Gas Exchange

• Diusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration.
• Molecules move down a concentration gradient, as a result of their random movement.
• Diusion across the cell membrane is the process by which gas exchange occurs.
• Single-celled organisms, such as amoeba, can exchange gases sufficiently by simple diusion through the cell membrane.
• Gas exchange in multicellular organisms, such as plants and animals, occurs through organ systems that maximise the exchange of materials.
• Gills are the gas exchange organs in fish, lungs in humans and leaves or roots in plants.
• Gas exchange organs increase the efficiency of exchange in a number of ways: having a large surface area to increase the rate of transport, a short diffusion distance for substances to move across, and being well ventilated to maintain steep concentration gradients.
• In this investigation, your evaluation should look something like this: Change - We will change whether the student has exercised or not.
• We will repeat the investigation several times to ensure our results are reliable.
• When working with practical investigations, remember to consider your CORMS evaluation.
• Breathing rate can vary substantially and changes quickly after exercise finishes.
• Running at a certain speed on a treadmill or cycling with a specific power output on a watt bike is an example of exercise.
• Allow significant rest breaks in between exercises and ensure that periods of exercise are not prolonged.
• The best way to measure breathing rate is to begin counting as soon as the time interval begins and only measure for 15s, then multiply up to calculate breaths per minute.
• Students may become more fatigued throughout the duration of the investigation, especially with repeats.
• The students should be of the same age, gender, size and general fitness.
• The processes of respiration and photosynthesis both rely on the exchange of oxygen and carbon dioxide.
• When we need to increase the rate of gas exchange, the internal intercostal muscles work to pull the ribs down and in to decrease the volume of the thorax more, forcing air out more forcefully and quickly, this is called forced exhalation.
• There is a greater need to rid the body of increased levels of carbon dioxide produced during strenuous activity, allowing a greater volume of gases to be exchanged.
• The terms inhalation and inspiration mean the same thing, both refer to breathing in.
• The alveoli are highly specialised for gas exchange, with many rounded alveolar sacs giving a very large surface area to volume ratio.
• Alveoli and the capillaries around them have thin, single layers of cells to minimise diffusion distance.
• A layer of moisture on the surface of the alveoli helps diffusion as gases dissolve.
• Alveoli are specifically adapted to maximise gas exchange.
• The sequence of events during breathing in and out involves the external and internal intercostal muscles, the rib cage, the diaphragm, the volume and the pressure-volume of the lungs.
• The terms exhalation and expiration mean the same thing, both refer to breathing out.
• Ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space.
• A good blood supply ensures a constant supply of blood high in carbon dioxide and low in oxygen.
• During respiration, all living cells require the uptake of oxygen and the release of carbon dioxide.
• Give students an exercise type where intensity is easier to control, such as walking or swimming.
• The effect of exercise on breathing can be investigated using a stopwatch, two students, and a method involving counting breaths for 15 seconds and multiplying by 4.
• Student A should exercise for a set time (at least 4 minutes) and immediately after exercising, count the breaths taken in 15 seconds and multiply by 4 to obtain the breathing rate per minute.
• It is difficult to control all variables in relation to the students being tested, such as fitness and food consumption prior to the exercise.
• Student A's breathing rate at rest should be worked out using the method.
• To ensure students are similar in size, general fitness, age, gender, and provide each with the same meal before exercise.
• The result of the exercise should be compared to the breathing rate at rest in order to work out the change in breathing rate as a result of exercise.
• An unfit individual may have a higher breathing rate while resting, a more rapid increase in breathing rate during exercise, and a longer recovery period for their breathing rate to return back to a normal resting rate.
• The breathing rate during and after exercise is affected by fitness levels.
• The intensity of exercise can be controlled more easily for each reading.
• Exercise causes the frequency of breathing to increase in order to provide more oxygen for respiration and to pay off any subsequent oxygen debt.