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2. A View of the Cell
 Cells maintain homeostasis
 Depends on the movement of materials in and out of
the cell
 Nutrients, waste and ions
 Two factors govern the movement of materials in
and out of the cell
 Diffusion
 The plasma membrane

3. Diffusion
 Diffusion is caused by the random motion of atoms
and molecules
 Types of motion: vibrational, rotational and
translational
 The diffusion of water through a membrane is called
osmosis

4. Diffusion in a Cell
 The direction a molecule travels depends on…
 The concentration gradient
 The function the molecule plays in cell metabolism
 3 situations exist between cells and their
environment based on concentration
 Hypotonic
 Hypertonic
 Isotonic

5. Diffusion in a Cell

6. Diffusion in a Cell

7. The Plasma Membrane
 The plasma membrane separates the cell from its
environment and controls what passes through it
 The fluid mosaic model
 The plasma membrane has a dynamic – ever changing –
structural composition
 A phospholipid bilayer
 Cholesterol
 Proteins

8. Phospholipids

10. The Role of Cholesterol
 Cholesterol
 Rigidity
 Fluidity
 Cholesterol
 Rigidity
 Fluidity
 Cholesterol helps to maintain the proper fluidity of the membrane in
cases of extreme temperature change

11. The Role of Proteins
 Transport proteins
 Move needed substances or waste material through
the membrane

12. Methods of Cellular
Transport
Passive Transport
 Requires no cell energy
 Diffusion
 Osmosis
Active Transport
 Requires the cell to
expend energy
 Used to get necessary
metabolic chemicals
 Particles move against the
concentration gradient or
are too large to pass
through transport proteins

13. Passive Transport –
Facilitated Diffusion
 Channel proteins (a type of transport protein)
create a passage or channel through which
molecules can pass

14. Active Transport
 Carrier proteins (a type of transport protein) bind
with a molecule and uses energy to move it against
the concentration gradient

15. Active Transport
 When a molecule is too large to pass through the
membrane…
 …cells can absorb them by engulfing them
 Endocytosis
 Ex/ White blood cells, feeding
 …cells can excrete or secrete them
 Exocytosis
 Ex/removal of waste, release of cellular product
(neurotransmitters, hormones, enzymes)

16. Endocytosis
 To absorb a large molecule (or organism!) a cell
can…
 …completely engulf it
 Phagocytosis
 https://www.youtube.com/watch?v=aWItglvTiLc

17. Endocytosis
 To absorb a large molecule a cell can…
 …make a small pocket (called a vesicle) out of the
membrane to store it
 Pinocytosis

18. Exocytosis
 When a cell directs the contents of a vesicle out of
the membrane into the extracellular space
 Waste = excretion
 Products = secretion