The cell membrane is “semi-permeable”, which means that it regulates the passage of materials into and out of the cell.

Cells maintain a balance between themselves and their environment. This balance is called equilibrium. The cells can adjust to changes in their environment, but there is a limit to the amount of change.

Molecules are in constant motion Molecules are in constant motion. As they move, they tend to go to areas that are less crowded or “less concentrated”. Molecules always spread from an area of higher concentration to an area of lower concentration. High concentration of sugar  Low concentration of sugar  Equal concentration of sugar all over 

Two examples of diffusion & passive transport (no energy required). Perfume / scent around a room Food coloring in water

In diffusion and osmosis, the molecules move “downhill” or with the concentration gradient. Notice how no energy is required to move in passive transport. High Concentration Diffusion Low Concentration

How long will molecules continue to move in diffusion and osmosis? Until they are evenly distributed. This is known as equilibrium. (They will continue moving forever, but you will not notice the motion once they are evenly mixed).

Molecules don’t only move in liquid or gas as we demonstrated. They can also diffuse across the cell membrane (which is semi-permeable). Particles (circles) will move from inside to outside until there is an equal amount of particles on either side of the membrane INSIDE CELL OUTSIDE CELL

The ability of a molecule to pass through a membrane depends on two things: The size of the molecule The structure of the membrane it is trying to pass through “Semi-permeable” membranes regulate which molecules enter and which molecules exit the cell.

Other Terms PERMEABLE – lets anything in/out SEMI – PERMEABLE – lets some thing in/out IMPERMEABLE – lets nothing in/out

In facilitated diffusion, molecules too big to fit through the membrane directly will instead pass through special protein “channels” or “carrier proteins” in the cell just for these molecules. Like diffusion, it does not require energy.

When molecules move across a cell membrane to establish equilibrium, it is called diffusion. When water moves across a cell membrane, it is called osmosis. Water will enter a cell or leave a cell depending on the concentration of water inside the cell and in the surrounding environment.

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Isotonic Environment The concentration of water is equal inside and outside of the cell. Water enters and leaves equally.

Hypotonic Environment The concentration of water is higher outside of the cell. More water enters than leaves. “hypo-” means “below” or “under” What are some other words that start with “hypo-”? Hypodermic, hypothermia, hypoallergenic, hypoxia, hypoglycemic

Hypertonic Environment The concentration of water is lower outside of the cell. More water leaves than enters. “hyper-” means “above” or “higher” What are some other words that start with “hyper-”? Hyperactive, hyperextend, hypertension, hyperbaric, hyperbole, hyperglycemic, hypersensitive, hypersonic, hyperventilate

______Isotonic______ Draw this cell in far left column under “Draw and label the environments below as isotonic, hypotonic, or hypertonic”. ______Isotonic______ Label below what might happen to the cells as nothing, swell, shrink, or burst. ______nothing______ Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium. ______equilibrium______ What will the cell look like in a little while? (Draw below)

______Hypotonic______ Draw this cell in far left column under “Draw and label the environments below as isotonic, hypotonic, or hypertonic”. ______Hypotonic______ Label below what might happen to the cells as nothing, swell, shrink, or burst. _____swell & burst_____ Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium. ______cytolysis______ What will the cell look like in a little while? (Draw below)

______Hypotonic______ Draw this cell in far left column under “Draw and label the environments below as isotonic, hypotonic, or hypertonic”. ______Hypotonic______ Label below what might happen to the cells as nothing, swell, shrink, or burst. ______swell______ Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium. ______turgor pressure______ What will the cell look like in a little while? (Draw below)

______Hypertonic______ Draw this cell in far left column under “Draw and label the environments below as isotonic, hypotonic, or hypertonic”. ______Hypertonic______ Label below what might happen to the cells as nothing, swell, shrink, or burst. ______shrink______ Label below what is this called as: turgor pressure, cytolysis, plasmolysis, or equilibrium. ______plasmolysis______ What will the cell look like in a little while? (Draw below)

Nothing Shrink Burst (animal), Swell (plant) Equilibrium Plasmolysis Cytolysis – animal cell bursts Turgor Pressure – plant cell swells

Sometimes molecules the cell needs are too big to diffuse into or out of the cell. The cell must use energy to move these molecules in or out of the cell. When the cell must use energy to bring things in, it is called active transport.

Active transport moves molecules from an area of LOW concentration to an area of HIGH concentration. In other words, they are moving AGAINST the concentration gradient. Notice how energy is required in active transport. High Concentration Active Transport Low Concentration

There are four types of active transport, all of which require energy. Active Transport Video There are four types of active transport, all of which require energy. Endocytosis Cell brings in material Pinocytosis Cell “drinking” Phagocytosis Cell “eating” Exocytosis Cell releases waste Each of these involves bringing materials into the cell except for exocytosis.