Bellringer Humans must have their body temperature at

Bellringer Humans must have their body temperature at a constant temperature. Make a list of ways the body responds when it gets cold.

Chapter 8; Section 1 Cell Membrane Key Ideas: n How does the cell membrane help a cell maintain homeostasis? n n How does the cell membrane restrict the exchange of substances? What are some functions of membrane proteins?

Homeostasis n All living things respond to their environments. n Homeostasis - the maintenance of stable internal conditions in a changing environment. n Occurs in individual cells & organisms n occurs by controlling the movement of substances across the cell membrane.

Cell Membrane n cell membrane n n n fluid made up of a “sea” of lipids in which proteins float. acts as a gatekeeper provides structural support to the cytoplasm recognizes foreign material communicates with other cells

Cell Membrane n made of phospholipids. n phospholipid - a specialized lipid made of a phosphate “head” and two fatty acid “tails. ” n phosphate head n polar n attracted to water n fatty acid tails n nonpolar n repelled by water

Cells and Their Environment Phospholipid Click above to play the video Section 1

Cell Membrane Water outside the cell lipid bilayer - double layer of phospholipids nonpolar tails -Make up the interior -repelled by water n polar heads n attracted to water, so they point toward the surfaces of the lipid bilayer. n One layer faces the cytoplasm, n other layer is in contact with the cell’s immediate surroundings. Water inside the cell

Cells and Their Environment Lipid Bilayer Click above to play the video Section 1

Cells and Their Environment Cell Membrane Click above to play the video Section 1

Cell Membrane & Permeability n n Only certain substances can pass through the lipid bilayer. What determines whether a particle will pass? n n n only small, nonpolar substances can pass Ions Particle size Solubility in water Needs of cell

Membrane Proteins n Various proteins n n Some face inside the cell face outside the cell Others may stretch across the lipid bilayer and face both inside and outside. Proteins are made of amino acids. Some amino acids are polar, and others are nonpolar. n The attraction and repulsion of polar and nonpolar parts of the protein to water help hold the protein in the membrane.

Cells and Their Environment Membrane Proteins Section 1

Membrane Proteins Types of Proteins n cell-surface markers – act like a name tag n receptor proteins – enable the cell to sense its surroundings by binding to certain substances outside the cell n Enzymes – help with biochemical reactions inside the cell n transport proteins. – aid in movements of substances into and out of the cell because some substances cannot pass through the lipid bilayer

Cells and Their Environment Parts of the Cell Membrane Section 1

Summary n n n One way that a cell maintains homeostasis is by controlling the movement of substances across the cell membrane. The lipid bilayer is selectively permeable to small, nonpolar substances. Proteins in the cell membrane include cellsurface markers, receptor proteins, enzymes, and transport proteins.