Brief description of the plasma cell membrane and how materials get into or out of the cell. Appropriate for 7th grade life science.

1. The Cell Membrane

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

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

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).

10. 1) Diffusion

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.

16. Passive versus 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

19. 1) EndoCytosis

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

21. 2) ExoCytosis

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.