Nutrition
Plant and Animal Nutrition; Balanced Diet
Overview
Nutrition is the process by which living organisms obtain and utilize food for energy, growth, repair, and maintenance of life processes. This topic bridges biology fundamentals with practical health knowledge, making it a favourite in Assam TET Paper II science sections.
For the exam, you must understand two distinct nutritional modes—autotrophic (plants) and heterotrophic (animals)—along with the digestive system in humans, and the concept of a balanced diet. Questions typically test definitions, functions of nutrients, digestive organs, and deficiency diseases.
Mastering nutrition requires clarity on photosynthesis mechanisms, the human digestive pathway, and the role of each nutrient class. Assam-specific elements like local food sources (rice, fish, leafy greens, bamboo shoots) occasionally appear in application-based questions.
Key Concepts
- Autotrophic Nutrition: Organisms (mainly green plants) synthesize their own food from inorganic substances using sunlight. Photosynthesis is the key process: carbon dioxide + water → glucose + oxygen in the presence of chlorophyll and light.
- Heterotrophic Nutrition: Organisms (animals, fungi, most bacteria) depend on other organisms for food. Types include holozoic (ingestion of solid food), saprophytic (feeding on dead matter), and parasitic (living on/in a host).
- Photosynthesis Equation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. Chlorophyll in chloroplasts captures light; stomata allow gas exchange.
- Human Digestive System: A continuous alimentary canal—mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus—with accessory glands (salivary glands, liver, pancreas).
- Enzymes and Digestion: Saliva contains amylase (starch → maltose); gastric juice contains pepsin (proteins → peptones); pancreatic juice contains lipase, trypsin, amylase; intestinal juice completes digestion.
- Absorption and Assimilation: Villi in the small intestine absorb nutrients into blood; absorbed food is used for energy or building body tissues.
- Balanced Diet: A diet containing carbohydrates, proteins, fats, vitamins, minerals, roughage, and water in correct proportions for age, sex, and activity level.
- Deficiency Diseases: Lack of specific nutrients causes diseases—scurvy (vitamin C), rickets (vitamin D), night blindness (vitamin A), anaemia (iron), goitre (iodine), kwashiorkor (protein), marasmus (protein-energy).
Formulas / Key Facts
| Nutrient | Main Function | Rich Sources | Deficiency Disease |
|---|---|---|---|
| Carbohydrates | Energy (4 kcal/g) | Rice, wheat, potato | Fatigue, weakness |
| Proteins | Growth and repair (4 kcal/g) | Pulses, fish, eggs, milk | Kwashiorkor, marasmus |
| Fats | Energy storage (9 kcal/g) | Oil, ghee, nuts | Weight loss, skin problems |
| Vitamin A | Vision, immunity | Carrot, papaya, liver | Night blindness |
| Vitamin B₁ | Nerve function | Whole grains | Beriberi |
| Vitamin C | Wound healing, immunity | Citrus fruits, amla | Scurvy |
| Vitamin D | Calcium absorption, bones | Sunlight, fish oil | Rickets (children), osteomalacia (adults) |
| Calcium | Bones and teeth | Milk, green leafy vegetables | Weak bones |
| Iron | Haemoglobin formation | Spinach, jaggery, meat | Anaemia |
| Iodine | Thyroid hormone synthesis | Iodized salt, seafood | Goitre |
Photosynthesis requirements: Carbon dioxide, water, chlorophyll, sunlight.
Site of photosynthesis: Chloroplasts (in mesophyll cells of leaves).
Largest digestive gland: Liver (produces bile for fat emulsification).
Roughage/Fibre: Provides no nutrients but aids bowel movement; sources include vegetables, whole grains.
Worked Examples
Example 1: Photosynthesis Identification
Question: A green plant kept in a dark room for 48 hours is then exposed to sunlight with one leaf covered by black paper. After a starch test, which part of the leaf will show blue-black colour with iodine?
Solution:
- Step 1: Darkness for 48 hours removes stored starch from leaves.
- Step 2: Only the uncovered part receives sunlight and performs photosynthesis.
- Step 3: Starch is produced only where light reaches.
- Step 4: Iodine turns blue-black in presence of starch.
- Answer: Only the uncovered/exposed part of the leaf shows blue-black colour.
Example 2: Digestive Enzyme Action
Question: What happens to a piece of bread when chewed for 2–3 minutes? Why does it taste sweet?
Solution:
- Step 1: Bread contains starch (a complex carbohydrate).
- Step 2: Saliva in the mouth contains the enzyme salivary amylase (ptyalin).
- Step 3: Amylase breaks down starch into maltose (a simple sugar).
- Step 4: Maltose tastes sweet.
- Answer: Prolonged chewing allows salivary amylase to convert starch into maltose, giving a sweet taste.
Example 3: Balanced Diet Planning
Question: A child in Assam shows poor growth, swollen belly, and thin limbs. Identify the deficiency and suggest dietary corrections.
Solution:
- Step 1: Symptoms (poor growth, swollen belly, thin limbs) indicate protein deficiency.
- Step 2: The condition is likely Kwashiorkor.
- Step 3: Diet should include protein-rich foods available locally—fish, eggs, pulses (dal), milk, soybean.
- Answer: The child suffers from Kwashiorkor (protein deficiency). Include fish, eggs, dal, and milk in daily diet.
Common Mistakes
❌ Confusing photosynthesis with respiration → Photosynthesis produces oxygen and glucose using CO₂ (only in light, in green parts); respiration consumes oxygen and glucose to release energy (in all living cells, continuously).
❌ Thinking only leaves perform photosynthesis → Any green part containing chlorophyll can photosynthesize (green stems, sepals, unripe fruits).
❌ Believing fats are always harmful → Fats are essential for energy storage, insulation, and vitamin absorption. Only excess fat causes health problems.
❌ Mixing up Kwashiorkor and Marasmus → Kwashiorkor: protein deficiency (swollen belly, thin limbs). Marasmus: overall protein-energy deficiency (extreme thinness, wrinkled skin).
❌ Assuming vitamins provide energy → Vitamins and minerals are regulatory substances; they do not provide calories. Only carbohydrates, proteins, and fats provide energy.
❌ Ignoring the role of water and roughage → Both are essential components of a balanced diet though they provide no energy. Water aids metabolism; roughage prevents constipation.
Quick Reference
- Photosynthesis formula: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂ (chlorophyll required).
- Energy values: Carbohydrates and proteins = 4 kcal/g; Fats = 9 kcal/g.
- Vitamin D is the "sunshine vitamin"—synthesized in skin on sun exposure.
- Bile emulsifies fats but contains no enzymes; produced by liver, stored in gall bladder.
- Villi in small intestine increase surface area for nutrient absorption.
- Iodized salt prevents goitre—a government public health initiative.