Nutrition in Living Organisms

1. Modes of Nutrition

Nutrition is the process by which living organisms obtain and utilize food for growth, repair, and maintenance. There are two primary modes:

• Autotrophic Nutrition: Organisms (autotrophs) manufacture their own food from simple inorganic substances. This includes Photosynthesis (using sunlight, e.g., green plants, algae) and Chemosynthesis (using chemical energy, e.g., Nitrosomonas).
• Heterotrophic Nutrition: Organisms (heterotrophs) depend on already manufactured food from plants or animals.

2. Types of Heterotrophic Nutrition

• Holozoic: Ingestion of solid organic food (e.g., Man, Sheep, Amoeba).
• Parasitic: Living on or in another organism (host) to obtain food, often causing harm (e.g., Tapeworm, Roundworm, and Loranthus - a plant parasite).
• Saprophytic: Feeding on dead and decaying organic matter (e.g., Rhizopus, Mushrooms).
• Carnivorous Plants: Plants that grow in nitrogen-deficient soil and trap insects to supplement nitrogen (e.g., Sundew, Bladderwort, Venus Flytrap).

3. Plant Nutrition

Photosynthesis

The process of converting CO2 and water into glucose using sunlight trapped by chlorophyll. It occurs in two stages:

• Light Stage (Light-dependent): Occurs in the grana of chloroplasts. Light energy splits water (Photolysis) into Hydrogen ions and Oxygen.
• Dark Stage (Light-independent): Occurs in the stroma. Carbon (IV) oxide is reduced to glucose using the Hydrogen and ATP from the light stage.

Conditions for Photosynthesis: Chlorophyll, sunlight, CO2, and water. The presence of starch (detected by Iodine turning blue-black) is evidence that photosynthesis has occurred.

Mineral Requirements

• Macro-nutrients: Required in large amounts (N, P, K, Mg, Ca, S).
• Micro-nutrients: Required in trace amounts (Fe, Zn, Cu, Bo).
• Deficiency Symptoms: Nitrogen (stunted growth, yellow leaves/chlorosis), Phosphorus (purple leaves, poor root growth), Potassium (yellowing leaf margins, premature death).

4. Animal Nutrition

Classes of Food

• Carbohydrates: Energy source (e.g., Rice, Yam).
• Proteins: Growth and repair (e.g., Beans, Meat). Deficiency leads to Kwashiorkor.
• Fats and Oils: Energy storage and insulation.
• Vitamins: Organic compounds for health. Vit C (Scurvy), Vit D (Rickets), Vit A (Night blindness).
• Mineral Salts: Calcium (bones/teeth), Iron (hemoglobin).

Food Tests

• Starch: Iodine solution (Blue-black color).
• Reducing Sugar: Benedict's solution + Heat (Brick-red precipitate).
• Protein: Biuret test (Violet/Purple color) or Millon's reagent (Brick-red precipitate).
• Fats: Translucent spot on paper or Sudan III (Red stain).

5. The Mammalian Tooth

Structure includes the Crown (visible part), Root (buried in the socket), Enamel (hardest part), Dentine, and Pulp cavity (contains nerves and blood vessels).

Types and Dental Formulae

• Incisors: Cutting and biting.
• Canines: Tearing flesh.
• Premolars/Molars: Grinding and chewing.
• Formulae:
  • Man: I 2/2, C 1/1, PM 2/2, M 3/3 = 32
  • Sheep (Herbivore): I 0/3, C 0/1, PM 3/3, M 3/3 = 32 (Note the diastema - gap between front and back teeth).
  • Dog (Carnivore): I 3/3, C 1/1, PM 4/4, M 2/3 = 42.

6. Digestion and Enzymes

Digestion is the breakdown of large, insoluble food molecules into small, soluble, absorbable forms. The process involves: Ingestion → Digestion → Absorption → Assimilation → Egestion.

Digestive Enzymes

• Mouth: Salivary amylase (Ptyalin) breaks starch to maltose.
• Stomach: Pepsin (Proteins to Peptones), Renin (curdles milk).
• Pancreas (secreted into duodenum): Trypsin (Proteins to Peptides), Amylopsin (Starch to Maltose), Steapsin (Fats to Fatty acids/Glycerol).
• Small Intestine: Maltase (Maltose to Glucose), Peptidase (Polypeptides to Amino acids).