Cell Boundaries
Essential Question:
How do the materials needed for life
get in and out of cells?
Warm Up: What’s the difference
between diffusion and osmosis?
How does osmosis affect movement of water in and out of cells?
• Water tends to move in or out of cells by osmosis in such
a way as to reach equilibrium (equal concentrations
inside and outside)
Organelle
Functions
cell membrane
Outer covering of cell,
controls what goes in and
out.
Animal Cell
Analogy
Your skin
Plant Cell
Organelle
Functions
Thick outer wall of plant
cells. Provides protection
and support.
cell wall
Analogy
Brick wall,
Cereal box
Cell wall
Animal Cell
Cell membrane
Plant Cell
Close-up of Cell Membrane
Osmosis & Diffusion
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation_
_how_osmosis_works.html
5. How is osmosis related to diffusion?
• Diffusion = movement
of molecules from
area of high
concentration to low.
Equilibrium
(equally
spread out)
Red food coloring diffuses through a glass of water
• Osmosis = diffusion of
water molecules
across a membrane.
Water moves by osmosis from left to right
6. A red blood cell is 80% water. What would happen if red blood cells
were put into each of the three beakers shown below? Label the
appropriate solutions as hypotonic, hypertonic, or isotonic. Then
describe how osmotic pressure would affect the blood cells placed in
each.
80%
80%
water
water
100% water
Hypotonic
More water moves
into cell than out,
Making it swell
80%
water
80% water
20% salt
65% water
35% salt
Isotonic
Hypertonic
Water moves in & out
of cell at same rate,
So cell stays same size
More water
moves out of cell
than in,
Making it shrink
Maintaining water balance
Sea water
Fresh water
Which jar contains pure water? Salt water? Corn syrup?
A
B
C
corn syrup
(hypertonic)
More water diffused
out of egg
pure water
(hypotonic)
More water
diffused into egg
salt water
(isotonic)
Water diffused in
and out of egg
equally.
7. What is facilitated diffusion? Copy the diagram in Figure 7-17
and use it to explain how facilitated diffusion is used to move
glucose into cells.
Facilitated diffusion = Protein channels help molecules
diffuse into or out of cell
8. Given that a starch molecule can
be hundreds of times bigger than a
glucose molecule, would it be easy
or difficult for starch in your
bloodstream to get inside your
cells? Explain.
Difficult.
Starch molecule too big
to get through holes in
cell membrane.
starch
Glucose
(sugar)
How is a colander like a cell membrane?
Both are selectively permeable; they let small things through, but
not big things.
9. What’s the difference between active and passive transport in cells?
Active or passive?
Active: requires energy
Passive: does not
require energy
9. What’s the difference between active and passive transport in cells?
• Active requires energy from cells. Moving materials
from area of low concentration to high.
• Passive requires no energy from cells, happens by itself.
Moving materials from high concentration to low.
10. Apply what you’ve learned here to explain why you shouldn’t
drink sea water if you’re stranded on a raft in the middle of the
ocean.
Cells will lose water and shrink, you will get dehydrated.
What do you think caused the elodea cells to change as they
did after adding salt water?
• Cells became dehydrated, water moved out of cells.
Cell membrane contracted around chloroplasts.
Before adding salt water
After
Questions?
Video: Active & Passive Transport
http://www.youtube.com/watch?v=kfy92hdaAH0
More videos
Diffusion & osmosis
http://www.youtube.com/watch?v=OXCKjhE1xco
Active & passive transport
http://www.youtube.com/watch?v=qotIWgL7zFs