04-BS-13 · December 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — December 2016 — 04-BS-13, Biology. Three-hour, closed-book exam (one double-sided aid sheet permitted, approved calculator allowed). Format: Part I offers 5 questions (any 3 constitute a complete answer, 20 marks each) and Part II offers 3 questions (any 2 constitute a complete answer, 20 marks each) — a full paper is 5 questions. All 8 numbered questions are solved below for completeness. Q2–Q5 and Q7 are calculation/derivation questions; Q1, Q6, and Q8 are essay questions.
Reference texts: Shuler & Kargi, Bioprocess Engineering: Basic Concepts (2nd ed., Prentice Hall) — elemental/electron balances, yield coefficients, fermenter mass and energy balances, growth kinetics; Madigan et al., Brock Biology of Microorganisms (15th ed., Pearson) — bacterial/eukaryotic cell structure, fungi, protozoa/algae, Gram-stain cell envelope; Toledo, Fundamentals of Food Process Engineering (3rd ed., Springer) — plant tissue structure and cereal grain morphology.
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) Prokaryotes vs. eukaryotes. Prokaryotic cells (bacteria, archaea) lack a membrane-bound nucleus — their DNA is a single circular chromosome condensed into a nucleoid region directly exposed to the cytoplasm — and have no membrane-bound organelles (no mitochondria, ER, Golgi, chloroplasts); ribosomes are the smaller 70S type, and cell size is typically 1–5 µm. Eukaryotic cells (fungi, protozoa, algae, plants, animals) have a true membrane-bound nucleus, an extensive internal membrane system (endoplasmic reticulum, Golgi apparatus) compartmentalising metabolic functions, membrane-bound organelles (mitochondria for respiration; chloroplasts in photosynthetic lineages), larger 80S ribosomes, and are generally larger (10–100 µm). Functionally, this compartmentalisation lets eukaryotes separate and regulate processes (e.g. transcription in the nucleus vs. translation in the cytoplasm) that occur together in the prokaryotic cytoplasm.
(b) Major classes of fungi. Fungi are traditionally divided into four classes based on their sexual reproductive structures and hyphal septation: Zygomycetes (e.g. Rhizopus bread mould) — coenocytic (non-septate, multinucleate) hyphae, sexual spores are thick-walled zygospores; Ascomycetes (e.g. Saccharomyces, Aspergillus, Penicillium) — septate hyphae, sexual ascospores produced in a sac-like ascus, includes both yeasts and moulds; Basidiomycetes (mushrooms, rusts, smuts) — septate hyphae, sexual basidiospores borne externally on a club-shaped basidium; Deuteromycetes ("Fungi Imperfecti", e.g. many industrially important moulds) — septate hyphae, no known sexual stage has been observed, classified provisionally by asexual (conidial) reproduction alone. The classes therefore differ mainly in hyphal septation and in the structure that bears their sexual spores.
(c) Protozoa vs. algae. Both are typically unicellular eukaryotic microorganisms, but differ fundamentally in nutrition and cell covering. Protozoa are non-photosynthetic (heterotrophic), lack a rigid cell wall (bounded only by a flexible pellicle or plasma membrane, permitting shape change and phagocytic feeding), and move by cilia, flagella, or amoeboid pseudopodia; they possess a contractile vacuole for osmoregulation in freshwater species. Algae are photosynthetic (autotrophic), possess chloroplasts containing chlorophyll (and often accessory pigments giving characteristic colours — e.g. brown, red algae), and most have a rigid cell wall (commonly cellulose-based, sometimes silica in diatoms). Functionally, protozoa occupy consumer/predator niches (grazing on bacteria, other protozoa, organic particles) while algae are primary producers, fixing CO2 via photosynthesis at the base of aquatic food webs.
(d) Gram-negative vs. Gram-positive cell envelope. Both bacterial groups have a plasma membrane and a peptidoglycan (murein) layer providing shape and osmotic protection, but the arrangement differs substantially:
Gram-positive bacteria have a single plasma membrane surrounded by a thick (multi-layered) peptidoglycan wall with teichoic acid polymers threaded through it (contributing negative surface charge and, in part, retention of the crystal-violet/iodine complex during Gram staining). Gram-negative bacteria have a thin peptidoglycan layer confined to a periplasmic space between the plasma membrane and a second, outer membrane whose outer leaflet is lipopolysaccharide (LPS) — the endotoxic component responsible for much of Gram-negative pathogenicity; they have no teichoic acid. This structural difference is exactly what the Gram stain detects: the thick Gram-positive wall traps the crystal-violet–iodine complex against alcohol decolourisation, while the thin Gram-negative wall (and disrupted outer membrane) does not.
