Movement of Molecules: Diffusion and Osmosis Lab

Selectively Permeable

Allows some substances to pass freely while restricting others.

Diffusion

Net movement of a substance from a region of higher concentration to lower concentration (passive transport, no energy required).

Concentration Gradient

Difference in concentration of a substance between two regions.

Equilibrium

No net change in a system; molecules are evenly distributed but continue to move.

Tonicity

Refers to the solute concentration of a solution outside a cell and its effect on cellular fluid volume.

Steepness

Greater concentration gradient → faster diffusion.

Size

Smaller molecules diffuse faster than larger ones.

Temperature

Higher temperature → faster diffusion.

Density

Higher density → slower diffusion.

Simple Diffusion

Molecules move through air, water, or a solid medium.

Dialysis

Diffusion of a solute across a selectively permeable membrane.

Osmosis

Diffusion of water across a selectively permeable membrane.

Hypertonic

Solution with higher solute concentration.

Hypotonic

Solution with lower solute concentration.

Isotonic

Solutions with equal solute concentration.

Direction of Osmosis

Water moves out of a hypotonic solution and into a hypertonic solution.

Example of Osmosis

A 3% salt solution (hypertonic) will cause water to move out of a 1% salt solution (hypotonic).

Beaker 1 (Distilled Water)

Cell gained weight (hypotonic environment).

Beaker 2 (10% Sucrose)

Cell stayed the same (isotonic environment).

Beaker 3 (20% Sucrose)

Cell lost weight (hypertonic environment).

Beaker 4 (40% Sucrose)

Cell lost weight twice as fast as Beaker 3 (steeper gradient → faster osmosis).

Selectively Permeable

Allows some substances to pass while restricting others.

Diffusion

Movement of molecules from high to low concentration.

Concentration Gradient

Difference in concentration between two regions.

Equilibrium

No net change; molecules are evenly distributed.

Tonicity

Solute concentration of a solution relative to a cell.

Steepness

Greater gradient → faster diffusion.

Size

Smaller molecules diffuse faster.

Dialysis

Diffusion of solutes across a membrane.

Osmosis

Diffusion of water across a membrane.

Hypertonic

Higher solute concentration.

Hypotonic

Lower solute concentration.

Isotonic

Equal solute concentration.

Hypertonic Solution

Water moves out of the cell.

Hypotonic Solution

Water moves into the cell.

Isotonic Solution

No net movement of water.

Effect of Solute Concentration on Osmosis

Steeper gradient → faster osmosis (e.g., Beaker 4 vs. Beaker 3).

Positive Slope

Weight gain (hypotonic environment).

Negative Slope

Weight loss (hypertonic environment).

Substances in Multi-Bag

Salt, glucose, starch, protein.

Diffused Out

Salt, glucose.

Remained Behind

Starch, protein.

Test Reagents

Benedict's Test: Glucose (orange-red = positive). Iodine Test: Starch (bluish-black = positive). Silver Nitrate Test: Salt (milky white = positive). Biuret Test: Protein (purple-violet = positive).

10% Sucrose Cell in 20% Sucrose Solution

Beaker Solution: Hypertonic. Water Movement: Out of the cell.

Graphical Data Interpretation

Beaker 1 (Distilled Water): Positive slope (weight gain). Beaker 2 (10% Sucrose): No slope (no weight change). Beaker 3 (20% Sucrose): Negative slope (weight loss). Beaker 4 (40% Sucrose): Steeper negative slope (faster weight loss).