Chapter 8 – Cellular Transport

Plasma Membrane

• Selectively permeable

• Controls what passes through the membrane

• Made of: phospholipids, proteins, and cholesterol.

Diffusion

• Movement of molecules from a high concentration of molecules to a low concentration of molecules

• Brownian movement: molecules are moving all the time-

(random movement)

Concentration Gradient

• Difference in the concentration of molecules across a space

• Molecules will move until the solute and solvent are mixed evenly

Dynamic Equilibrium

• When the concentration of the molecules are equally distributed

• There is no concentration gradient

• There will still be movement of particles, but no net change

Osmosis

Diffusion of water molecules through a selectively permeable membrane (type of diffusion)

High concentration to…..

Low concentration

Osmosis: Diffusion of WaterOsmosis: Diffusion of Water

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

• Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis.

What controls osmosis?What controls osmosis?

BeforeOsmosis

AfterOsmosis

Water molecule

Sugar moleculeSelectively permeable membrane

3 type of solutions3 type of solutions

Isotonic Solution

Hypertonic Solution

Hypotonic Solution

Cells in an isotonic solutionCells in an isotonic solution• In an isotonic

solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell.

H2OH2O

Water MoleculeDissolved Molecule

This means:

• The concentration of the water is the same inside the cell and outside the cell

• Dynamic Equilibrium has been reached

Cells in an isotonic solutionCells in an isotonic solution

• In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape.

H2OH2O

Water MoleculeDissolved Molecule

Cells in an isotonic solutionCells in an isotonic solution

• A plant cell has its normal shape and pressure in an isotonic solution.

Cells in a hypertonic solution

• In a hypertonic solution, there is a higher concentration of dissolved substances (solute) in the solution than the concentration inside the cell

This means…….

The water concentration is lower outside the cell than inside the cell

Cells in a hypertonic solutionCells in a hypertonic solution

• In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink.

H2O

H2O

Water MoleculeDissolved Molecule

Cells in a hypertonic solutionCells in a hypertonic solution

• Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

Cells in a hypotonic solution

• In a hypotonic solution, there is a lower concentration of dissolved substances (solute) in the solution than inside the cell

This means…..

Water concentration is higher outside the cell than inside the cell

Cells in a hypotonic solutionCells in a hypotonic solution

• In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell.

H2OH2O

Water MoleculeDissolved Molecule

Cells in a hypotonic solutionCells in a hypotonic solution

• Plant cells swell beyond their normal size as pressure increases.

Blood cell

Plant cell

ReviewHypotonic solution-hippo/hypo

Water enters his mouth- looks like he is going to explode

Review• Hyper kids rushing

out of class after 2 hours in 104 degree classroom

• Hyper-Hypertonic- water leaves the cell

Types of Transport

• Passive Transport

• Active Transport

Passive Transport• Movement of particles across membranes by

diffusion - the cell uses NO energy to move the particles - particles move ALONG the concentration gradient

Passive Transport

DiffusionDiffusion

OsmosisOsmosis

Facilitated DiffusionFacilitated Diffusion

High Concentration to Low Concentration

Facilitated Diffusion

• Type of passive transport that uses transport proteins

• Doesn’t use energy

Active Transport

• Transport that requires energy

• Transport of materials AGAINST the concentration gradient High Concentration

Low Concentration

Active Transport

Endocytosis

Exocytosis

Endocytosis

• Phagocytosis- cell engulfs particle with pseudopodia (cell eating)

• Pinocytosis-cell gulps/drinks extracellular fluid (cell drinking)

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 plasma 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

Question 1

B. endocytosis A. active transport

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

Water molecule

Sugar moleculeSelectively permeable membrane

Question 1

D. osmosis C. exocytosis

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

Water molecule

Sugar moleculeSelectively permeable membrane

The answer is D, osmosis. Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within the cell.

Water molecule

Sugar moleculeSelectively permeable membrane

Before osmosis After osmosis

What is the expected result of having an animal cell in a hypertonic solution?

Question 2

D. The cell retains its normal shape.

C. The cell swells up.

A. The cell shrivels up.

B. The plasma membrane shrinks away from

the cell wall.

The answer is A. In a hypertonic solution, cells experience osmosis of water out of the cell. Animal cells shrivel because of decreased pressure in the cells.

H2OH2O

Water moleculeSugar molecule

A grocer mists the celery display with water to keep it looking fresh. What type of solution is the celery now in?

Question 3

D. exotonic

C. hypertonic

B. hypotonic

A. isotonic

The answer is B. Plant cells contain a rigid cell wall and do not burst even in a hypotonic solution.

Plasma membrane

Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________.

Question 4

B. simple diffusion

A. osmosis

Concentration gradient

Channel proteins

Transport of materials across the plasma membrane that does not require energy from the cell but does use transport proteins is called __________.

Question 4

D. active transport

C. facilitated diffusion

Plasma membrane

Concentration gradient

Channel proteins

The answer is C. Facilitated diffusion is a type of passive transport and requires no energy from the cell.

Plasma membrane

Concentration gradient

Channel proteins

End of Chapter 8 Show