04-BS-13 · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exam — May 2019, 04-BS-13, Biology. Three-hour, closed-book exam (one double-sided aid sheet permitted, approved Casio/Sharp calculator allowed). Format: Part I lists six 20-mark questions (Q1–Q6), and the instruction requires 3 of the 6, one from each pair (1&2), (3&4), (5&6); Part II lists three 20-mark questions (Q7–Q9), any 2 of 3. Together this matches the notice page's "FIVE questions constitute a complete exam" (3 + 2 = 5). All nine questions are solved below for completeness. Q4's stoichiometric equation (page 2) and its lettered sub-parts (page 3, "Given the following parameters for cell growth…") are one continuous question split across a page break not two separate questions; they are combined here. The source's page-3/4 footer reads "May 2018" against page-1/2's clear "May 2019" header. Q3, Q4, Q5, Q6, and Q9 are calculation/derivation questions; Q1, Q2, Q7, and Q8 are essay/qualitative questions.
Reference texts: Shuler & Kargi, Bioprocess Engineering: Basic Concepts (2nd ed., Prentice Hall) — elemental/electron balances, yield coefficients, maintenance (Pirt/Luedeking–Piret) corrections, respiratory quotient, fermenter energy balances; Madigan et al., Brock Biology of Microorganisms (15th ed., Pearson) — bacterial morphology, prokaryote/eukaryote comparison, viruses, fungi, diauxic growth and the lac operon; Toledo, Fundamentals of Food Process Engineering (3rd ed., Springer) — water activity and sorption.
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) Three basic bacterial shapes. Cocci (spherical or near-spherical cells, which may occur singly, in pairs (diplococci), chains (streptococci), or clusters (staphylococci)); bacilli (rod-shaped cells, varying from short/plump to long/thin, occurring singly or in chains); and spirilla/spira (helical or curved/comma-shaped cells — vibrio (comma-shaped), spirillum (rigid helix), and spirochete (flexible helix) are common sub-forms).
Similarities between prokaryotic and eukaryotic cells. Both are bounded by a phospholipid-bilayer plasma membrane that regulates transport and maintains the internal chemical environment; both use DNA as the hereditary material and the same essential genetic code and central dogma (DNA → RNA → protein) with ribosomes as the site of translation; both carry out the same fundamental metabolic strategies (glycolysis-type substrate breakdown, ATP as the universal energy currency); and both maintain cytoplasm as the site of most biochemical reactions.
Differences between prokaryotic and eukaryotic cells.
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | No true nucleus — DNA in a nucleoid region, not membrane-bound | True membrane-bound nucleus |
| Genome organization | Single circular chromosome (usually), often with plasmids | Multiple linear chromosomes, histone-packaged, in the nucleus |
| Membrane-bound organelles | Absent (no mitochondria, ER, Golgi, chloroplasts) | Present (mitochondria, ER, Golgi, and chloroplasts in plants/algae) |
| Ribosomes | 70S (30S+50S subunits) | 80S (40S+60S subunits); 70S in mitochondria/chloroplasts |
| Cell size | Typically 1–10 µm | Typically 10–100 µm |
| Cell division | Binary fission | Mitosis (and meiosis for gametes) |
| Cytoskeleton | Simple, limited (e.g. FtsZ, MreB homologs) | Complex (microtubules, microfilaments, intermediate filaments) |
(b) Main characteristics of viruses. Viruses are obligate intracellular parasites — they have no independent metabolism and cannot reproduce outside a host cell. Each virion consists of a nucleic acid genome (DNA or RNA, never both, single- or double-stranded) enclosed in a protein coat (capsid) built from repeating protein subunits (capsomeres); some viruses additionally carry a lipid envelope derived from host membrane, studded with viral glycoproteins. Viruses are typically far smaller than cells (roughly 20–300 nm) and are acellular — they have no cytoplasm, ribosomes, or membrane-bound metabolism of their own, instead hijacking the host cell's ribosomes, energy supply, and biosynthetic machinery to replicate. They exhibit strict host and often tissue/cell-type specificity, mediated by specific receptor recognition at the cell surface, and each type infects only a narrow host range.
Essay/qualitative question — no numerical data in the source; content follows standard microbiology treatment (Madigan et al., Brock Biology of Microorganisms, Ch. 2–3, 8).
