Chapter 4

Cell Functions

4.1 Lesson 4.1: Transport

Lesson Objectives

• Describe several methods of transporting molecules and ions into and out of the cell.


• Distinguish between active and passive transport.


• Explain how diffusion and osmosis work.

Check Your Understanding

• What structure surrounds the cell?


• What is the primary component of the cell membrane?


• What does homeostasis mean?

Introduction

All organisms and their cells need to maintain homeostasis. But how can a cell keep a
stable internal environment when the environment around the cell is constantly changing?
Obviously, the cell needs to separate itself from the external environment. This job is
accomplished by the cell membrane. The cell membrane isselectively permeable, or
”semipermeable,” which means that only some molecules can get through the membrane. If
the cell membrane was completely permeable, the inside of the cell would be about the same
as the outside and the cell could not achieve homeostasis.

How does the cell maintain this selective permeability? How does the cell control what
molecules enter and leave the cell? The ways that cells control what passes through the cell