Osmosis

Diffusion

movement of particles (ions, molecules, or larger compounds) from an area of high concentration to an area of low concentration.

Concentration Gradient

Difference in concentration between two areas.

Equilibrium

Achieved when particles are evenly distributed and no concentration gradient exists.

Osmosis

Diffusion of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

Selectively Permeable Membrane:

Allows certain small molecules (like water) to pass but restricts larger molecules or ions.

Types of cellular transport

passive transport and active transport

Active Transport

-Requires energy (ATP).

-Moves molecules against the concentration gradient (low → high).

Passive Transport

-No energy required.

-Moves molecules with the concentration gradient (high → low).

-Two types studied: Diffusion, Osmosis

cell membrane structure

phospholipid bilayer

Phospholipid bilayer

Hydrophobic (water-fearing) fatty acid tails face inward; hydrophilic (water-loving) phosphate heads face outward.

Amphipathic

Having both hydrophobic and hydrophilic regions.

Integral proteins

Embedded in membrane; channels for transport.

Peripheral proteins

On membrane surfaces; structural support.

Cholesterol

Adds rigidity and structure.

Osmosis and Tonicity:

-Hypotonic

-Hypertonic

-Isotonic

Hypotonic

Lower concentration of solutes outside the cell. Water moves into the cell causing it to swell (lysis in animal cells).

Hypertonic

Higher concentration of solutes outside the cell. Water moves out of the cell causing it to shrink (crenation in animal cells, plasmolysis in plant cells).

Isotonic

Equal concentration of solutes inside and outside the cell. No net water movement.

Effect of Temperature on Diffusion

-the higher the temperature, the faster the diffusion

-the lower the temperature, the slower the diffusion.

Activity 2: Selective Permeability (Dialysis Tubing Experiment)

-The tubing is selectively permeable; starch did not leave the bag because molecules are too large.

-Iodine solution (Lugol's)

Iodine solution (Lugol's)

Moves through dialysis tubing into the bag, turning starch solution purple.

Effect of Concentration on Osmosis

-Bags with higher sugar concentration gained more weight (more water moved in via osmosis).

-Percent change was highest for 40% sugar solution, demonstrating a direct relationship between concentration gradient and rate of osmosis

Why do flowers smell stronger when you're close?

Higher concentration of fragrance molecules close to flowers (diffusion).

How does CO₂ diffusion relate to global warming?

CO₂ diffuses from high-concentration areas (like industrial regions) to lower concentration areas, affecting even remote areas like Antarctica.

Why is selective permeability important?

Controls what enters and exits cells, maintaining homeostasis.

Why is it dangerous to drink too little or too much water?

Too much water → cells swell and burst (lysis).

Too little water → cells shrink (crenation).

Why does salting the earth affect plant growth?

Salt increases solute concentration in soil, causing water to leave plant cells (plasmolysis), plants wilt, and die from dehydration.

Diagram of diffusion

Particles evenly spread over time.

Diagram of Cell membrane

Phospholipid bilayer, integral and peripheral proteins, cholesterol.

Tonicity

Water movement in hypertonic (water out), hypotonic (water in), and isotonic (no net movement) environments.