Health, disease and the development of medicines study guide

Infectious diseases are caused by pathogens such as bacteria, viruses, fungi, and protists, which can be transmitted between organisms. Understanding these diseases involves knowing the pathogen responsible, the symptoms they cause, and the specific body parts affected. For instance, cholera, caused by bacteria, leads to severe diarrhoea due to bacterial toxins affecting the small intestine. Tuberculosis, also bacterial, primarily damages the lungs, forming lesions and often causing a persistent cough. Chalara ash dieback, a fungal disease, impacts ash trees, causing leaf loss and bark lesions that can eventually kill the tree. Malaria, caused by a protist transmitted by mosquitoes, targets red blood cells and liver cells, leading to cycles of fever and chills. HIV, a viral infection, specifically attacks and destroys white blood cells, weakening the immune system over time and eventually leading to Acquired Immunodeficiency Syndrome (AIDS), where the body can no longer fight off opportunistic infections. Helicobacter pylori bacteria can cause stomach ulcers by damaging the protective lining of the stomach. Ebola, a severe viral disease, causes haemorrhagic fever, characterised by high fever, severe bleeding, and organ failure, often with a high mortality rate.

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.