Cell Structure

• Making temporary slides and drawing cells correctly.
• Magnification = image size ÷ actual size, with mm, µm and nm.
• Calibrating an eyepiece graticule with a stage micrometer.
• Resolution versus magnification in light and electron microscopes.
• Structure and function of 15 eukaryotic cell structures; plant versus animal cells.
• Cells use ATP from respiration for energy-requiring processes.
• Prokaryotic cells compared with eukaryotic cells; viruses as non-cellular structures.

Temporary preparations and biological drawings

Making a temporary slide

1. Peel a single layer of cells (e.g. the inner epidermis of an onion bulb leaf) or scrape cheek cells with a clean cotton bud.
2. Place the material flat in a drop of water or stain on a clean slide: iodine solution for plant cells (stains starch and nuclei), methylene blue for animal cells (stains nuclei).
3. Lower a coverslip at an angle with a mounted needle so that air bubbles are not trapped. Blot away excess liquid.
4. Focus with the low-power objective first, then switch to higher power.

Drawing cells from slides and photomicrographs

• Sharp HB pencil; clear, continuous, single lines; no shading, no colour.
• Draw large (use most of the space) and keep the proportions of the specimen.
• Draw only what you can see. For plant cells, show the cell wall as two lines and draw only a few cells.
• Label lines drawn with a ruler, ending exactly on the structure, not crossing, no arrowheads; labels outside the drawing.

Magnification and actual size

Magnification is how many times larger the image is than the actual object. Measure the image in mm, then convert so both lengths are in the same unit.

Eyepiece graticule and stage micrometer

eyepiece graticule calibrated stage micrometer

1. Line up the graticule scale with the stage micrometer scale.
2. Find a point where lines on both scales coincide and count the divisions on each.