Substances larger than which of the following are normally not allowed to pass through the filtration membrane?

• A. albumin molecules
• B. glucose molecules
• C. water molecules
• D. sodium ions

Answer: (A)

Verified step by step guidance

1. Understand the concept of filtration membranes in microbiology, which typically allow the passage of small molecules while blocking larger ones based on size exclusion.
2. Identify the size range of the molecules listed: sodium ions, water molecules, glucose molecules, and albumin molecules, noting that albumin is a large protein compared to the others.
3. Recall that filtration membranes used in microbiology (such as those with pore sizes around 0.2 micrometers) allow small molecules like water, sodium ions, and glucose to pass through but block larger molecules like proteins.
4. Recognize that albumin molecules are significantly larger than glucose, water, and sodium ions, and thus are normally not allowed to pass through the filtration membrane.
5. Conclude that substances larger than albumin molecules are typically blocked by the filtration membrane, making albumin the cutoff point for passage.