Chapter 1.5 Transport Mechanisms Osmosis Cells Chapter 1.5 Transport Mechanisms Osmosis

Osmosis osmo- = water

Osmosis – A perfect definition! THREE KEY IDEAS: A net movement of water. Occurs across a semi-permeable membrane Water moves from an area of HIGH CONCENTRATION of water to an area of LOW CONCENTRATION of water. Simply Perfect!

PASSIVE MOVEMENT OF WATER 2. Semi-permeable membrane 1. Net movement of water 3. Concentration gradient

TONICITY Tonicity compares concentrations of solute. 1 HYPOTONIC 2 ISOTONIC 3 HYPERTONIC

Word Work! Hyper- = above, over, in excess Hypo- = low, under, beneath

HypOtonic Solution Lower solutes in solution when compared to the cell. Causes water to ENTER cell and swell.

Isotonic Solution Equal solutes in solution and cell. Equal movement of water in and out.

Hypertonic Solution Greater solutes in solution when compared to the cell. Causes water to be drawn out of cell and shrink.

‘Cell’ Bag Example

‘Cell’ Bag Example

In Summary TONICITY SOLUTE CONC. WATER CONC. DIAGRAM HYPOTONIC LOW HIGH HYPERTONIC

REVISUAL!!!

Hypo to Hyper…

Osmosis in Living Organisms Plant cells behave differently from animal cells when placed in solutions of different water concentrations. Same water concentration High water concentration Low water concentration

REMEMBER

What is INCORRECT in the diagram below? Pause and Think What is INCORRECT in the diagram below? HypOtonic

Hypo- , Hyper- or Iso- tonic?! The cells below were placed in solutions of unknown concentration. Determine the tonicity of each solution.

Effect of Osmosis on Cells

Diffusion vs. Osmosis

Pause and Think Red blood cells are placed in solutions of different sugar concentration. Explain the result. (3)

Pause and Think Fresh cherries are fleshy and juicy. Candied cherries are prepared by placing fresh cherries in a very strong sugar solution. Explain why candied cherries lose their fleshy texture. (3)

Let’s ANALYSE OSMOSIS EXPERIMENTS!!!

Experiment 1: The Potato Osmometer!

Experiment 1

What results would you expect to see after a few hours? PREDICT: What results would you expect to see after a few hours? Salt Cavity Sugar Cavity Empty Cavity Boiled +

Cavity fills with liquid Cavity fills with liquid OBSERVE: Cavity fills with liquid Cavity fills with liquid Cavity remains dry Salt remains solid

Provide an explanation for each of the results that you observed. EXPLAIN: Provide an explanation for each of the results that you observed. Salt Cavity Sugar Cavity Empty Cavity Boiled + The salt cavity provided a hypertonic external environment. Water in the cytosol of cells nearby exits the cell via osmosis from high concentration of water to low concentration of water. Therefore the escaping water filled the cavity, as observed. The sugar cavity provided a hypertonic external environment. Water in the cytosol of cells nearby exits the cell via osmosis from high concentration of water to low concentration of water. Therefore the escaping water filled the cavity, as observed. The empty cavity had no effect in the concentrations of solute inside or outside of cells. This environment was isotonic for cells and so there is no net movement of water into or out of the cell. The cavity therefore remains empty. Boiling the potato results in destruction of the plasma membrane of cells. Membrane transport is not efficient and so water cannot travel to reach the salty cavity.

Experiment 2: Sliced Potatoes

Experiment 2

EXPLAIN: Provide an explanation for the results that were observed in the picture. Experiment Result Explanation Potato in Distilled Water Potato slice has a firm shape. Potato in Salty Water Potato slice bends easily.

Experiment 3: Celery

Experiment 3 Distilled Water Salty Water 4 hours 4 hours

Celery in Distilled Water EXPLAIN: Provide an explanation for the results that were observed in the picture. Experiment Result Explanation Celery in Distilled Water Celery in Salty Water

Experiment 4: Sugar Bags

Experiment 4 Determine the tonicity of the water in the beaker. Determine the tonicity of the glucose solution in the dialysis tubing. Will water move INTO or OUT of the dialysis tubing? Explain. Will glucose move INTO or OUT of the dialysis tubing? Explain.

Experiment 4 - Answers Determine the tonicity of the water in the beaker. Determine the tonicity of the glucose solution in the dialysis tubing. Will water move INTO or OUT of the dialysis tubing? Explain. Will glucose move INTO or OUT of the dialysis tubing? Explain. hypotonic hypertonic IN NO MOVEMENT because too LARGE!

Experiment 5: Egg Osmosis

concentrated salt solution Experiment 5 concentrated salt solution water egg contents egg contents After 2 days

Celery in Salt Solution EXPLAIN: Provide an explanation for the results that were observed in the picture. Experiment Result Explanation Egg in Distilled Water Celery in Salt Solution