04-BS-13 · December 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 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 and Q7 are calculation questions.
Reference texts: Shuler & Kargi, Bioprocess Engineering: Basic Concepts (2nd ed., Prentice Hall) — elemental/electron balances, yield coefficients, fermenter energy balances, growth kinetics; Madigan et al., Brock Biology of Microorganisms (15th ed., Pearson) — bacterial/viral morphology, physiology and growth control; Toledo, Fundamentals of Food Process Engineering (3rd ed., Springer) — plant/animal tissue structure.
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.
The gross (tissue-level) organization of a plant or animal product — how cells are shaped, bonded to their neighbours, and arranged into protective, conductive and ground/parenchymal tissue systems — sets the mechanical and transport behaviour that every downstream processing operation must work with or against.
Protective tissues. Plant epidermis/periderm (cutin- or suberin-coated) and animal skin/hide (keratinized epidermis over collagenous dermis) are the primary barrier to moisture loss and microbial ingress. Processing example: peeling operations (lye, steam, mechanical abrasion) are designed specifically to remove this tough, low-permeability layer without damaging the softer tissue beneath, because leaving it intact would block drying, brining or heat penetration in later steps.
Vascular/connective tissues. Plant xylem/phloem (lignified, longitudinally aligned) and animal tendon/connective tissue (collagen fibre bundles) impose strong mechanical anisotropy. Processing example: meat is always cut across the muscle-fibre grain to shorten fibre length and improve tenderness, and celery or asparagus is peeled/de-stringed to remove the fibrous vascular strands that would otherwise be perceived as toughness; the same anisotropy dictates the preferred splitting direction for wood and fibrous root vegetables.
Ground/parenchymal tissue. Thin-walled, turgor-pressurized parenchyma (fruit/vegetable flesh) or loose areolar/adipose tissue (animal) dominates bulk texture and water content. Processing example: high-porosity parenchyma (apple) permits rapid vacuum impregnation, osmotic dehydration and freeze–drying because its large intercellular void fraction gives high effective diffusivity, whereas dense, low-porosity tissue (potato tuber) processes far more slowly under the same conditions and needs longer blanching or drying times.
Compound (multi-tissue) organization. Real products are composites — skin over flesh over core/seed in fruit, or hide over fat over muscle over bone in a carcass. Processing example: the sharp mechanical-property mismatch between adjacent tissue types (tough skin vs. soft flesh; tendon vs. muscle) is exactly what mechanical separation operations (peeling, deboning, trimming) exploit to achieve a clean, controllable cut rather than uniformly destroying the whole product.
