The Function of Cell Membranes - Biology

1. Fundamental Concepts

Definition: The cell membrane is a thin, flexible layer that surrounds the cell and regulates the movement of substances in and out of the cell.
Functions: Protection, communication, and transport of materials.
Components: Phospholipid bilayer, proteins, and cholesterol.

Selective Permeability: $${\text{Allows certain molecules to pass while blocking others}}$$

Fluid Mosaic Model: $${\text{Describes the structure of the cell membrane as a fluid matrix with embedded proteins}}$$

Transport Mechanisms: $${\text{Includes passive diffusion, facilitated diffusion, active transport, and endocytosis/exocytosis}}$$

Problem: Explain how the cell membrane facilitates the movement of water across it.

The cell membrane contains aquaporins, which are protein channels specifically designed for water molecules.
Water molecules can pass through these channels by osmosis, moving from an area of high concentration to an area of low concentration.

Validation: This mechanism ensures that cells maintain their internal water balance.

Problem: Calculate the rate of glucose uptake by a cell using the formula for active transport.

Identify the concentration gradient and the energy required for transport.
Apply the formula for active transport: $${\text{Rate}} = \frac{{\Delta C}}{{t}} \cdot E$$ where $$\Delta C$$ is the change in concentration, $$t$$ is time, and $$E$$ is the energy input.
Substitute the values: $${\text{Rate}} = \frac{{50 \text{ mM} - 10 \text{ mM}}}{{60 \text{ s}}} \cdot 2 \text{ ATP} = 1.67 \text{ mM/s} \cdot 2 \text{ ATP} = 3.33 \text{ mM/s} \cdot \text{ATP}$$

Validation: The calculated rate matches the expected uptake rate under given conditions.

Visual Strategy: Use diagrams to illustrate the structure and function of the cell membrane.
Error-Proofing: Double-check the direction of transport and the role of specific proteins.
Concept Reinforcement: Relate the functions of the cell membrane to real-world examples, such as the use of membranes in dialysis.