Nutrition in Plants and Animals
Nutrition: An Introduction
Nutrition is the process by which organisms obtain and utilize food for energy, growth, and maintenance. All living organisms need nutrients — substances that provide energy and materials for repair and growth.
Modes of Nutrition
| Type | Organisms | How it Works |
|---|---|---|
| Autotrophic | Green plants, some bacteria | Make their own food using light (photosynthesis) or chemical energy |
| Heterotrophic | Animals, fungi, most bacteria | Cannot make their own food — depend on other organisms |
| Saprophytic | Fungi, some bacteria | Feed on dead and decaying matter |
| Parasitic | Tapeworm, leeches | Feed on living organisms |
Autotrophic Nutrition: Photosynthesis
Photosynthesis is the process by which green plants convert light energy into chemical energy (glucose). It occurs in chloroplasts (mainly in leaves).
Overall Equation: 6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ + 6O₂ (Carbon dioxide + Water + Light → Glucose + Oxygen)
Two Stages:
1. Light-dependent reactions (Photochemistry):
- Occur in the thylakoid membranes
- Chlorophyll absorbs light (mainly red and blue wavelengths — green is reflected, which is why plants appear green)
- Water is split (photolysis): 2H₂O → 4H⁺ + 4e⁻ + O₂
- ATP and NADPH are produced
- Oxygen is released as a byproduct
2. Light-independent reactions (Dark reactions / Calvin Cycle):
- Occur in the stroma of chloroplasts
- CO₂ is captured and reduced using ATP and NADPH (from light reactions)
- CO₂ is fixed into glucose via the Calvin cycle (C3 pathway)
- Three-carbon compounds (3-PGA) are the first stable product
Chlorophyll: The green pigment that absorbs light energy. It is located in the thylakoid membranes of chloroplasts. Structurally, chlorophyll contains a porphyrin head and a phytol tail.
Factors Affecting Photosynthesis
- Light intensity: More light → more photosynthesis (up to a point)
- Carbon dioxide concentration: More CO₂ → more photosynthesis (current ambient ~0.04%)
- Temperature: Optimal around 25–35°C — enzymes denature beyond this
- Water: Essential raw material; deficiency causes wilting and reduces photosynthesis
- Mineral nutrients: Nitrogen (for chlorophyll), magnesium (central atom in chlorophyll), phosphorus (for ATP)
Heterotrophic Nutrition in Animals
Animals cannot make their own food. They must ingest and digest food.
Human Digestive System
The human digestive system is a 9-meter long tube with accessory organs. It follows this sequence:
Mouth/Buccal Cavity:
- Ingestion: Food enters
- Salivary amylase (ptyalin) begins starch digestion → maltose
- Mechanical digestion: Teeth grind food (mastication)
- Tongue: Mixes food with saliva and forms bolus
Pharynx and Esophagus:
- Swallowing: Bolus moves down pharynx
- Peristalsis: Involuntary waves of muscle contraction push food down esophagus
- No digestion occurs here
- Lower esophageal sphincter (LES) prevents backflow
Stomach:
- Capacity: ~1–1.5 litres
- Gastric juice secreted by gastric glands:
- HCl: Kills bacteria, provides acidic medium (pH ~2)
- Pepsin: Digests proteins → peptones (secreted as pepsinogen, activated by HCl)
- Mucus: Protects stomach wall from HCl
- Food stays in stomach 1–5 hours (semi-liquid called chyme)
- Intrinsic factor: Secreted by parietal cells — needed for vitamin B12 absorption
Small Intestine (duodenum, jejunum, ileum — ~6 metres):
- Most digestion occurs here
- Pancreatic enzymes (from pancreas via pancreatic duct):
- Trypsin: Digests proteins
- Amylase: Digests starch
- Lipase: Digests fats → fatty acids + glycerol
- Sodium bicarbonate: Neutralizes HCl in chyme
- Bile (from liver, stored in gallbladder): Emulsifies fats (large globules → tiny droplets) — increases surface area for lipase action
- Intestinal enzymes (from villi epithelium):
- Maltase: Maltose → glucose
- Sucrase: Sucrose → glucose + fructose
- Lactase: Lactose → glucose + galactose
- Peptidases: Polypeptides → amino acids
Absorption in Small Intestine:
- Villi and microvilli increase surface area (finger-like projections)
- Single layer of cells for easy absorption
- Lacteals (lymph vessels in villi) absorb fats; blood capillaries absorb glucose and amino acids
Large Intestine (colon, caecum, rectum — ~1.5 metres):
- Water and mineral salt absorption
- Stores undigested food (feces) temporarily
- Bacteria: E. coli present — synthesize vitamin K and some B vitamins
- Appendix: Vestigial organ, sometimes gets infected (appendicitis)
Rectum and Anus:
- Feces stored in rectum
- Egestion: Expelled through anus
Nutrients and Their Functions
| Nutrient | Function | Sources |
|---|---|---|
| Carbohydrates | Main energy source (4 kcal/g) | Rice, wheat, sugar |
| Proteins | Growth and repair (4 kcal/g) | Pulses, eggs, meat |
| Fats | Energy storage, insulation (9 kcal/g) | Ghee, oil, nuts |
| Vitamins | Regulate body processes | Fruits, vegetables |
| Minerals | Bones, blood, nerves | Milk, leafy vegetables |
| Water | Transport, chemical reactions | Drinking water |
Deficiency Diseases
| Deficiency | Disease | Symptoms |
|---|---|---|
| Vitamin A | Night blindness, Xerophthalmia | Cannot see in dim light |
| Vitamin B1 | Beriberi | Weakness, nerve damage |
| Vitamin C | Scurvy | Bleeding gums, weakness |
| Vitamin D | Rickets | Soft, deformed bones |
| Vitamin K | Poor blood clotting | Excessive bleeding |
| Iron | Anaemia | Pale skin, fatigue |
| Iodine | Goiter | Swollen neck |
Nutrition in Plants
Autotrophic Nutrition
- Plants produce their own food via photosynthesis
- Raw materials: CO₂ (from air), H₂O (from soil), sunlight
- Site: Leaves (broad, thin, green — maximum surface area for light absorption)
Heterotrophic Plants
Some plants cannot produce their own food:
- Insectivorous plants: Pitcher plant, Venus flytrap — digest insects to get nitrogen
- Parasitic plants: Cuscuta (dodder) — has no chlorophyll, absorbs food from host plant
- Saprophytic plants: Indian pipe (Monotropa) — grows on decaying matter
Mineral Nutrition in Plants
Plants need macronutrients (required in larger quantities):
- N: Chlorophyll synthesis, leaf growth
- P: Root development, flowering
- K: Water regulation, disease resistance
- Ca: Cell wall formation
- Mg: Central atom in chlorophyll
- S: Protein synthesis
And micronutrients (required in small quantities): Iron (chlorophyll synthesis), Manganese, Zinc, Boron, Copper, Chlorine, Molybdenum.
Fertilizers: NPK fertilizers are the most common — Nitrogen (N), Phosphorus (P), Potassium (K). Urea, DAP (Diammonium phosphate), Potash are commonly used.
CTET Exam Focus
- Photosynthesis: Overall equation, light reaction (photolysis), Calvin cycle (dark reaction)
- Chlorophyll: Role, structure (porphyrin head + phytol tail)
- Human digestive system: Mouth → esophagus → stomach → small intestine → large intestine
- Bile: Emulsification of fats, not digestion
- Pancreatic enzymes: Trypsin, amylase, lipase
- Intestinal enzymes: Maltase, sucrase, lactase
- Deficiency diseases: Night blindness (Vit A), Rickets (Vit D), Scurvy (Vit C), Anaemia (Iron), Goiter (Iodine)
- Insectivorous plants: Pitcher plant, Venus flytrap
- NPK fertilizers: Main macronutrients for plants
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