1. The Cell in Action

2. Section 1: Exchange with the
Environment
A cell must be able to obtain food and
raw materials and get rid of wastes.
What is diffusion?
Diffusion = the movement of particles
from regions of higher density to
regions of lower density
∗ Cells do not need to use energy for
diffusion

3. Diffusion of Ink in Water
∗ The particles of the dye of the ink slowly diffuse through the
water

4. Diffusion of Water
∗ The cells of organisms are surrounded
by and filled with fluids that are made
mostly of water
∗ Osmosis = the diffusion of water
through a semi-permeable membrane
∗ “semi permeable” means that some
things, but not all, can get through

5. Osmosis, continued
∗ Pure water has highest
concentration of water
molecules
∗ When you mix something
with water, you lower the
concentration of water
molecules.
∗ During osmosis, water
particles move to where they
are less concentrated

6. Diffusion in Action

7. Salt would cause water molecules to travel out of the
cell membrane. Water loss equals dead slugs!

8. The Cell and Osmosis
∗ Osmosis is important
to cell functions
∗ Example: red blood
cells are surrounded
by plasma, which is
made up of water,
salt, sugars, and other
particles. The
concentration of
these particles is kept
in balance by osmosis!

9. ∗ Osmosis also
occurs in plant
cells Example:
when a wilted
plant is watered,
osmosis makes
the plant firm
again

10. Osmosis in Plant Cells

11. Comprehension Question:
∗Why would red blood
cells burst if you placed
them in pure water?

12. Answer:
∗ Red blood cells would burst in pure water because
water particles move from outside, where particles
are dense, to the inside of the cell, where particles
are less dense. This movement of water would
cause red blood cells to fill up and burst!

14. SORRY!
Knowledge does
not diffuse
from the pages
of the textbook
to your brain!

15. Moving Small Particles
∗ Small particles,
like sugar, cross
the cell
membrane
through channels,
which are made
up of proteins

16. Passive Transport
∗ Passive transport = the movement of
substances across the cell membrane
without the use of energy by the cell
∗ During passive transport, particles move
from an area of high concentration to an
area of low concentration
∗ Examples of passive transport : osmosis
and diffusion

17. Passive Transport

18. Active Transport
∗ Active transport = the movement of
substances across the cell membrane
that requires the cell to use energy
∗ Examples of active transport:
endocytosis and exocytosis
∗ involves the movement of particles
from an area of low concentration to an
area of high concentration

19. Endocytosis:
∗ Endocytosis = the
process by which a
cell membrane
surrounds a particle
and encloses the
particle in a vesicle
to bring the particle
into the cell
ENDO = IN and GO

20. Steps of Endocytosis:
1. The cell comes into contact with a
particle
2. The cell membrane begins to wrap
around the particle
3. Once the particle is completely
surrounded, a vesicle pinches off
4. Endocytosis = “within the cell”

22. Exocytosis:
∗ Exocytosis = the process in which a
cell releases a particle by enclosing
the particle in a vesicle that then
moves to the cell surface and fuses
with the cell membrane
EXO = EXIT THE CELL

24. Steps of Exocytosis
∗ Large particles that leave the cell
must be packaged in vesicles.
∗ Vesicle travels to the cell membrane
and fuses with it.
∗ Cell releases the particle to the
outside of the cell
∗ Exocytosis = “outside the cell”

25. Endocytosis & Exocytosis

26. Let’s Review:
1. What part of the cell do materials pass
through to get into and out of the cell?
2. What is osmosis?
3. What are 2 examples of passive transport?
4. Large particles enter the cell by_________
and leave by ______________.

27. Answers:
1. Cell membrane
1. The diffusion of water through the semi-
permeable cell membrane
1. Diffusion and osmosis
1. Endocytosis, exocytosis