Problem 1 - Biology: How Life Works

Question

Given a selectively permeable membrane that is permeable to water but not to a particular solute and given that there are different solute concentrations on the two sides of the membrane, show the direction of water movement and label the side with the higher osmotic pressure.

Step-by-Step Solution

Answer

Water moves towards the higher solute concentration, which also has higher osmotic pressure.

Step 1: Understand the Concept of Osmosis

Osmosis is the movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration, until equilibrium is reached. It occurs to balance solute concentrations on both sides of the membrane.

Step 2: Identify Solute Concentrations

Determine which side of the membrane has a higher solute concentration and which side has a lower solute concentration. This is important as water moves from low to high solute concentration.

Step 3: Determine Water Movement

Since the membrane is permeable to water, water molecules will move towards the side with the higher solute concentration. This movement continues until the concentrations become equal or reach an osmotic balance.

Step 4: Label the Higher Osmotic Pressure

The side with the higher solute concentration has higher osmotic pressure because it tends to "pull" water towards itself to dilute the solutes. Label this side as having higher osmotic pressure.

Key Concepts

Selectively Permeable Membrane

In biology, membranes play a crucial role in maintaining homeostasis within cells. A selectively permeable membrane is special because it allows some substances to pass through while blocking others.
This type of membrane is permeable to water molecules but not to all solute particles.
This selectivity ensures that cells can control what enters and exits, maintaining a stable internal environment.

• Selective permeability is vital for processes like osmosis.
• This ability helps cells regulate the internal concentration of different molecules.

Through osmosis, water travels from a region of low solute concentration to a region of high solute concentration, moving across this membrane.
The selective nature of the membrane ensures that solutes cannot pass freely, highlighting the importance of such membranes in biological systems.

Solute Concentration

Solute concentration refers to the amount of solute present within a given volume of solution.
In the context of osmosis, it's crucial to understand that water moves across a membrane to balance out solute concentrations on both sides.

• High solute concentration areas have more solute particles relative to water molecules.
• Low solute concentration areas have fewer solute particles relative to water molecules.

In osmosis, water moves from the side with lower solute concentration to the side with higher solute concentration.
This movement continues until solute concentrations on both sides equalize or until equilibrium is reached.

Osmotic Pressure

Osmotic pressure is a term used to describe the "pulling" force that solutes exert on water molecules when separated by a selectively permeable membrane.
Higher solute concentrations correspond to a higher osmotic pressure.

• Osmotic pressure acts as the driving force for water movement during osmosis.
• The side with more solute exerts a stronger pull on water molecules.

Water naturally moves towards the side with higher osmotic pressure to achieve balance, aiming to dilute the solute and lower its concentration.
Identifying which side has a higher osmotic pressure allows prediction of the water movement direction across the membrane. Understanding this concept helps explain why cells become turgid or flaccid under different solute concentrations.