6.9 Osmotic pressure of a cell In Section 6.2 .3, we derived...

6.9 Osmotic pressure of a cell In Section $6.2 .3,$ we derived the van't Hoff formula for the osmotic pressure and performed an estimate of the osmotic pressure experienced by a bacterium as a result of its impermeability to inorganic ions. Examine the contribution to the osmotic pressure of a bacterium coming from the presence of proteins within the cell. How does this compare with the contribution to the osmotic pressure from inorganic ions described in the section? See Table 2.1 and Figure 2.4 for the relevant data.

6.9 Osmotic pressure of a cell
In Section $6.2 .3,$ we derived the van't Hoff formula for the osmotic pressure and performed an estimate of the osmotic pressure experienced by a bacterium as a result of its impermeability to inorganic ions. Examine the contribution to the osmotic pressure of a bacterium coming from the presence of proteins within the cell.
How does this compare with the contribution to the osmotic pressure from inorganic ions described in the section? See Table 2.1 and Figure 2.4 for the relevant data.

Key Concepts

Comparative Contribution of Macromolecules and Inorganic Ions

In biological cells, while large molecules such as proteins are impermeable and can contribute to osmotic pressure, their impact is typically less significant than that of inorganic ions because the concentrations of proteins are much lower. Inorganic ions usually dominate the osmotic balance within cells, and their higher molarity results in a larger contribution to the overall osmotic pressure.

Membrane Permeability

The concept of permeability is central to osmosis. Only solutes that are impermeable to the cell membrane contribute to an osmotic pressure gradient. In cells, both inorganic ions (if they are not allowed to freely cross the membrane) and larger molecules like proteins can create differences in concentration that drive water movement.

Role of Solute Concentration in Osmotic Pressure

The magnitude of osmotic pressure is directly linked to the concentration of solute particles. In a cell, inorganic ions are often present in higher molar concentrations compared to proteins, meaning that even if proteins are impermeable, their contribution to the overall osmotic pressure can be lower than that of inorganic ions due to their relatively lower numbers.

Van't Hoff Law

This law provides the relationship between osmotic pressure and solute concentration in dilute solutions. It states that osmotic pressure is proportional to the molar concentration of solute particles, the temperature, and the gas constant. This fundamental formula is used to estimate the pressure that a solute generates when separated by a semipermeable membrane.

Colligative Properties

Osmotic pressure is a colligative property, meaning it depends primarily on the number of solute particles rather than their identity. This is important in biological systems where differing solutes, such as inorganic ions and proteins, can influence the net osmotic pressure based solely on their concentration and ability to cross membranes.

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