Simple diffusion, facilitated diffusion, and osmosis; active transport, endocytosis, and exocytosis; and how the need to exchange materials across membranes influences cell size and shape. Introduction: The movement of molecules across cell membranes occurs either by diffusion with the fluid phospholipid bilayer or with the help of transport proteins. The diffusion of molecules occurs from higher to lower concentration. And the rate of diffusion is directly proportional to the temperature. The plasma membranes are selectively permeable as the proteins mosaic only lets some selective molecules to pass through it. This selective permeability occurs in two ways- (1) Passive transport , in which the movement of molecules across the membranes occurs by diffusion along the concentration gradient. (2) Energy-requiring transport , in which the movement of molecules across the cell membranes, against the concentration gradient, is facilitated by the expense of energy by the cell. Passive transport includes osmosis, facilitated diffusion, and simple diffusion. On the other hand, energy-requiring transport includes exocytosis, endocytosis, and active transport.

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Chapter 5.2, Problem 1CYL

Summary Introduction

To explain:

Simple diffusion, facilitated diffusion, and osmosis; active transport, endocytosis, and exocytosis; and how the need to exchange materials across membranes influences cell size and shape.

Introduction:

The movement of molecules across cell membranes occurs either by diffusion with the fluid phospholipid bilayer or with the help of transport proteins. The diffusion of molecules occurs from higher to lower concentration. And the rate of diffusion is directly proportional to the temperature.

The plasma membranes are selectively permeable as the proteins mosaic only lets some selective molecules to pass through it. This selective permeability occurs in two ways-

(1) Passive transport, in which the movement of molecules across the membranes occurs by diffusion along the concentration gradient.

(2) Energy-requiring transport, in which the movement of molecules across the cell membranes, against the concentration gradient, is facilitated by the expense of energy by the cell. Passive transport includes osmosis, facilitated diffusion, and simple diffusion. On the other hand, energy-requiring transport includes exocytosis, endocytosis, and active transport.

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