Understand the structure of the cell membrane, the principles of osmosis, and the function of the cell wall.
Why potatoes shrink in salt water.
If you place a potato slice in plain water, it swells up. But put it in a 20% salt solution, and it shrinks! This happens because the potato's cell membrane is selectively permeable—it acts like a bouncer, allowing water molecules to move across, but blocking the larger salt molecules.
Explanation of the selectively permeable membrane and fluid-mosaic model.
Every living cell is enclosed by a thin boundary called the cell membrane or plasma membrane. It is incredibly thin—only about 7 to 10 nanometres thick!
This boundary defines the individuality of the cell and protects its internal contents.
Diagram of the lipid bilayer and proteins.
The cell membrane acts as a fluid, dynamic boundary protecting the cell.
Define diffusion, osmosis, and concentration gradients.
Molecules naturally tend to spread out. Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration (down a concentration gradient).
This process happens even without a membrane, like perfume spreading through a room.
Visual comparison of cells in different solutions.
How water movement changes cell volume based on surrounding concentrations.
Explain the rigid cell wall in plants, fungi, and bacteria.
While all cells have a cell membrane, the cells of plants, fungi, and bacteria have an additional outer protective layer called the cell wall.
Because plants cannot run away from harsh weather, they need this rigid wall to withstand wind, rain, and environmental stress.
Key terms for cell boundaries.