Health, disease and the development of medicines study guide

Plant disease detection requires systematic steps both in the field and in the laboratory. Initial fieldwork involves looking for visible symptoms such as leaf discoloration, spots, wilting, or abnormal growth. Investigators then rule out possible environmental or abiotic causes like drought, poor nutrition, or physical damage. Analysis of the pattern of affected plants helps: a uniform pattern suggests environmental factors, while patchy or clustered symptoms suggest an infectious agent. For definitive diagnosis, sample collection follows, and laboratory methods such as microscopy (to see pathogens directly), culturing (to grow and identify microbes), and molecular techniques like DNA-based tests are used to identify the specific causative organism.

When investigating how antiseptics, antibiotics, or plant extracts affect microbial cultures, use standard aseptic techniques (disinfecting work areas, wearing gloves and goggles, using sterilised tools) and only permitted, non-pathogenic bacterial species. The independent variable is the type or concentration of antimicrobial agent, and the dependent variable is the zone of inhibition (clear area around the disc) on an agar plate. Control all possible variables, such as the same bacterial strain, agar depth and composition, incubation time, and disc size and placement. Carefully inoculate plates, add antimicrobial discs and a control, seal plates with tape, and label clearly. Incubate plates upside down at or below 25°C for safety. After incubation, do not open the plate – measure the inhibition zone diameter through the closed lid using a ruler. For graphical presentation: display antimicrobial type or concentration on the x-axis and mean zone diameter on the y-axis as a bar graph or line graph. Evaluate the reliability by repeating the experiment, calculating averages, and comparing data; assess uncertainty by comparing the ruler precision (for example, ±1 mm) to the measured zone, then calculate percentage error as (uncertainty/mean) × 100%. Dispose of all cultures and materials by sterilisation (e.g., autoclave) under supervision. Never incubate plates above 25°C or open plates after incubation in schools.