2. Cell Membrane
Also known as the plasma
membrane
In both plant and animal cells
Main function: to protect the
cell
Made of a lipid (fat) double
layer with special embedded
proteins
3.
4. Cell Transport
The membrane also controls
what goes in or out of the
cell (cell transport)
It is semi-permeable
Some molecules, like oxygen &
water, are permeable go
directly through the membrane
Other molecules, like glucose &
salt, are impermeable and only
pass through a protein
5. Cell Transport
There are lots of ways substances enter or exit a cell
It depends on the size of the substance:
Small Particles move through the membrane by:
Passive or Active Transport
Large Particles move through the membrane by:
Endocytosis or Exocytosis
6. Passive Transport
Does not require energy (thus passive…)
Two Types
1. Diffusion
2. Facilitated Diffusion
7.
8. 1) Diffusion
Diffusion is when
molecules spread from an
area of high
concentration to an area
of low concentration
This is called a
concentration gradient
9. 1) Diffusion
Think about spraying air freshener
into a room. It gradually spreads out.
Same thing if someone farts…
Or, if we pushed everyone here into
a corner, but let you move where
you wanted, you would tend to
spread out around the room instead
of staying crammed into the corner.
You’re moving from an area of high
concentration (the corner) to an area
of low concentration (the rest of the
room).
11. 1) Diffusion
Diffusion occurs in cells through the membrane.
Oxygen needed for cellular respiration enters cells by diffusion
CO2 produced by cellular respiration leaves cells by diffusion.
12. Osmosis
Osmosis is when water diffuses through a
membrane.
Think about how important it is for water to get into
and out of cells.
13. 2) Facilitated Diffusion
Sometimes, molecules can’t get
through the membrane without a
little help (facilitation…)
In facilitated diffusion, a special
protein embedded in the
membrane helps molecules move
across
No energy is required, this is still
passive transport
Molecules such as glucose, sodium
& chloride ions get into the cell this
way
14. Active Transport
Requires energy (ATP)
Sometimes, cells have to move a substance against the
concentration gradient or from an area of low to high
concentration
15. Active Transport
Active transport also occurs through a special protein or pump,
like with facilitated diffusion
This is one of the main reasons why cells require energy – they
need the ability to remove substances.
For example, kidney cells filter & remove salt from your blood
through active transport.
17. Large Particles
Sometimes particles are too big to simply cross the membrane.
Instead, they must get pulled into or pushed out of the
membrane in one of two ways
1.
2.
Endocytosis
Exocytosis
18. 1) EndoCytosis
Occurs when large particle(s) are
captured by a pocket in the
membrane
The particle is too big to fit
through a protein channel
The pocket breaks off & forms a
package that moves into the cell
Requires energy
Essential nutrients, like iron, are
absorbed into cells this way
20. 2) ExoCytosis
Occurs when a large bit of
material needs to be removed
from a cell
A package of the materials travels
through the cell to the membrane,
joins it, and is expelled
Opposite of endocytosis
Requires energy
Cells use this to flush out waste
such as hormones
22. Big Ideas
1.
What are two functions of the cell plasma membrane?
2.
What types of substances need to be transported across the
membrane?
3.
How does a particle’s size affect how its transported through
a cell?
4.
List 3 differences between passive & active transport.
