Maintaining Homeostasis Cell Membrane Maintaining Homeostasis

Function Controls the movement of substances across the cell membrane.

(b) Structure of the plasma membrane Lipid bilayer Phospholipids Polar heads face out to the external cell environment and to the internal cytoplasm. Lipid tails face each other Outside of cell Inside of cell Hydrophilic region Hydrophobic (b) Structure of the plasma membrane Phospholipid Proteins TEM of a plasma membrane. The plasma membrane, here in a red blood cell, appears as a pair of dark bands separated by a light band. (a) 0.1 µm

Imbedded Proteins 4 Types Carbohydrate tags identify the cell Receptors signal changes to the cell Enzymes assist in chemical reactions Transport proteins move substances through the cell membrane

Passive Transport Diffusion moving substances from areas of high concentration to low concentration Osmosis moving water from a dilute concentration to a high concentration Requires no energy

Active Transport Protein Pumps – move molecules through the membrane Endocytosis – carries substances into the cell in vessicles Exocytosis – carries substances out of the cell in vessicles Requires energy