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Heterotrophic Nutrition and Digestion – Long Answer Questions

Medium Level (Application & Explanation)

Q1. Differentiate between saprophytic, parasitic, and holozoic (ingestive) modes of heterotrophic nutrition with suitable examples. Explain how body structures support each mode.

Answer:

  • In saprophytic nutrition, organisms like fungi (mushrooms, bread moulds) secrete digestive enzymes outside the body to break down dead organic matter and then absorb the dissolved nutrients. Their hyphae provide a large surface area to release enzymes and absorb food efficiently.
  • In parasitic nutrition, organisms such as Cuscuta (dodder) or leeches take nutrients from a living host without killing it. Parasites have specialized structures like haustoria (in plants) or suckers (in leeches) to attach and extract nutrients.
  • In holozoic nutrition, animals like humans, cows, and lions ingest food, digest it internally, absorb the nutrients, and egest waste. Their teeth, alimentary canal, and enzymes are adapted for mechanical and chemical digestion. These structural adaptations match their ecological roles—herbivores for plant matter and carnivores for animal tissue.

Q2. Describe how Amoeba and Paramecium obtain nutrition. Compare their adaptations for ingestion, digestion, and egestion.

Answer:

  • Amoeba uses pseudopodia (temporary finger-like extensions) to engulf food (phagocytosis). A food vacuole forms where enzymes digest the food. The nutrients are absorbed (assimilation) into the cytoplasm, and undigested residue is expelled at the cell surface by exocytosis.
  • Paramecium has cilia that beat in a coordinated manner to sweep food and water into the oral groove and then to the gullet where food vacuoles form. Digestion occurs inside the food vacuole with the help of enzymes. Wastes are expelled through a specialized area called the cytoproct.
  • Comparison: Amoeba relies on shape change and is flexible in food capture, suitable for varied prey. Paramecium uses structured feeding through cilia and an oral groove for directed intake. Both use intracellular digestion but differ in how food is captured and how egestion is organized.

Q3. Explain how the structure of the human alimentary canal enables efficient digestion and absorption of food.

Answer:

  • The mouth has teeth for mechanical breakdown and saliva with salivary amylase to start digestion of starch. The tongue helps in mixing food into a bolus for swallowing.
  • The oesophagus uses peristalsis (wave-like muscle movements) to push food into the stomach.
  • The stomach secretes hydrochloric acid (HCl) to kill microbes and provide an acidic pH for pepsin to begin protein digestion; mucus protects the stomach lining.
  • The small intestine is the major site for digestion and absorption. Bile from the liver emulsifies fats; pancreatic enzymes (amylase, trypsin, lipase) and intestinal enzymes complete digestion. Villi and microvilli greatly increase surface area, enabling rapid absorption into blood and lymph (lacteals).
  • The large intestine absorbs H₂O and salts, compacts waste, and forms feces for egestion via the rectum and anus. Specialization at each step ensures maximal efficiency.

Q4. Using the “saliva and starch” activity, explain the role of saliva in digestion. Identify the control, variables, observations, and conclusion.

Answer:

  • In this activity, test tube A receives starch + saliva, while test tube B (control) has starch only. After 20–30 minutes, iodine solution is added to both.
  • Control: Test tube B (shows the natural blue‑black color with starch).
  • Independent variable: Presence of saliva; dependent variable: Color change with iodine; constants: Volume and concentration of starch, time, temperature, amount of iodine.
  • Observation: Tube A shows no blue‑black color or a lighter shade (starch reduced), whereas Tube B remains blue‑black (starch present).
  • Conclusion: Salivary amylase in saliva chemically breaks down starch into simpler sugars (like maltose), so iodine does not turn blue‑black. The experiment demonstrates that digestion begins in the mouth and highlights the importance of enzymes and maintaining appropriate time and temperature for enzyme action.

Q5. What is dental caries? Explain how plaque forms and suggest effective methods to prevent tooth decay.

Answer:

  • Dental caries is the decay of tooth enamel and dentine caused by bacterial action on sugars in food. Bacteria form a sticky film called plaque by binding to food residues and tooth surfaces.
  • When we eat sugary or starchy foods, plaque bacteria ferment sugars to acids (e.g., lactic acid), lowering pH. This causes demineralization of enamel. Frequent snacking increases acid attack frequency, while thick plaque blocks saliva, reducing its ability to neutralize acids and aid remineralization.
  • Prevention:
    • Brush twice daily with fluoride toothpaste; floss to remove plaque between teeth.
    • Limit sugary snacks and sticky foods; prefer fiber-rich foods; drink water.
    • Rinse mouth after meals; use xylitol gum to stimulate saliva.
    • Regular dental check-ups and professional cleaning.
    • Maintain good saliva flow (avoid dry mouth), as saliva buffers acids and supplies minerals.

High Complexity (Analytical & Scenario-Based)

Q6. A cow and a lion obtain food very differently. Analyse how their nutrition strategy relates to their teeth and digestive tract, and how this affects energy extraction.

Answer:

  • The cow (herbivore) grazes on cellulose-rich grasses. It has broad, flat molars for grinding and a longer intestinal tract to allow more time for digestion and absorption. Many herbivores host microbes that help break down cellulose, increasing energy extraction from plants. Multiple stomach chambers or a large caecum assist fermentation and nutrient uptake.
  • The lion (carnivore) hunts animals and consumes protein- and fat-rich meat. It has sharp canines and cutting premolars for tearing flesh and a shorter intestine because proteins and fats are easier to digest chemically. Powerful gastric secretions help rapidly denature proteins.
  • Thus, feeding strategy, dentition, gut length, and enzymes/microbes are coordinated. Herbivores invest in mechanical grinding and long retention time; carnivores in rapid protein digestion, each maximizing energy from their specific diet.

Q7. A student with very low saliva production eats a high-starch meal. Predict what happens to digestion in the mouth and later in the gut. Suggest coping strategies.

Answer:

  • With low saliva, there is poor bolus formation, making swallowing harder, and little salivary amylase to start starch digestion. The starch remains largely undigested in the mouth, and there is reduced lubrication and weakened buffering, increasing risk of dental caries.
  • In the small intestine, pancreatic amylase will compensate by breaking starch into maltose, and intestinal enzymes will form glucose for absorption, so overall energy yield is still adequate, though initial digestion is delayed.
  • Coping strategies:
    • Sip water with meals; eat soft, moist foods; take smaller bites and chew well.
    • Stimulate saliva with sugar-free (xylitol) gum; consider saliva substitutes if advised.
    • Maintain strict oral hygiene (fluoride toothpaste, flossing) and limit sugary snacks to reduce caries risk.
    • Seek medical advice to address causes of xerostomia and protect oral health.

Q8. If the villi of the small intestine are damaged, what changes occur in digestion and health? Explain by linking structure to function.

Answer:

  • Villi and microvilli increase the surface area for nutrient absorption and contain capillaries (for amino acids, glucose) and lacteals (for fats). Damage to villi (e.g., in certain intestinal disorders) drastically reduces surface area, causing malabsorption.
  • Consequences include:
    • Weight loss, fatigue, and poor growth due to inadequate nutrient uptake.
    • Diarrhea or bulky, fatty stools (steatorrhea) from unabsorbed fats.
    • Micronutrient deficiencies (iron → anemia; calcium → weak bones; vitamins → multiple symptoms).
    • Bloating and gas due to unabsorbed food fermenting in the gut.
  • The digestive enzymes may still act, but without intact villi, absorption into blood and lymph is inefficient. Restoring villi health and diet modification are essential to regain efficient absorption and overall wellbeing.

Q9. Design a fair test to compare how temperature or pH affects salivary amylase activity on starch. State hypothesis, variables, method, and error control.

Answer:

  • Hypothesis: Salivary amylase works best near 37°C and pH ~7; activity decreases at very low/high temperatures or pH.
  • Variables:
    • Independent: Temperature (e.g., 10°C, 25°C, 37°C, 60°C) or pH (5, 7, 9).
    • Dependent: Time taken for iodine‑starch color to disappear (or reducing sugars formed).
    • Controlled: Starch concentration/volume, saliva volume, incubation time, mixing, iodine amount.
  • Method:
    • Prepare equal starch solutions in multiple tubes; add equal saliva to each.
    • Incubate at set temperatures or pH (use buffers for pH).
    • At intervals, test drops with iodine; record time until no blue‑black color.
  • Error control:
    • Keep timing precise, use water baths for stable temperature, same pipettes, and repeat trials. Interpret results to find the optimum and understand enzyme denaturation at ext...

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