It's not accurate to say cells can't be smaller than 0.1 µm. While most cells are larger than that, there are exceptions, and the limit is more about the minimum requirements for life, rather than a hard and fast rule. Here's why:

1. Surface Area to Volume Ratio:

* Smaller cells have a higher surface area to volume ratio. This is advantageous for nutrient uptake and waste removal, as these processes occur across the cell membrane.

* However, as a cell gets smaller, the relative volume decreases, making it harder to house all the necessary components for life. These components include DNA, ribosomes, enzymes, and other essential molecules.

2. Essential Components:

* A cell needs a certain minimum volume to fit the basic machinery of life. For instance, the DNA molecule, responsible for carrying genetic information, is relatively large and requires space.

* Smaller cells would struggle to accommodate these essential structures and carry out their functions effectively.

3. Mycoplasma:

* The smallest known free-living cells are Mycoplasma, with a diameter of around 0.1 µm. They are highly specialized bacteria that lack a cell wall, which contributes to their small size. However, even Mycoplasma have a surprisingly complex internal structure.

4. Viruses:

* Viruses are much smaller than cells, with some being less than 0.1 µm. However, viruses are not considered living organisms because they lack the ability to reproduce independently and rely on host cells for their functions.

In conclusion:

The lower limit for cell size is not fixed. While there are fundamental constraints related to the minimum requirements for life, cells can be incredibly small, as demonstrated by Mycoplasma. However, being too small poses challenges for housing essential components and maintaining necessary functions.