Movement Across the Membrane

Active and Passive

Diffusion

is the movement of molecules from a region of high concentration to a region of less concentration

Diffusion Animation Click to remove the lid to see the spontaneous movement

Concentration Gradient

Movement of molecules from regions of high concentration to regions of low concentration

Movement

Passive Transport

No energy by the cell– Diffusion– Osmosis– Facilitated Diffusion

Active Transport

Energy by the cell– active pumps

Semipermeable Membranes

allow some things to pass through them but prevent other things from passing through.

Which way will the water go?

Impermeable= = permeable

OSMOSIS

Is the diffusion of water through a semipermeable membrane.

Diffusion and Osmosis Animations

Semipermeable to what?

Will Allow

oxygen water Carbon Dioxide Ammonia glucose, amino-acids

Will NOT Allow

larger molecules like

Sucrose Starch protein

Move freely

Selectively Permeable

Osmosis Animation

Osmosis DemonstrationWhat is happening to the Water?

(blue)What is the difference between the

dissolved substances red and green?

Types of Solutions

Isotonic: The solutions being compared have equal concentration of solutes.

Hypertonic: The solution with the higher concentration of solutes.

Hypotonic: The solution with the lower concentration of solutes.

Types of Solutions

Isotonic, hypertonic, and hypotonic solutions animations

DO WORKSHEET OF Red Blood Cells

(Drop Cell into solution animation) and Osmometer, then click on this animation Osmometer en Francais (refer to worksheet)

With Red Blood Cells

Hypotonic Isotonic Hypertonic

Osmosis Animation

Osmosis Animation Click to view movies, replay

Some Common Examples of Osmosis

Absorption of water by plant roots. Reabsorption of water by the proximal and

distal convoluted tubules of the nephron. Reabsorption of tissue fluid into the venule

ends of the blood capillaries. Absorption of water by the alimentary canal

— stomach, small intestine and the colon.

Equilibrium

No Net change in the flow of water in and out

Elodea (Anacharus)

Common Aquarium Plant

Leaves are one cell thick

Cell Wall Permeability

The cell wall, although strong and rigid, is completely permeable to water and dissolved minerals.

Most green plants do not have woody stems to hold them up, but depend on

cell turgor - the stiffness given to cell walls by being full of water - to give them rigidity.

Unlike animal cells, plant cell have a cellulose cell wall surrounding the cell membrane

Turgid vs. Flaccid

The turgid cells in turn press against the packing tissue or cortex of the plant stem - giving stiffness to the stem and holding the plant upright.

As the cells lose water their internal pressure drops and they lose shape, becoming flaccid. The plant will droop and wilt.

Stained Water Vacuoles

Turgid Plant Cells Flaccid Plant Cells (or plasmolysed)

Elodea

Osmosis in Elodea

Were you right?

Passive Transport

Does not require energy

No Energy Required

Facilitated Diffusion

Facilitated Diffusion

Protein Channels that allow specific substances to pass through

carrier protein for glucose

can also be other channels for ions

Active Transport

Molecules moved across the membrane “against the gradient” (from low concentration to high concentration)

This requires the cell to expend energy

Active Transport Animation

Active Transport(against the gradient)-Lo to Hi Concentration

Fewer on outside

More on inside, but will move in

Uses Energy

Sodium Potassium Pump

Sodium Potassium Pump and Proton Pump animations

NOTE THAT THESE ARE EXAMPLES OF ACTIVE TRANSPORT (require the cell to use ATP)

Contrast

Endocytosis/exocytosis

Endocytosis

Bringing food in by pinching off the membrane

Phagocytosis

Pinocytosis

Cell engulfs small, liquid molecules.

Receptor Mediated

Macromolecules bind to receptors on the surface of the cell.

Receptors with bound macromolecules aggregate in one area and are brought

into the cell by endocytosis.

Exocytosis

Pinching off the membrane to remove wastes “Cell pooping”

Exocytosis Animation

REVIEW ANIMATIONS

Transport Across Membrane Animations

Excellent Endo and Exo Video Clips

REVIEW PICTURES

MEMBRANE TRANSPORT QUIZ

What is this?

What type of membrane transport?

What is this showing?

Why is the water moving in?

Why is the water moving out?

Will the water in the cell in the diagram at left flow out, in, or in and out equally?

What has happened to this cell?

What is this called?

What is this called?

As Osmosis Jones Would Say

Keep Moving!