The Cell Membrane Also known as a “plasma membrane”

Plasma Membrane Controls materials entering and leaving the cell Helps regulate homeostasis Plasma membrane has selective permeability

similar to a window screen

Made of phospholipids with embedded proteins. Phospholipid 

Types of proteins in cell membrane 1.Cell-surface marker: identifies cell type and identifies cells as “self”.

2. Receptor Protein: recognizes and binds to substances outside the cell

3.Enzyme: Assists chemical reactions inside the cell Example: sucrase and maltase are embedded into cells of the small intestine, where they digest disaccharides

4. Transport protein: Helps substances move across cell membrane.

Cellular Transport Sections 3-4 and 3-5

I. Passive Transport Materials move across membranes because of a concentration gradient. Does not require energy.

Diffusion is a type of passive transport. Molecules move from an area of high concentration to an area of low concentration. A. Diffusion

Continues until equilibrium is reached

B. Osmosis How is osmosis different from diffusion? It only deals with movement of water

Isotonic: same concentration of dissolved particles inside and outside of cell; cell stays the same size Three Types of Solutions Hypotonic: less dissolved particles outside cell than in cell; cell gains water and swells Hypertonic: more dissolved particles outside cell than in cell; cell loses water and shrinks

Osmosis in Plant cells

Practice Problem: Sea water has a higher concentration of salt than human body cells have. Why might drinking large amounts of sea water be dangerous for humans?

Facilitated diffusion is passive transport of materials across the plasma membrane with the aid of transport proteins. Molecules such as sugars or amino acids enter the cell through facilitated diffusion Channel protein shown at right – provides a tubelike opening for small molecules C. Facilitated Diffusion

Carrier proteins change shape to let larger molecules into the cell

Cells use energy to transport materials against the concentration gradient II. Active Transport

Active transport is powered by chemical energy (ATP). Active Transport Active transport occurs through transport proteins

A cell can import large materials in vessicles during the process of endocytosis. Cells use energy to transport material in vessicles. Endocytosis

Exocytosis Exocytosis is the process of expelling material from the cell.