Chapter 5-3

Maintaining a Constant Cell Environment

CELL MEMBRANE

• “Gate-keeper”- helps regulate what enters and leaves the cell

• __________ process by which a stable internal environment is kept

Balloon Demonstration

• Smell the balloon- what do you observe?

• Why is this possible?

Cell Membranes

• Cell membranes are selectively permeable- some things pass through easily and others do slowly or not at all

• Particles are always moving

• Move in straight lines in all directions

• Collide with each other

• Diffusion: movement of molecules or particles from an area of high concentration to an area of lower concentration

• Concentration gradient: difference in concentration between two areas

Osmosis

• OSMOSIS: diffusion of water across selectively permeable membrane from high water concentration to low water concentration

• Osmosis Animation

Osmosis

• Which has a higher water concentration?

100 mL of pure water or 100 mL saltwater?

ANSWER: There are more water molecules in pure water because salt takes up volume

Three types of solutions:

• Hypertonic solution: higher concentration of solutes than the cell

• Hypotonic solution: lower concentration of solutes than the cell

• Isotonic solution: same concentration of solutes as the cell

Effects of Osmosis

• Effects of Osmosis

Turgor Pressure

Turgor (osmotic) pressure- Force exerted outward by the water contained in the cell.

• All cells experience this

Effects of Osmosis

• Plasmolysis- shrinking of cytoplasm caused by osmosis– What type of solution causes this?

• Cytolysis- cell bursts due to too much caused by osmosis– What type of solution causes this?

PLASMOLYSISCYTOLYSIS

Cell membrane

• Composed of lipids, proteins and carbohydrates

• Made up of two layers sandwiched together

• Parts of the membrane are actually “fluid” and move

Functions of proteins

• Transport proteins- allow materials that can’t directly go through membrane to get into the cell

• Receptor- communication for the cell

• Enzymes

• Structural – connect to other cells or to structures inside cell

Selective permeability

• Lipid molecules

• Small molecules- water glucose, amino acids, CO2, oxygen

• What passes through is based on chemical properties of membrane and substance trying to get in

Facilitated Diffusion

• Facilitated Diffusion- transport of substances across membrane through transport proteins

• Specific to substate

High Concentration of substance

Low Concentration of substance

Facilitated Diffusion

Passive and Active Transport• Passive transport – diffusion down a

concentration gradient without using energy from cell– EXAMPLE: Like riding the bike down the hills

Low concentration

high concentration

• Active Transport- movement of materials against a concentration gradient– Riding a bike up a hill

Low concentration

high concentration

Why do cells need active transport?

• Maintain different internal conditions than would occur naturally

• Creating a large gradient can use this for work– Use to generate energy– Conduct nerve impulses– Concentrate substances

Two forms of active transport