Cells and Their Environment
Chapter 4
p 74-84
Homeostasis
• A biological balance
• Cells, tissues, organs, and organisms must
maintain a balance.
• Cells do so by controlling and regulating what gets
into and out of the cell.
Transport
• Active
• Passive
• The movement of
any substance across
a cell membrane with
the use of chemical
energy
• Transport that does
not require chemical
energy to occur
• ie: diffusion and
osmosis
– ie: Na+/K+ pump
DIFFUSION
• Process by which molecules spread from an
area of high concentration to an area of low
concentration
• Concentration gradient: a difference in
the concentration of a substance
• Examples:
– Beaker of water with food coloring
– Smell of perfume in a room
***Molecules are in constant
motion
Diffusion animations
• http://www.northland.cc.mn.us/biology/Biol
ogy1111/animations/transport1.html
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/c
hapter2/animation__how_diffusion_works.h
tml
Osmosis
• Diffusion of water through a membrane from
an area of high concentration to an area of low
concentration.
What determines the direction in which water
molecules diffusion across a cell membrane?
**the concentration of water and of solutes
dissolved in the solution
• http://www.stolaf.edu/people/giannini/flasha
nimat/transport/osmosis.swf
• http://www.tvdsb.on.ca/westmin/science/sbi
3a1/Cells/Osmosis.htm
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/c
hapter2/animation__how_osmosis_works.ht
ml
• http://www.wiley.com/legacy/college/boyer/
0470003790/animations/membrane_transpo
rt/membrane_transport.htm
Think about it…
What happened if you eat salty foods?
Grass wilts if you add too much
fertilizer…WHY?
Cells can be found in 1 of 3
solutions:
1. HypOtonic
2. Hypertonic
3. Isotonic
HYPOTONIC
• Concentration of
solute molecules in
the environment
outside of the cell is
lower than that in
the cell.
• Water moves in
Red blood cell
Hypertonic
• Concentration of
solute molecules
outside the cell is
greater than that in the
cell
• Water moves out
Isotonic
Conccentration of solute
molecules outside cell
and inside are equal.
**equilibrium
Facilitated diffusion
• Use of carrier to “help” move molecules
across a membrane
• Passive: energy Y or N?
• Gradient: H to L
• Example: glucose
Filtration
• Type of Transport:
Passive
• Using pressure to push
something through the
cell membrane
• Energy needed??
• Example…what organ
in your body filters
Active transport
• Movement of substances through a membrane
from a low to high concentration with the use of
energy.
• ATP: energy form
• Usually Low to high concentration
– “Against a gradient”
• Example: Na/K pump.
Active Transport
• http://www.brookscole.com/chemistry_d/te
mplates/student_resources/shared_resources
/animations/ion_pump/ionpump.html
Some molecules are too large to
pass thru membrane!!! Even with
use of energy
– Endocytosis…moveme
nt of substances into
the cell by transport
vesicles into the cell.
– Exocytosis…
movement of
substances outside of
the cell by transport
vesicles into the cell
Endocytosis
Exocytosis
http://www.coolschool.ca/lor/BI12/u
nit4/U04L05.htm