Transport of Molecules in a Cell

Terms to Know• SOLUTE: refers to the substance that is to be

dissolved (Salt, Sugar)• SOLVENT: responsible for dissolving the solute

(Water)• SOLUTION: Solvent and solute after combining

together• ECF: Extracellular Fluid. Surrounds all living cells• CONCENTRATION: mass of solute dissolved in the

solvent • SEMI-PERMEABLE (SELECTIVELY-PERMEABLE): a

membrane that allows only some substances in or out

Selectively Permeable Membrane

Transportation of MoleculesActive Transport• Movement of

molecules across a semi-permeable membrane against a concentration gradient with a protein

• ENERGY required

Passive Transport•Movement of molecules across a semi-permeable membrane with the gradient

3 types: Osmosis,Diffusion +

Facilitated Diffusion

•Movement of molecules across a semi-permeable membrane with a protein

•NO ENERGY required

Diffusion• Solute molecules

moving from an area of high concentration to an area of low concentration

• Random motion drives diffusion

• Movement is based on kinetic energy (speed), charge, and mass of molecules

• Equilibrium is reached when there is an even distribution of solute molecules

2

3

14

(water)

High Concentration

Low ConcentrationEquilibrium Reached

Osmosis• Diffusion of water through a semi-permeable membrane

– Permeable to solvents (WATER), but not to large molecules

– High [water] to low [water][concentration]

• Dissolved molecules (i.e. glucose, starch) are called solutes

• REMEMBER:Water = solvent Glucose, Starch, Salt = solutes

Effect of Water on Cells• Hypertonic Environment

– High [solute], low [water]

• Isotonic Environment– [water] = [solute]

• Hypotonic Environment– High [water], low [solute]

OsmosisSucrose will not move but water will

Dialysis Bag Experiment

IodineGlucose

Starch

Dialysis bag

• Dialysis Bag– Semi-permeable

membrane– Water, glucose, & starch

• What passes through the dialysis bag?– Glucose (Benedict’s Test)– Starch (Iodine Solution)

• Time Course Experiment– Every 10 minutes,

measure the amount of glucose & starch present in the beaker

Osmosis in Living Cells

Cellulose in cell wall

Normal plasmolyzed flaccid

turgid

RED BLOOD CELLS

Osmosis in Plant Cells

• Observe Elodea leaves via a wet mount of the sample

10% NaCl

Distilled water

Hypertonic

Hypotonic

Plasmolysis

Recall the Cell Membrane

Proteins in the Plasma (cell) Membrane

Proteins are Specific to certain Solutes

Active Transport

ENDOCYTOSIS

The general term for bringing bulk chemicals into a cell is endocytosis (endo = inside); the general term for bringing bulk chemicals out of a cell is exocytosis (exo=outside).

Moving material into the cell by endocytosis involves the pinching in of a portion of the cell membrane around the material to be transported into the cell. The pinched-in portion eventually breaks free from the cell membrane and forms a vesicle in the cytoplasm.

Homework

• Complete your Cheek Cell & Elodea Cell mini-lab

• Study for your Microscope quiz• Answer questions on p.25 Q.1-19

Next topic: Cell cycle & cell division