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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