Practical skills Study Guide

Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution). This process is crucial for plant cells, which have partially permeable cell membranes. To investigate osmosis in biological samples like potato cylinders, you can place them in sugar solutions of varying concentrations. The water potential of the solution outside the cells determines the direction of water movement. If the external solution has a higher water potential (is more dilute) than the cell sap, water will move into the potato cells, causing them to swell and gain mass or lengthen. If the external solution has a lower water potential (is more concentrated), water will move out of the potato cells, causing them to shrink and lose mass or shorten. If the external solution has the same water potential as the cell sap, there will be no net movement of water, and the potato tissue's mass or length will remain relatively unchanged. By accurately measuring the initial and final mass or length of the potato cylinders, and comparing these changes across different sugar concentrations, we can understand the effects of water potential on biological tissues and even estimate the water potential of the potato cells themselves.

Microscopes are essential tools in biology, allowing us to observe living organisms and prepared slides that are too small to be seen with the naked eye. A light microscope works by passing light through a specimen and then through two lenses: the objective lens and the eyepiece lens. The magnification of the microscope is calculated by multiplying the magnification of the eyepiece lens by the magnification of the objective lens. For example, if the eyepiece is 10x and the objective is 40x, the total magnification is 400x. When using a microscope, it's crucial to handle it safely, place slides correctly, and focus carefully using both coarse and fine adjustment knobs. Producing labelled scientific drawings of observations is a key skill. These drawings should be large, clear, include all visible details, use continuous lines (no shading or sketching), and have clear, uncrossed label lines pointing to specific features. Measurements of observable structures can be taken using a graticule (a scale in the eyepiece) that has been calibrated with a stage micrometer. This allows for accurate calculation of the actual size of features from their magnified image size. Safety precautions include handling glass slides and cover slips carefully to avoid cuts, and ensuring the microscope is stable to prevent it from falling.