Cell Function – Cells and their Environment

Chapter 7, Section 3

L2 Biology

Molecules are always moving Molecules move randomly and bump

into each other and other barriers

Diffusion Movement of molecules from an area of high

concentration to an area of lower concentration (down a concentration gradient).

Continues until equilibrium is reached.

Diffusion

Concentration Gradient

100% - high number

0 % - lower number

Diffusion Occurs without control or energy use – it

is called Passive Transport Affected by:

Size of molecules Size of pores in a membrane Temperature Stirring

Simple Diffusion

LAB – Diffusion

Starch

Water

glucose

Water Iodine

What will happen to the starch?

glucose?

iodine ?

Dialysis tubing – simulates a cell membrane

WHY?

Cell Membranes are Semipermeable Let some molecules pass through and

not others. Small molecules pass through – ex: water Large molecules can’t pass through – ex:

proteins and complex carbohydrates

Which molecules will diffuse?1 2 3 4

5 6

How long does diffusion continue? Until equilibrium is reached:

This means there will be an equal distribution of molecules throughout the space – this is why odors smell strong at first, then seem to disappear

Facilitated Diffusion uses carrier proteins

Carrier proteins in the membrane help the molecules across faster than would be expected by diffusion alone

Facilitated Diffusion:

Osmosis – A Special kind of Diffusion

Diffusion of water across a selectively permeable membrane

Cytoplasm is a solution of water and solutes (stuff dissolved in the water).

Water moves into and out of cells because of the different concentrations of the solutes.

Different kinds of cells react differently to osmosis, depending on the solution they are in:

Hypertonic Solution – More water inside cell than outside

Plasmolysis

Plasmolysis

Cells shrink and die

Iso-osmotic Solution – same concentration of water inside and outside cell

Animal cell

Plant cell

No net gain or loss of water

Hypotonic Solution – more water outside cell than inside

Cytolysis – cell swells and bursts

Builds up turgor pressure – cell becomes stiff, keeping plant upright

Blood in different solutions:

Diffusion in an animal cell:

Osmosis:

Active Transport

Endocytosis Very large molecules or substances must

enter the cell by the membrane pinching inward:

Pinocytosis The cell takes in liquid droplets and

forms a vacuole

Phagocytosis The cell takes in large particles

Exocytosis The cell gets rid of secretions or wastes

The End

Phagocytosis in action – phagocyte (white blood cell)

going after a bacteria cell