Chapter 4 Cells and Their Environment Objectives-What you need to know!!!! Related concentration gradients, diffusion, and equilibrium. Predict the direction of water movement into and out of cells. Describe the importance of ion channels in passive transport. Identify the role of carrier proteins in facilitated diffusion.

Passive transport Diffusion-Maintaining homeostasis by controlling the movement of substances across the cell membrane. Diffusion-Movement of a substance from an area of high concentrations to low concentrations. Note above.

Passive transport-Movement across the cell membrane that does not require energy from the cell. – Concentration gradient-The difference in the concentration of a substance across a space. Equilibrium-Concentration of a substance is equal throughout a space

Let’s talk about other example of diffusion Osmosis-The diffusion of water through a selectively permeable membrane. It is a type of passive transport.

3 types of Osmosis Hypertonic solution-A solution that causes a cell to shrink because of osmosis. Hypotonic solution-A solution that causes a cell to swell because of osmosis. Isotonic-A solution that produces no change in cell volume because of osmosis.

Hypotonic, Hypertonic, and Isotonic is very important. Let’s look over page 77 and at the potato slices. Which potato is in an hypotonic solution, hypertonic solution, and isotonic solution. Look at the slices in solutions. Crossing the cell membrane-Recall polar molecules cannot cross the membrane due to the non-polar insides. Of course you know the membrane is selectively permeable.

Crossing the Cell Membrane Diffusion through ion channel Ion channel-A transport protein with a polar pore through which ions can pass. – The ion that enters the pore can cross the cell membrane without contacting the non-polar interior of the lipid bilayer.

Electrical Charge and Ion Transport Know this! – The rate of movement is determined by the concentration gradient of the substance. – Typical cells have a negative charge inside. – An ion’s electrical charge often affects the diffusion of the ion across the cell membrane. – Ion channel gates will close the pores of some ion channels in response to stretching of membrane, change of electrical charge, and the binding of specific molecules to the channel. – Let’s look at the problem on page 79.

Facilitated Diffusion Facilitated diffusion-A type of passive transport. Uses carrier proteins, it moves substances down their concentration gradient without using the cell’s energy! Duh, it says passive What type of things does it move? It moves amino acids and sugars down the concentration gradient. Look at page 80. End of section 1

Active Transport Active transport-The transport of a substance across the cell membrane against its concentration gradient. – Energy is used in the form of ATP!!! – Let’s compare the different types of transport

Sodium-potassium pump Sodium-potassium pump-Transports 3 sodium ions, Na, out of a cell and 2 potassium, K, into the cell. Active transport is needed. Involves a carrier protein. Another illustration is on page 82 in your books.

Movement of vesicles Endocytosis-The movement of substances into a cell by a vesicle, such as proteins and polysaccharides. Exocytosis-The movement of a substance by a vesicle to the outside of a cell. Nerve cells and various glands release proteins using exocytosis

Membrane Receptor Proteins Receptor protein-A protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule. The simplest example is on page 84, let’s go over!!!! Functions of receptor proteins- – Changes in permeability of membrane – Second messengers-Second messengers-Acts as a signal molecule in the cytoplasm. – Enzyme action-May speed up chemical reactions inside the cell. – Let’s go over Key Concepts-Page 87