Unit 32: Medicine, Agriculture and Industry — Short Questions

The therapeutic window is the range of plasma drug concentrations (between the Minimum Effective Concentration, MEC, and the Minimum Toxic Concentration, MTC) that are effective without being harmful — the drug's "sweet spot." Its significance is that it tells doctors the actual concentration range within which a dose must be kept: a wide window gives flexibility in dosing, while a narrow window means the effective and toxic doses are close together, requiring careful, monitored dosing (therapeutic drug monitoring). The Therapeutic Index (TI = TD₅₀/ED₅₀) differs in that it is a single quantitative ratio comparing the toxic dose to the effective dose across a population (each causing an effect in 50% of people) — it is a safety score used to compare drugs, whereas the therapeutic window is the actual concentration range used clinically to keep an individual patient's dose safe and effective.

Penicillin's structure closely resembles the amino acid sequence of the natural substrate of transpeptidase, the enzyme that cross-links (strengthens) the bacterial cell wall. The enzyme mistakenly binds penicillin in place of its real substrate. Because penicillin's four-membered beta-lactam ring is highly strained, it opens upon binding and forms a permanent covalent bond with the active site of transpeptidase, inactivating the enzyme irreversibly. Without functional transpeptidase, the bacterial cell wall cannot be properly cross-linked, so the bacteria keep growing without a strong wall and eventually burst and die.

Opiates bind to opioid receptors (mainly Mu receptors) in the brain and spinal cord, mimicking the body's natural endorphins (a key-and-lock mechanism). This binding closes calcium channels and opens potassium channels in the neuron, hyperpolarizing it so that it becomes much harder for the cell to transmit the pain signal onward, thereby blocking pain signals from reaching the brain. Opiates also trigger excess dopamine release in the brain's reward centre, producing a sense of relief and well-being.

Bacteria are independent, living organisms with their own distinct cellular machinery (e.g., cell walls), so drugs like penicillin can target bacteria-specific structures without harming human cells. Viruses, however, are not independently alive — they live inside host cells and hijack the host's own DNA/RNA machinery to replicate, so it is hard to design a drug that kills the virus without damaging healthy human cells. Viruses also mutate very quickly, so a drug effective one year may fail the next (this is why flu vaccines are updated yearly), and viruses can integrate into the host genome and stay dormant for years, which current antivirals cannot reach since they act only on actively replicating viruses.

A pest population naturally contains some genetic variation, including a few individuals that happen to be less susceptible to a given pesticide. When the pesticide is applied, susceptible pests are killed while the resistant individuals survive and reproduce, passing their resistance genes to their offspring — this is natural selection acting on the population. With repeated application of the same pesticide over many generations, the proportion of resistant individuals increases until the pesticide becomes largely ineffective, forcing farmers to use higher doses or more toxic pesticides, which can cause further environmental and health harm.

This is the Chlor-Alkali process — an industrial electrolysis method that breaks down sodium chloride brine to produce chlorine (Cl₂), sodium hydroxide/caustic soda (NaOH), and hydrogen (H₂), commonly using modern membrane cell technology for high efficiency and purity.

Plastics — made from cracked crude oil molecules, used daily in packaging, containers, and household items. Synthetic rubber — also derived from petrochemical cracking, used in making tyres and footwear.

Therapeutic Index (TI) is a quantitative measure of a drug's safety; it compares the dose that causes a toxic effect in 50% of people (TD₅₀) to the dose that produces the desired effect in 50% of people (ED₅₀): TI = TD₅₀ / ED₅₀. For Drug A: TI = TD₅₀/ED₅₀ = 80 mg / 20 mg = 4.

The therapeutic window is the range of drug concentrations/doses that are effective without causing harmful side effects, bounded by the minimum effective concentration/dose (MEC) and the minimum toxic concentration/dose (MTC). For Drug B, the window spans from MEC = 5 mg/L to MTC = 50 mg/dm³, a width of 45 (mg/L). For Drug C, the window spans from the effective dose of 10 mg to the toxic dose of 15 mg, a width of only 5 mg. Drug B has the wider therapeutic window, because the gap between its effective and toxic levels (45) is much larger than Drug C's gap (5), giving doctors much more flexibility in dosing Drug B safely.

Drug A has TI = TD₅₀/ED₅₀ = 80/20 = 4. Drug C's therapeutic index, found the same way (toxic dose/effective dose), is 15/10 = 1.5. Since Drug A's TI (4) is higher than Drug C's TI (1.5), Drug A is the safer drug — it has a larger relative gap between its effective and toxic doses. Drug C, with a TI close to 1 and a narrow 5 mg window, is comparatively less safe and would need very careful, closely monitored dosing.

Synthetic fertilizers are man-made through chemical processes, such as the Haber-Bosch process used to produce ammonia (NH₃). Organic fertilizers, in contrast, come from natural sources such as compost or animal manure, rather than being manufactured chemically.

Nitrogen (N) a fundamental component of amino acids (which build proteins) and of chlorophyll, the pigment needed for photosynthesis; it is usually the most limiting factor in crop production. Phosphorus (P): a structural component of ATP (adenosine triphosphate), which stores and releases energy for the plant. Potassium (K): does not become part of the plant's physical structure but acts as an osmoregulator and activates over sixty different enzymes that facilitate plant metabolism.