Maintaining a Constant Cell Environment 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

100 mL of pure water or 100 mL saltwater? 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

PLASMOLYSIS CYTOLYSIS

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

Facilitated Diffusion High Concentration of substance Low Concentration of substance

Passive and Active Transport Passive transport – diffusion down a concentration gradient without using energy from cell EXAMPLE: Like riding the bike down the hills high concentration Low concentration

high concentration Low concentration Active Transport- movement of materials against a concentration gradient Riding a bike up a hill high concentration Low 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