Unit IV — Aves & Mammals: Exam Answers (2, 5, 12 marks)
1) (2‑mark) — Orders adapted for flight and digging
- Flight: Order Chiroptera — example: Pteropus (fruit bat).
- Digging: Order Eulipotyphla (formerly Insectivora) — example: Talpa (mole).
Quick exam tip: Give the order name plus one correct example — that secures the full 2 marks.
2) (5‑mark) — Double mode of respiration in Aves
Intro (1 line): Birds possess a highly efficient respiratory system in which a single breath results in airflow through the lungs during two cycles of inspiration–expiration — called double (two‑cycle) respiration.
Key anatomy
- Trachea and syrinx
- Lungs (small, rigid — with parabronchi)
- Posterior air sacs (receive fresh air)
- Anterior air sacs (receive used air before exhalation)
Mechanism — four steps
- First inspiration: Fresh air enters the trachea; most flows into the posterior air sacs (and some into the lungs).
- First expiration: Air from posterior sacs is forced through lungs (parabronchi) — gas exchange occurs.
- Second inspiration: Air that passed through lungs moves into anterior air sacs. Simultaneously, new fresh air fills posterior sacs.
- Second expiration: Air from anterior sacs is expelled out through the trachea.
Key feature: Unidirectional airflow through parabronchi (posterior → lungs → anterior → out), so gas exchange occurs during both inhalation and exhalation — giving continuous, high‑efficiency O₂ uptake.
Physiological significance: Supports high metabolic demand of flight.
Marking guide (5 marks): Anatomy named (1) • Steps/mechanism clearly described (3) • Significance + neat diagram (1).
3) (12‑mark) — Digestive system of a ruminant (with diagram) + comparison
Intro: Ruminants (cow, sheep, goat) are herbivorous mammals with a four‑compartment stomach where microbial fermentation occurs before enzymatic digestion.
A. Structure & function — Ruminant digestive system
Major parts: Mouth → Oesophagus → Stomach (Rumen → Reticulum → Omasum → Abomasum) → Small intestine (duodenum, jejunum, ileum) → Large intestine (caecum, colon) → Rectum → Anus.
Stomach compartments (details)
- Rumen — large fermentation chamber. Microbes ferment cellulose to volatile fatty acids (VFAs) absorbed for energy. Produces gas (eructation required).
- Reticulum — honeycomb mucosa; traps heavy particles; helps form cud for rumination.
- Omasum — many folds (manyplies); reduces particle size, absorbs water & minerals.
- Abomasum — true glandular stomach; secretes HCl & pepsin; enzymatic digestion of proteins (including microbial protein).
Process summary: Ingestion → rumen (fermentation) → regurgitation & rumination → reticulum/omasum processing → abomasum enzymatic digestion → small intestine absorption → large intestine & excretion.
Comparison: Ruminant vs Non‑ruminant (use in answer)
| Feature | Ruminant (Cow) | Non‑Ruminant (Pig/Human) |
|---|---|---|
| Stomach chambers | Four: rumen, reticulum, omasum, abomasum | Single glandular stomach |
| Primary digestion site | Foregut fermentation (rumen) | Enzymatic digestion in stomach & small intestine |
| Microbial role | Extensive microbial fermentation; microbial protein synthesis | Limited foregut microbes; some hindgut fermentation |
| Feeding habit | Adapted to high‑fiber diets; rumination | Omnivore/carnivore diets; faster throughput |
| Stomach pH | Rumen near neutral; abomasum acidic | Stomach acidic (pepsin/HCl) |
Marking guide (12 marks)
Physiological significance: Microbial fermentation allows utilization of cellulose → VFAs supply energy; microbial protein digested in abomasum supplies amino acids. Rumen function sensitive to sudden diet changes (risk: acidosis).
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