A student is making a slide of algal cells in a drop of pond water. She rests one edge of a cover slip on the slide beside the drop, supports the cover slip at about 45° with a mounted needle and then lowers it slowly.
Why does she lower the cover slip in this way?
to push the air out so that no bubbles are trapped over the cells
to draw off the extra water from around the edge of the cover slip
to let the water evaporate so that the cells stick to the slide
to press the algal cells together into a thick, easily seen layer
130 exam-style questions on OCR GCSE Biology 1.1 Cell structures, covering 1.1.1 Viewing cells with light microscopes, 1.1.2 Sub-cellular structures and functions, and 1.1.3 Electron microscopy and resolution. Each one has a worked solution and a mark scheme showing where the marks go.