Which tests assess cell death caused by a material by measuring cell number or growth before and after exposure to that material?

• A. Cytotoxicity Tests
• B. Mechanical testing
• C. Thermal analysis
• D. Optical density assay

Answer: (A)

When assessing whether a material harms cells, the important idea is cytotoxicity: does exposure to the material reduce how many cells survive or how well they grow? In cytotoxicity tests, cells are exposed to the material (or its extract) and then viability is measured after exposure. If the cell number or growth rate drops compared with unexposed controls, the material is considered cytotoxic. This approach directly links a material’s presence to its effect on cellular health.

Common ways to measure this include assessing metabolic activity with colorimetric or fluorometric assays (for example, tests where living cells convert a substrate into a product that can be quantified by optical density or fluorescence), or directly counting viable cells and using membrane integrity stains. The key point is the before-and-after comparison of cell viability to determine if the material causes cell death or inhibits growth.

In contrast, mechanical testing looks at physical properties like strength and elasticity, which tell you about performance, not biological response. Thermal analysis examines how a material behaves with temperature changes. An optical density reading by itself is simply a measurement method used within viability assays, not a standalone category of tests for cell death caused by a material.