Transpor Membran (Pembukaan & Difusi Sederhana)

Main Ideas / Concepts

• The video demonstrates membrane transfer (diffusion/dialysis) using a simulation app, since real membrane diffusion experiments are harder to observe directly.
• A key theme is selectivity: how different molecules cross membranes depending on membrane pore size, described by MWCO (molecular weight cut-off) (e.g., 20, 50, 100, 200 MWCO).
• Whether transport occurs depends on:
  • Molecules being small enough to pass through membrane pores
  • Time-to-equilibrium, when left-side and right-side concentrations balance

Simulation Workflow (Methodology)

• Open the simulation app and, from the initial menu:
  • Skip non-experimental items
  • Go directly to “Experiments”

Virtual Tools / Materials in the App

• Left and right glass beakers (containers for solutions)
• Dialysis membrane placed between the beakers
• Solutions/solutes available:
  • NaCl (sodium chloride)
  • Urea
  • Albumin
  • Glucose
  • Dilute water
• Buttons:
  • Dispenser: add/fill a chosen solution into a beaker
  • Flash: clear/empty the setup
  • Record data: save/store results
  • Start: run the diffusion simulation

General Steps for Each Experiment Run

1. Select the membrane MWCO size and place it between the beakers.
2. Set the left-side solute concentration (via concentration controls).
3. Fill the right side with water (typically so right-side solute starts at 0).
4. Click Next, then click Start to begin diffusion.
5. Observe whether the solute:
   • Cannot diffuse
   • Diffuses and reaches equilibrium, and how long it takes
6. Click Record data before moving on.
7. Use Flash to clear/empty before the next simulation.

Experiments and Key Outcomes

1) NaCl with 20 MWCO Membrane

• Setup
  • Use 20 MWCO membrane
  • Left: NaCl = 9 mM
  • Right: water
• Result
  • NaCl cannot diffuse through the 20 MWCO membrane.
• Implied reasoning
  • The pore size is too small for NaCl under these conditions.
  • If right-side concentration stays 0, transport failed; if it becomes > 0, diffusion succeeded.

2) Prediction Question (NaCl not diffusing)

• Multiple-choice options shown:
  • A: not enough time for diffusion
  • B: the charge on sodium prevents diffusion
  • C: the membrane size is too small
  • D: a steeper concentration gradient is needed
• The answer is deferred (“not discussed in this video”).

3) Urea with 20 MWCO Membrane

• Setup
  • Use 20 MWCO membrane
  • Left: urea = 9 mM
  • Right: water
• Prediction prompt
  • A: very slow
  • B: fast
  • C: not at all
• Result
  • Urea also cannot diffuse through the 20 MWCO membrane (as stated).

4) Prediction: Why glucose/albumin weren’t tested earlier

• Given:
  • Glucose = monosaccharide (6-carbon sugar)
  • Albumin = protein (many amino acids; larger molecular structure)
• Multiple-choice options shown (some wording is unclear in subtitles), but the principle is:
  • Molecules too large relative to membrane MWCO → no diffusion
• The video indicates the “most correct” reasoning is based on size vs MWCO.

5) NaCl with 50 MWCO Membrane

• Setup
  • Use 50 MWCO
  • Left: 9 mM NaCl
  • Right: water
• Result
  • NaCl diffuses and reaches equilibrium (around the 10th minute).
• Repeated at higher concentration:
  • Left: 18 mM NaCl
  • Right: water
• Result
  • NaCl reaches equilibrium again (around the 11th minute).

6) NaCl with 100 MWCO Membrane

• Setup
  • Use 100 MWCO
  • Left: 9 mM NaCl
  • Right: water
• Result
  • NaCl reaches equilibrium (around the 10th minute).

7) Urea with 100 MWCO Membrane

• Setup
  • Use 100 MWCO
  • Right-side urea diffusion setup described with urea = 9 mM (left side appears to be the diluent/water side)
• Result
  • Urea reaches equilibrium (around the 16th minute).

8) Prediction Question: urea vs sodium diffusion rate

• Multiple-choice options:
  • A: Faster than sodium because urea is larger
  • B: Slower than sodium because urea is larger
  • C: Faster than sodium because urea is a small molecule
  • D: Slower than sodium because urea is a small molecule
• The answer is deferred to later discussion.

9) Prediction Question: what albumin molecules can pass through 200 MWCO

• Options presented include combinations of:
  • glucose
  • albumin
• The video defers/recaps for later application.

10) Test with 200 MWCO Membrane: glucose vs albumin

• Setup
  • Switch to 200 MWCO
  • Left: 9 mM glucose
• Result
  • Glucose reaches equilibrium (around the 36th minute).
• Then test albumin:
  • Left: 9 mM albumin
• Result
  • Albumin cannot diffuse through the 200 MWCO membrane (as stated).

Overall Lesson / Takeaways

• MWCO controls selectivity: larger molecules fail to pass; smaller ones can pass if pore size allows.

• Equilibrium time depends on:

  • The solute
  • Membrane conditions (example times mentioned: NaCl ~10–11 min for larger MWCO, urea ~16 min at 100 MWCO, glucose ~36 min at 200 MWCO).

• The simulation uses left/right concentration outcomes:

  • If right-side concentration stays 0, the solute did not pass.
  • If right-side concentration increases toward equality, diffusion occurred until equilibrium.

Speakers / Sources Featured

• Speaker (presenter): Rusoder (name given in the introduction)
• No other speakers or external sources are explicitly identified beyond:
  • The simulation app interface
  • The described dialysis membranes and solutes