Scaling up Study Guide

A potometer is a device used to measure the rate of water uptake by a plant shoot. It is important to understand that a potometer actually measures water uptake, not directly transpiration, although water uptake is largely driven by transpiration. The apparatus consists of a plant shoot inserted into a rubber bung, which then fits into a tube containing water. The end of this tube dips into a beaker of water or is connected to a capillary tube with a trapped air bubble. As the plant transpires, water is lost from its leaves, creating a transpiration pull that draws water up through the stem. This movement of water is what the potometer measures. If using a capillary tube with an air bubble, the distance the air bubble moves along a scale over a set period indicates the rate of water uptake. Factors such as temperature, humidity, light intensity, and wind speed can affect the rate of transpiration, and consequently, the rate of water uptake. To investigate a specific factor, all other factors must be kept constant. For example, to study the effect of temperature, the potometer could be placed in different temperature environments while light, humidity, and air movement are kept the same. The apparatus must be assembled carefully underwater to avoid trapping air bubbles in the xylem vessels of the cut shoot, which could block water flow. If the air bubble reaches the end of the capillary tube, it can be reset by opening a tap or moving a syringe plunger to return the bubble to the start. The rate is then calculated by dividing the distance moved by the time taken.

The human circulatory system, also known as the cardiovascular system, is a vital organ system that ensures the transportation of essential substances throughout the body. It is a double circulatory system, meaning blood passes through the heart twice for each complete circuit of the body. This efficiency allows for effective delivery of oxygen and nutrients and removal of carbon dioxide and waste products, crucial for maintaining life in large, active organisms. The system is comprised of the heart, blood vessels (arteries, veins, capillaries), and blood. The heart acts as a muscular pump, propelling blood through a vast network of vessels. Arteries carry oxygenated blood away from the heart to the body's tissues (except for the pulmonary artery, which carries deoxygenated blood to the lungs). Veins return deoxygenated blood from the body's tissues back to the heart (except for the pulmonary vein, which carries oxygenated blood from the lungs). Capillaries are extremely narrow vessels that form networks within tissues, facilitating the exchange of gases, nutrients, and waste products between blood and body cells. The two main circuits are the pulmonary circuit, which carries blood between the heart and the lungs for gas exchange, and the systemic circuit, which carries blood between the heart and the rest of the body. This separation ensures that oxygenated and deoxygenated blood do not mix, maximising oxygen delivery to the body's cells.