Practical skills Study Guide

Microorganisms like bacteria are all around us, and some can cause infections. Antimicrobial treatments are substances that can kill or inhibit the growth of these microorganisms. These include antibiotics (which target bacteria) and antiseptics/disinfectants (which can kill a broader range of microbes on surfaces or living tissue). Investigating their effectiveness often involves growing a bacterial culture and exposing it to different antimicrobial agents. A common method is the agar diffusion technique, where bacteria are spread evenly across an agar plate to form a 'lawn'. Small discs, each soaked in a different antimicrobial treatment, are then placed on the agar. As the antimicrobial diffuses into the agar, it may create a 'zone of inhibition' around the disc, where bacterial growth is prevented. The size of this clear zone indicates the effectiveness of the treatment: a larger zone suggests a more potent antimicrobial. Proper aseptic techniques are crucial to prevent contamination from unwanted microorganisms and to ensure the safety of the experimenter. This involves sterilising equipment (like inoculating loops and petri dishes), working near a Bunsen flame to create an upward current that prevents airborne microbes from settling, and correctly disposing of bacterial cultures. Temperature control is also important, as bacteria grow optimally within a specific range, usually around 25°C for school experiments to minimise the growth of human pathogens.

Our bodies respond to exercise by increasing the rate of various physiological processes to meet the higher demand for energy. When we engage in physical activity, our muscles work harder, requiring more oxygen for aerobic respiration and producing more carbon dioxide as a waste product. To supply this increased oxygen and remove carbon dioxide efficiently, the cardiovascular and respiratory systems adjust.

The heart rate, or pulse rate, increases to pump blood faster around the body. This delivers oxygen and nutrients to working muscles and carries away carbon dioxide and other waste products more quickly. Pulse rate can be measured by counting heartbeats at specific points like the radial artery (wrist) or carotid artery (neck) over a set period, typically 15 seconds, and then multiplying to get beats per minute.

Similarly, the ventilation rate (breathing rate) also increases. This means we breathe more frequently and often more deeply, increasing the amount of air exchanged with each breath. The purpose is to take in more oxygen and expel more carbon dioxide from the lungs. Ventilation rate can be measured by counting breaths over a set period, usually 30 seconds or 1 minute.

Investigating these responses involves measuring baseline rates (before exercise), rates during exercise, and rates during recovery (after exercise). A typical investigation might involve light exercise such as stepping up and down from a low bench for a few minutes. Safety precautions are essential, such as ensuring participants are fit for exercise and stopping if they feel unwell. Key variables to control include the type and intensity of exercise, the duration of exercise, and the environmental temperature. The independent variable is the exercise level (before, during, after), and the dependent variables are pulse rate and ventilation rate. Data collected can be plotted on a graph, typically a line graph, to visualise the changes over time.