A Level Biology Practice Exam

What is meant by contrast in microscopy?

1. Making all cell components visible without staining

2. Staining specific cell components to enhance visibility

3. Using multiple types of light to increase image brightness

4. Improving magnification without altering the sample

The correct answer is: Staining specific cell components to enhance visibility

Contrast in microscopy refers to the difference in light intensity between the specimen and its background or between different parts of the specimen itself. By staining specific cell components, the contrast is enhanced, making these structures more distinguishable from surrounding areas. Stains absorb different wavelengths of light, allowing certain structures to become more prominent against the lighter background. This process is essential for examining and identifying cellular structures that might otherwise be difficult to observe due to their similar refractive indices with the surrounding medium. The other aspects mentioned involve different microscopy techniques. Making all cell components visible without staining does not enhance contrast; rather, it relies on natural differences in refractive index, which might not provide clarity. Using multiple types of light can help with image brightness but does not directly pertain to the concept of contrast. Improving magnification without altering the sample focuses on the overall enlargement of the image rather than distinguishing features within it. Thus, the correct answer accurately captures the essence of how contrast is achieved in microscopy.