CELLULAR TRANSPORT

Chapter 3, Section 2

• Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.

Osmosis: Diffusion of WaterOsmosis: Diffusion of Water

• In a cell, water always moves to reach an equal concentration on both sides of the membrane.

• The diffusion of water across a selectively permeable membrane is called osmosis.

Osmosis: Diffusion of WaterOsmosis: Diffusion of Water

• Regulating the water flow through the cell membrane is an important factor in maintaining homeostasis within a cell.

Passive TransportPassive Transport• When a cell uses no energy to move particles

across a membrane passive transport occurs.

Concentration gradientPlasma

membrane

Passive Transport by proteinsPassive Transport by proteins

• Passive transport of materials across the membrane using transport proteins is called facilitated diffusion.

Plasma membrane

Channel proteins

Concentration gradient

Passive Transport by proteinsPassive Transport by proteins

• Some transport proteins, called channel proteins, form channels that allow specific molecules to flow through.

Plasma membrane

Channel proteins

Concentration gradient

Passive transport by proteinsPassive transport by proteins

• The movement is with the concentration gradient, and requires no energy input from the cell.

Concentration gradient

Plasma membrane

Step 1 Step 2

Carrier proteins

Passive transport by proteinsPassive transport by proteins

• Carrier proteins change shape to allow a substance to pass through the cell membrane.

Concentration gradientPlasma

membrane

Step 1 Step 2

Carrier proteins

Passive transport by proteinsPassive transport by proteins

• In facilitated diffusion by carrier protein, the movement is with the concentration gradient and requires no energy input from the cell.

Plasma membrane

Step 1 Step 2

Carrier proteins

Concentration gradient

Active TransportActive Transport

• Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell.

Plasma membrane

Concentration gradient

Carrier proteins

Cellular energy

Step 1 Step 2

How active transport occursHow active transport occurs

• In active transport, a transport protein called a carrier protein first binds with a particle of the substance to be transported.

Plasma membrane

Concentration gradient

Carrier proteins

Cellular energy

Step 1 Step 2

How active transport occursHow active transport occurs

Click image to view movie.

How active transport occursHow active transport occurs

• Each type of carrier protein has a shape that fits a specific molecule or ion.

Plasma membrane

Concentration gradient

Carrier proteins

Cellular energy

Step 1 Step 2

How active transport occursHow active transport occurs• When the proper molecule binds with the

protein, chemical energy allows the cell to change the shape of the carrier protein so that the particle to be moved is released on the other side of the membrane.

Step 1 Step 2

Carrier proteins

Cellular energy

Plasma membrane

Concentration gradient

How active transport occursHow active transport occurs• Once the particle is released, the protein’s

original shape is restored.

Step 1 Step 2

Carrier proteins

Cellular energy

Plasma membrane

Concentration gradient

• Active transport allows particle movement into or out of a cell against a concentration gradient.

How active transport occursHow active transport occurs

Click image to view movie.

Transport of Large ParticlesTransport of Large Particles

• Endocytosis is a process by which a cell surrounds and takes in material from its environment.

Endocytosis Exocytosis

Digestion

Nucleus

Wastes

Transport of Large ParticlesTransport of Large Particles

• The material is engulfed and enclosed by a portion of the cell’s membrane.

Exocytosis

Digestion

Nucleus

Wastes

Endocytosis

Transport of Large ParticlesTransport of Large Particles

• The resulting vacuole with its contents moves to the inside of the cell.

Exocytosis

Digestion

Nucleus

Wastes

Endocytosis

Transport of Large ParticlesTransport of Large Particles

• Exocytosis is the expulsion or secretion of materials from a cell.

Endocytosis Exocytosis

Digestion

Nucleus

Wastes

Transport of Large ParticlesTransport of Large Particles

• Endocytosis and exocytosis both move masses of material and both require energy.

Endocytosis Exocytosis

Digestion

Nucleus

Wastes