Matilda's Cells — Osmosis Lab Simulation

Your task: Matilda's red blood cells have an internal solute concentration that is unknown to you. Drop a sample of her cells into baths of varying NaCl concentration, measure the mass change after 30 minutes (simulated), and use your data to determine the isotonic point of her cells.

Set Up Your Trial

Choose a bath (% NaCl):

Sample

Cell sample mass: 1.000 g

Equilibration time: 30 min (simulated in ~12 sec)

Bath: — % NaCl

t = 0 min

Current mass: 1.000 g

0.0% change

Your Data

Trial	Bath (% NaCl)	Initial Mass (g)	Final Mass (g)	% Change
No data yet — run a trial!

Tip The isotonic point is where the line crosses 0% change.

Now apply what you learned. Matilda has cystic fibrosis. Her airway cells can't pump chloride (Cl⁻) ions out the way healthy cells can. Below, watch what happens to the airway surface liquid (ASL) — the thin watery layer beneath the mucus — in healthy vs. CF airways. Pay attention to where water goes and why.

Healthy Airway

CFTR channels actively pump Cl⁻ out of cells into the ASL. Water follows by osmosis. ASL stays well-hydrated. Mucus is thin and mobile — cilia can sweep it (and trapped bacteria) up and out.

Cystic Fibrosis Airway

CFTR is broken. Cl⁻ stays inside cells. No osmotic gradient is built — water doesn't move into the ASL. The ASL collapses, mucus becomes thick and sticky, and cilia can't move it. Bacteria accumulate.

Connect it back

In Part 1, you placed Matilda's red blood cells in baths of different concentration and watched water move across the membrane to balance solute concentrations. That same principle is at work in her airways every minute of every day — but with a broken CFTR channel, the gradient is never built. The osmosis problem you measured in Part 1 is exactly the mechanism that makes Matilda's lungs vulnerable to chronic infection.

Discussion In your paper, you'll connect your Part 1 quantitative data to the qualitative model in Part 2 — explaining why Matilda's mucus is thick using the principles of osmosis you measured.