1.1 The Microscope in Cell Studies

A temporary preparation lets fresh cellular material be viewed with a light microscope without making a permanent slide.

1. Put a liquid sample on a clean slide, or cut a solid specimen thin enough for light to pass through.
2. Add a suitable stain when contrast is needed.
3. Lower the coverslip from one edge to reduce trapped air bubbles.
4. Remove excess liquid and view the preparation promptly so it stays in place and does not dry out.

The coverslip protects the objective lens and limits drying. Iodine can increase contrast in plant tissue, while methylene blue can make cheek-cell structures easier to distinguish.

A stain improves contrast but does not create detail that the microscope cannot resolve. The preparation must remain thin and representative of the material being investigated.

A biological drawing is a large, accurate line record of the structures that can actually be seen in a microscope slide or photomicrograph—not a reconstruction of the textbook cell.

1. Inspect the image first and decide which structures are genuinely visible.
2. Set the drawing size and relative proportions from the image; include a title and magnification or scale bar when supplied.
3. Draw the observed outline and internal features with clear, single lines and no shading.
4. Label only visible structures with straight, separate label lines that point precisely to the feature.

A cell drawing records individual cells and their internal features, usually at higher magnification. A plan drawing records the distribution of tissues at lower magnification, so it should not invent cell-level detail.

Neatness cannot justify an unseen organelle. If a feature is not resolved in the image, leaving it out is more accurate than drawing the expected textbook version.

Magnification is the ratio of image size to actual size: it tells how many times larger the image is than the specimen.

1. Identify the unknown quantity: magnification (M), image size (I) or actual size (A).
2. Rearrange the relationship if needed.
3. Convert image and actual sizes into the same unit before dividing or multiplying.
4. Substitute, calculate, then report the size with its unit and a sensible precision.
5. Sense-check: a magnified image should be larger than the actual specimen.

A 1 µm bacterium viewed at ×50 000 forms an image equivalent to 50 000 µm, or 50 mm. The unit conversion is part of the calculation, not an optional presentation step.

Magnification has no unit; image size and actual size do. Do not compare or combine lengths until their units match, and do not treat higher magnification as proof of higher resolution.

An eyepiece graticule is an arbitrary scale in the microscope view. A stage micrometer calibrates how much real distance one graticule division represents at the current magnification.

1. Superimpose the graticule and stage-micrometer scales.
2. Choose a matching interval and record its real stage-micrometer distance.
3. Divide that real distance by the number of graticule divisions to obtain the factor.
4. Count specimen divisions and multiply by the factor.
5. Recalibrate whenever the objective or magnification changes.

If 20 graticule divisions coincide with 0.20 mm on the stage micrometer, one division is 0.010 mm = 10 µm. A chloroplast spanning 4 divisions is therefore 40 µm at that setting.

The eyepiece scale is not automatically in micrometres and is not calibrated by magnification alone. The same number of divisions can represent a different length after the objective is changed.

Resolution is the smallest separation at which two points can still be distinguished as separate. Magnification makes an image larger; resolution determines whether that enlargement reveals new detail.

• Light microscope: visible light has a longer wavelength, so closely spaced structures have a coarser resolution limit.
• Electron microscope: electrons have a much shorter effective wavelength, so finer ultrastructure can be resolved.

Cristae in a mitochondrion may be present in an image but appear merged under a light microscope. Higher magnification alone would enlarge the blur; higher resolution is what separates the membranes.

A larger image is not automatically a more informative image. State magnification and resolution separately when explaining why an electron microscope is needed.