Animal Physiology — Nutrition and Digestion — Practice

Question 1

Name the type of nutrition in: (a) mushroom (b) Cuscuta (c) humans (d) green plants.

Accepted Answer

Step 1 — Apply definitions.
  (a) Mushroom: SAPROPHYTIC — absorbs from dead organic matter.
  (b) Cuscuta: PARASITIC — lives on and derives nutrients from a host plant.
  (c) Humans: HOLOZOIC — ingest solid food, digest internally.
  (d) Green plants: AUTOTROPHIC — make food by photosynthesis.

✦ Answer: Saprophytic, Parasitic, Holozoic, Autotrophic.

Question 2

Name the enzyme found in saliva. What is its substrate and product? At what pH does it work?

Accepted Answer

Step 1 — Identify the enzyme.
  Salivary Amylase (also called ptyalin) is found in saliva.

Step 2 — Substrate and product.
  Substrate: Starch (a polysaccharide).
  Product: Maltose (a disaccharide).

Step 3 — Optimal pH.
  pH ~7 (neutral) — matches the neutral/slightly alkaline pH of saliva.

✦ Answer: Salivary amylase · starch → maltose · pH ~7.

Question 3

What is bile? Where is it produced and where is it stored? What is its role in digestion?

Accepted Answer

Step 1 — What is bile.
  Bile is a greenish-yellow alkaline fluid produced by the LIVER.

Step 2 — Storage.
  Bile is stored in the GALL BLADDER and released into the small intestine (duodenum) when fat is present.

Step 3 — Role.
  Bile does NOT contain digestive enzymes. Its role is EMULSIFICATION OF FATS — it breaks large fat globules into tiny fat droplets, increasing surface area for lipase action.

✦ Answer: Produced by liver, stored in gall bladder. Emulsifies fat — NO enzymes.

Question 4

Describe the role of the stomach and small intestine in human digestion. Name the enzymes and secretions involved in each.

Accepted Answer

Step 1 — STOMACH:
  J-shaped muscular organ. Gastric glands secrete gastric juice containing:
  • HCl (pH ~2) — kills bacteria, activates pepsinogen to pepsin.
  • Pepsin — protease: proteins → peptides.
  • Mucus — protects stomach lining from acid and pepsin.
  Food churned into semi-liquid CHYME (stays ~3-4 hours).

Step 2 — SMALL INTESTINE (6-7 m: duodenum, jejunum, ileum):
  Three digestive juices act here:
  (a) Bile (from liver/gall bladder) — emulsifies fat (no enzymes).
  (b) Pancreatic juice — trypsin (proteins → peptides), lipase (fats → FA + glycerol), amylase (starch → maltose).
  (c) Intestinal juice — maltase (maltose → glucose), peptidases (peptides → amino acids).
  VILLI provide surface area. Blood absorbs glucose + amino acids. Lacteals absorb fatty acids + glycerol.

✦ Answer: Stomach = HCl + pepsin + mucus → chyme. Small intestine = bile + pancreatic juice + intestinal juice → complete digestion + absorption via villi.

Question 5

Draw a table listing five digestive enzymes with their source, site of action, substrate, product, and optimal pH.

Accepted Answer

Step 1 — Set up the table.

Enzyme | Source | Site | Substrate → Product | pH
  -------|--------|------|---------------------|----
  Salivary Amylase | Salivary glands | Mouth | Starch → Maltose | ~7
  Pepsin | Gastric glands | Stomach | Proteins → Peptides | ~2
  Trypsin | Pancreas | Small intestine | Proteins → Peptides | ~8
  Lipase | Pancreas | Small intestine | Fats → FA + Glycerol | ~8
  Maltase | Intestinal glands | Small intestine | Maltose → Glucose | ~7.5

Step 2 — Key fact to add.
  BILE is NOT an enzyme — it EMULSIFIES fat (physical). Source: Liver. Stored in: Gall bladder.

✦ Answer: Table as above. Remember: bile ≠ enzyme.

Question 6

Describe the complete human digestive system, naming all organs, the secretions at each stage, and how food is finally absorbed. Include deficiency diseases caused by nutritional deficiency.

Accepted Answer

Step 1 — INGESTION: Food enters the MOUTH. Teeth mechanically break food. Salivary amylase begins starch digestion (starch → maltose). Bolus formed and swallowed.

Step 2 — OESOPHAGUS: 25 cm muscular tube. PERISTALSIS (wave-like contractions) moves food downward.

Step 3 — STOMACH: HCl activates pepsin. Pepsin: proteins → peptides. Mucus protects lining. Food becomes CHYME (3-4 hours).

Step 4 — SMALL INTESTINE (COMPLETE DIGESTION):
  Bile: emulsifies fat. Trypsin: proteins → peptides. Lipase: fats → fatty acids + glycerol. Amylase: starch → maltose. Maltase: maltose → glucose. Peptidases: peptides → amino acids.
  ABSORPTION via VILLI: blood takes glucose + amino acids. Lacteals take fatty acids + glycerol.

Step 5 — LARGE INTESTINE: Absorbs water + minerals. E. coli bacteria produce vitamins B and K. Faeces formed.

Step 6 — EGESTION: Faeces expelled through rectum and anus.

Step 7 — DEFICIENCY DISEASES:
  Protein deficiency → Kwashiorkor (swollen belly). Protein + calorie deficiency → Marasmus. Iron deficiency → Anaemia (low Hb). Vitamin A → Night blindness. Vitamin C → Scurvy. Vitamin D → Rickets.

✦ Answer: Complete sequence with all enzymes, secretions, and deficiency diseases as above.

Practice — Animal Physiology — Nutrition and Digestion

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