04-BS-13 · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2013 — 04-BS-13, Biology. Three-hour, closed-book exam (one double-sided aid sheet permitted, approved Casio/Sharp calculator allowed). Format: Part I offers 6 questions (any 3 constitute a complete answer, 20 marks each) and Part II offers 4 questions (any 2 constitute a complete answer, 20 marks each) — a full paper is 5 questions. All 10 are solved below for completeness. Most questions require an essay-format answer; Q1–Q4 are calculation questions.
Reference texts: Shuler & Kargi, Bioprocess Engineering: Basic Concepts (2nd ed., Prentice Hall) — elemental/electron balances, yield coefficients, fermenter energy balances; Madigan et al., Brock Biology of Microorganisms (15th ed., Pearson) — bacterial/viral/fungal morphology and physiology; Toledo, Fundamentals of Food Process Engineering (3rd ed., Springer) — plant/animal tissue structure, rheology, water activity.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Plant and animal materials are organized hierarchically — cell → tissue → organ → whole organism — and each level of this hierarchy imposes a distinct constraint on how the material can be mechanically handled or processed.
Size-reduction behaviour is set at the cellular/tissue level: the characteristic fracture length scale (roughly the cell or fibre dimension) governs whether size reduction proceeds by brittle fracture (turgid parenchyma, most fruits/vegetables — energy input scales with new surface area created, Rittinger's law regime) or requires ductile cutting/shredding (fibrous, lignified tissue, meat muscle — energy input scales more with the new volume/length processed, closer to a Bond/Kick's-law regime).
Anisotropic (fibrous) organization — wood and stalk grain, muscle fibre direction in meat, vascular bundle orientation in root vegetables — dictates a strongly preferred cutting direction: cutting across the grain in meat gives tender, short-fibre pieces and much lower shear force than cutting with the grain, and the same principle governs splinter-free peeling and slicing of fibrous vegetables.
Porosity/intercellular organization controls fluid and heat transport during processing: the higher void fraction of loosely packed parenchyma (e.g. apple) permits faster vacuum impregnation, brine/sugar infusion, and drying than denser tissue (e.g. potato), because the effective diffusivity for both liquid penetration and moisture removal scales with the connected pore volume.
Compound (multi-tissue) organization — skin over flesh over core/seed in fruit; hide/skin over fat over muscle over bone in an animal carcass — is exploited directly by separation unit operations: the mechanical property mismatch between adjacent tissue types (tough skin vs. soft flesh, tendon vs. muscle) is what makes mechanical peeling (abrasion, lye, or steam peeling) and deboning/trimming operations possible as clean, controllable steps rather than uniform destructive processing.
