology Anatomy and Physiology of Plants – Nutrition Notes

Biology — Anatomy & Physiology of Plants

Subtopic: Nutrition (for learners age ~15)

1. Types of nutrition in plants

Plants obtain nutrients in different ways. Main types:

• Autotrophic (photosynthetic) — make their own food from water, carbon dioxide and light energy (most green plants: maize, sugarcane, cassava, beans). Equation:
  6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂
• Heterotrophic (parasitic) — obtain food from living hosts. Kenyan examples: Striga (witchweed) attacks maize and sorghum; mistletoe grows on trees and takes water and nutrients.
• Insectivorous / carnivorous — trap and digest insects to supplement minerals where soil is poor (e.g., sundew, pitcher-like plants in wet habitats).
• Saprophytic / decomposer feeders — rare among true plants; many organisms that live on dead organic matter are fungi. (Mention: some non-photosynthetic plants rely on fungi to obtain nutrients.)
• Mixotrophic — combine photosynthesis with other feeding methods (some plants photosynthesise but also obtain nutrients from host or insects).

2. Chloroplast: structure & function

Chloroplasts are the organelles where photosynthesis happens. Below is a simple labelled diagram and short notes linking parts to function.

• Envelope membranes: control movement of substances into/out of chloroplast.
• Stroma: fluid inside; site of the Calvin (dark) reactions where CO₂ is fixed to make sugars.
• Thylakoid membranes: folded membranes containing chlorophyll and other pigments; site of the light reactions where light energy is captured and used to produce ATP, NADPH and O₂.
• Grana: stacks of thylakoids increase surface area for light capture — more pigment, more light absorption, greater photosynthetic capacity (important in leafy crops like maize and sugarcane).

3. Light and dark stages of photosynthesis (simple illustration)

Photosynthesis happens in two main stages:

4. Significance of photosynthesis

• Produces food (carbohydrates) — basis of food webs and agriculture (maize, beans, potatoes, tea).
• Produces oxygen — essential for respiration of animals and humans.
• Removes CO₂ from the atmosphere — helps reduce greenhouse gases and climate change.
• Provides raw materials for industry: timber, fibres, ethanol and other biofuels.
• Supports soil fertility indirectly — plant growth and crop residues return organic matter to soils.

Suggested learning experiences (practical, local and safe)

1. Practical: Test for starch in a variegated leaf (e.g., a leaf with green and white patches). Steps (simple):
   • Destarch plant by keeping it in the dark overnight.
   • Expose leaf to sunlight for some hours.
   • Remove leaf, boil in water (to break cell walls) then in alcohol (to remove chlorophyll) — use care & adult supervision.
   • Rinse and add iodine — blue-black shows starch where photosynthesis occurred (green patches should have starch; white patches not).
   Learning: links chlorophyll presence to sugar (starch) production.
2. Pondweed oxygen experiment (rate of photosynthesis vs light intensity):
   • Use Elodea or local pondweed inside a test tube or beaker of water, place in sunlight or under a lamp, count bubbles per minute or collect gas over a measuring cylinder.
   • Change distance of lamp or use shade to show effect of light intensity and record results.
3. Field visit to school farm or local tea/maize farm:
   • Observe healthy vs Striga-infected maize; discuss how parasites affect nutrition and crop yields.
   • Collect different leaves and classify as autotrophic, parasitic or insectivorous where available.
4. Group activity: Build a model of a chloroplast using cardboard, green cellophane (for membranes), stacked paper discs for grana; label parts and explain functions to class.
5. Investigation project: Test how CO₂ availability affects photosynthesis (e.g., cover a leafy shoot with a clear plastic bag for a short time and notice condensation; discuss CO₂ & respiration effects). Always supervise and ensure plant safety.
6. Discussion & real-life link: How photosynthesis supports Kenyan agriculture (maize, tea, sugarcane), forests, and livelihoods; role in reducing atmospheric CO₂ and climate resilience.