Opacity

Definition

Opacity is the measure of how impenetrable a substance is to light. In microbiology, it refers to the ability of cells or substances to obstruct the passage of light, hindering visibility under a microscope.

5 Must Know Facts For Your Next Test

1. Opaque substances do not allow light to pass through them, making them appear dark or completely black under a microscope.
2. Opacity can be used to determine the density and concentration of microbial cultures; higher opacity often indicates higher cell density.
3. Microbial colonies with high opacity can make it difficult for scientists to observe internal structures without additional staining techniques.
4. The degree of opacity in microbial samples can affect the accuracy of light-based quantitative assays, such as spectrophotometry.
5. Different wavelengths of light may interact differently with opaque substances, affecting their apparent opacity.

Review Questions

• How does opacity affect the visibility of microbial cells under a microscope?
• Why might increased opacity indicate a higher cell density in microbial cultures?
• What challenges do highly opaque microbial samples present for scientific observation?

Related terms

Translucency: The property that allows some light to pass through but scatters it, creating a blurred image.

Transparency: A property where almost all incident light passes through with minimal scattering, providing clear visibility.

Spectrophotometry: A technique used to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam passes through sample solution.