Lesson 7.2: Cell Transport and Homeostasis

Lesson Objectives

• Identify two ways that molecules and ions cross the plasma membrane.
• Distinguish between diffusion and osmosis.
• Identify the role of ion channels in facilitated diffusion.
• Compare passive and active transport.
• Identify the connection between vesicles and active transport.
• Compare endocytosis and exocytosis.
• Outline the process of cell communication.

Introduction

Probably the most important feature of a cell’s phospholipid membranes is that they are selectively permeable. A membrane that is selectively permeable has control over what molecules or ions can enter or leave the cell, as shown in Figure below. The permeability of a membrane is dependent on the organization and characteristics of the membrane lipids and proteins. In this way, cell membranes help maintain a state of homeostasis within cells (and tissues, organs, and organ systems) so that an organism can stay alive and healthy.