Download Cell Function – Cells and their Environment

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
Dialysis tubing –
simulates a cell
membrane
Starch
Water
Water
Iodine
glucose
What will happen to the starch?
glucose?
iodine ?
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
5
3
6
4
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
Phagocytosis in action –
phagocyte (white blood cell)
going after a bacteria cell
The End