You already know more than you think. This section helps you surface prior knowledge, identify gaps, and build curiosity before the new content arrives.
Before reading anything new — write freely. There are no wrong answers here. This is about making your thinking visible, not performing.
Rate each concept before we start. Return here at the end to see how your confidence has changed.
Answer from memory — even partial answers count. This is low-stakes retrieval, not a test.
Bacteria reproduce by a process called binary fission — they simply split in half. In ideal conditions, some bacteria can divide every 20 minutes. This exponential growth rate is why infections can escalate with alarming speed.
Press + to simulate each 20-minute division. 2ⁿ cells after n divisions.
For bacteria to grow rapidly, all of the following conditions must be met. This is also key to understanding how we control bacterial growth — by removing one condition.
Carbon, nitrogen and energy source for metabolism. Agar jelly provides all the nutrients bacteria need to grow in culture.
Solvent for biochemical reactions and transport of substances in and out of cells. Most bacteria cannot grow in dry conditions.
Enzymes work optimally at higher temps. Most pathogens grow best near 37°C (body temp). Cold slows growth; excess heat denatures enzymes.
Aerobic bacteria need O₂ for aerobic respiration. Removes this and growth slows significantly. Anaerobic bacteria grow without O₂.
Bacterial enzymes denature outside their optimal pH range. Most bacteria prefer near-neutral pH (6.5–7.5). Extreme pH inhibits growth.
This student's answer contains 3 errors. Click the underlined phrases to reveal each mistake.
To investigate bacteria — including testing whether plant extracts can kill them — we need to culture them: grow large numbers in controlled conditions so they can be observed and measured. Bacteria are most commonly grown on agar plates, where the jelly provides all required nutrients at the correct pH.
Without looking back, write the 6 key steps in the correct order. Focus on the reason for each step, not just what to do.
Plants can provide an ideal warm, nutrient-rich environment for bacteria and fungi. This is a serious threat — microorganisms can damage and even destroy them. In response, many plants have evolved chemical defences to kill or inhibit any microbes that invade. These include both antiseptic compounds and antibiotic-like chemicals.
The antimicrobial properties of plant extracts can be investigated in the laboratory using the disc diffusion method on agar culture plates.
A larger zone of inhibition = a more potent antimicrobial chemical in the extract.
A student tested three plant extracts (A, B, C) and measured the zone of inhibition for each.
| Plant Extract | Zone of Inhibition (mm) |
|---|---|
| Extract A (cotton plant) | 18 |
| Extract B (lavender) | 7 |
| Extract C (distilled water — control) | 0 |
When investigating antimicrobial plant extracts, which of the following steps require aseptic technique? Click each item, then drag it to the correct zone.
Plants produce compounds beyond antimicrobials — some have effects ranging from pain relief to anti-cancer activity. The challenge scientists face is: how do you reliably extract, purify, dose and reproduce these effects from something as variable as a living plant?
Quinine, derived from the bark of the cinchona tree, is used to prevent and treat malaria — a life-threatening disease spread by mosquitoes, common in many tropical areas. However, its use enabled loggers and developers to work in the Amazon Basin, raising a profound ethical tension:
The concentration of any active chemical in a plant varies significantly — making precise dosing from raw plant material unreliable and potentially dangerous:
| Variable | Effect on chemical concentration | Clinical risk of raw extract |
|---|---|---|
| Age of plant | Younger / older plants produce more or less of a compound | Inconsistent dose — could be too low (no effect) or too high (toxic) |
| Season | Chemical production varies with seasonal growth cycles | Seasonal availability; potency changes across months |
| Time of day | Metabolic activity changes throughout the day | Harvesting time affects chemical yield |
| Plant part used | Active chemical may concentrate in bark, roots, leaves etc. | Using wrong part yields little or no therapeutic effect |
Scientists isolate the active compound, analyse its structure, and then synthesise it industrially. In many cases the molecule is also chemically modified — as with salicylic acid → aspirin — to improve its safety or efficacy.
These questions pull from all five sections. No notes — test your memory first.
Write a definition for each term from memory. Then reveal the correct definition.
Look back at your Think-Puzzle-Explore notes from Section 1. What has genuinely changed in your understanding? This is not about listing facts — it is about tracking intellectual change.
Re-rate the same three concepts from Section 1. Has your confidence shifted?