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.
(a) Virus shapes and characteristics. Viruses occur in several characteristic morphologies: icosahedral (a near-spherical, 20-triangular-face geometric capsid — e.g. adenovirus, poliovirus), helical (a rod-like protein coat wound around a helical nucleic acid core — e.g. tobacco mosaic virus, rabies virus), enveloped forms (an icosahedral or helical capsid wrapped in a lipid envelope derived from the host cell membrane, studded with viral glycoproteins — e.g. influenza, HIV), and complex forms (a head-and-tail structure, characteristic of many bacteriophages). Main characteristics: viruses are obligate intracellular parasites with no independent metabolism and cannot replicate outside a living host cell; they are sub-microscopic (roughly 20–300 nm, well below the resolution of a light microscope); they possess either DNA or RNA as genetic material, never both; they are acellular, lacking ribosomes, cytoplasm and organelles; and they replicate by redirecting the host cell's own biosynthetic machinery, via lytic (immediate replication and cell lysis) or lysogenic (genome integration and latency) cycles.
(b) Distinguishing fungal characteristics. Fungi are eukaryotic (unlike bacteria), with cell walls built of chitin (unlike the cellulose walls of plants); they are heterotrophic by absorption — secreting extracellular digestive enzymes and absorbing the resulting small molecules — rather than by ingestion (animals) or photosynthesis (plants); most are multicellular and filamentous, forming branching hyphae that aggregate into a mycelium, though yeasts are unicellular; they reproduce via both sexual and asexual spores; and vegetative fungal cells are non-motile (no flagella), unlike many bacteria and protozoa.
Beneficial uses in food. Yeasts (Saccharomyces) drive bread leavening and alcoholic fermentation (beer, wine); filamentous fungi produce antibiotics (Penicillium → penicillin) and are used directly in food fermentations (Aspergillus for soy sauce and citric acid production; Penicillium roqueforti/camemberti for cheese ripening); fungi are cultivated directly as food (mushrooms) and are exploited industrially as sources of enzymes (amylases, proteases) and single-cell protein.
Harmful roles in food. Visible mould growth causes direct spoilage and quality loss; several moulds (notably Aspergillus flavus) produce potent mycotoxins such as aflatoxins (carcinogenic) — a food-safety hazard that can be present even without visible mould growth or obvious spoilage; other mycotoxins (ochratoxins, patulin) pose similar risks; fungal spores can also be allergenic, and fungal metabolic byproducts frequently cause off-flavours and off-odours in contaminated products.
