# Calculating Magnification in Microscopy

• The level of magnification provided by a microscope is calculated by multiplying the magnification of the objective lens by the magnification of the eyepiece lens.
• The total magnification is expressed as a multiplication factor, such as “200x”, meaning the image is magnified 200 times larger than its actual size.
• The objective lens is the one nearest the object under observation. Eyepiece lens is the one through which the observer looks at the object.

# Measuring the Size of Cells and Organelles

• To measure cells and their organelles, a graticule is needed. A graticule is a miniature ruler which fits into the eyepiece.
• Graticules are graduated in an arbitrary unit and the scale needs to be calibrated for each objective lens.
• Calibration is achieved using a stage micrometer, a slide with a precise scale, typically marked in 0.1mm divisions.
• The size of cells or cell structures are then calculated using the formula: actual size = image size ÷ magnification.

# Estimating Sizes of Cells and Organelles from Drawings or Images

• To estimate sizes of cells from drawings or images, it helps to have a reference scale that denotes an actual measurement in the image.
• Remember the image is magnified, so estimating requires considering the level of magnification.
• As an example, if the image is labelled with a measurement scale of 100nm (nanometres), under a magnification of 2000x, you can estimate the size of a cell or an organelle within the scale in the image.

# Relevance in Biological Science

• Understanding magnification and size of cells and organelles allows us to understand the relative scales of these structures, and how they interact within the living organism.
• Understanding how to calculate and estimate sizes under varying magnifications is a critical skill in biological microscopy, which allows us to observe cells and organelles and discover their functions.

Remember, accurate measuring and estimation play an important role in many biological research and experiment analyses.