Biology

1
Biology

• Chapter 5 Homeostasis and Transport

2
Types of Transport

• Passive Transport
• Diffusion
• Osmosis
• Facilitated Diffusion
• Diffusion through Ion Channels
• Active Transport
• Cell Membrane Pumps
• Endocytosis
• Exocytosis

3
Passive Transport
4
Passive Transport

• The movement of substances across the cell
  membrane without any input of energy by the cell
• Helps to maintain homeostasis

5
Diffusion

• Simplest type of passive transport
• Movement of molecules from an area of higher
  concentration to an area of lower concentration
• Concentration gradient difference in the
  concentration of molecules across space
• Molecules move down the concentration gradient
  from more to less concentrations.
• Driven by kinetic energy

6

• Diffusion animation

7
Equilibrium

• When the concentration of the molecules of a
  substance is the same throughout a space.
• Equilibrium animation

Animation with different temperatures
Another animation
8
Diffusion across membranes

• If a molecule can pass through a cell membrane it
  will diffuse from an area of higher concentration
  to an area of lower concentration.
• Ability to diffuse across a membrane depends on
  size and type of molecule and on the chemical
  nature of the membrane.

Animation
9
Osmosis

• The process by which water molecules diffuse
  across a cell membrane from an area of higher
  concentration to an area of lower concentration.
• Also a type of passive transport since water
  moves down the concentration gradient and the
  cell does not expend energy.
• Direction of Osmosis net direction depends on
  relative concentrations of solutes on the two
  sides of the membrane.

10

• Difussion of water and dissolved substances
  animation

Animation
11
Hypotonic

• When the concentration of solute molecules
  outside is lower than inside ? water diffuses
  into the cell until equilibrium is established.
• Animation
• Another animation

12
Hypertonic

• When the concentration of solute molecules
  outside the cell is higher than inside ? water
  diffuses out of the cell until equilibrium
  occurs.
• animation

Animation
13
Isotonic

• When concentration of solutes inside and outside
  are equal ? water diffuses in and out at equal
  rates. No net movement.
• All three situations -- animation

14
Animation and quiz
15
How Cells Deal with Osmosis

• Isotonic environment no difficulty keeping
  movement of water balanced.

16
How Cells Deal with Osmosis

• Hypotonic environment require relatively lower
  water concentrations in cytosol to function
  normally, so they must rid themselves of excess
  water that is entering by osmosis.

17
Examples of Hypotonic Environment

• Paramecium use contractile vacuoles, organelles
  that remove water from a cell with a
  pumping/contracting action that requires the cell
  to expend energy.

18

• Other organisms pump solutes out of the cytosol.
  Lowering the solute concentrations in the cytosol
  bringing it closer to the concentrations in the
  environment so less water diffuses in.

19

• Plant roots are surrounded by water which moves
  in by osmosis. The cells swell until the membrane
  presses against the inside of the cell wall and
  is called Turgor pressure.

20

• Cytolysis the bursting of a cell due to too much
  water entering by osmosis

21
How Cells Deal with Osmosis

• Hypertonic environment Water leaves the cell
  through osmosis.
• Plasmolysis turgor pressure is lost when water
  leaves the cell. Cells shrink away from cell
  walls. (Plants wilt if they dont receive enough
  water.)

22
Facilitated Diffusion

• Type of passive transport used for molecules that
  cannot diffuse rapidly through cell membranes
  even when a concentration gradient exists.

23
Facilitated Diffusion

• Movement is assisted by carrier proteins in the
  membrane which transport molecules from areas of
  higher concentration on one side to areas of
  lower concentration on the other side.
• Still considered passive transport because
  molecules are moving down the concentration
  gradient and the cell does not supply additional
  energy

24
Facilitated Diffusion

• Model Carrier protein binds to molecule and
  changes shape, shielding the molecule from the
  hydrophobic interior of the lipid bilayer.
  Releases molecule on the other side and returns
  to original shape.
• Example Glucose is too large to diffuse so
  carrier proteins help out.

25
(No Transcript)
26
Facilitated Diffusion

• Facilitated diffusion can help move substances in
  or out depending on the gradient.
• Carrier proteins are each specific for one type
  of molecule
• Facilitated Diffusion Animation and Quiz

27
(No Transcript)
28
Diffusion through Ion Channels

• Type of passive transport that involves membrane
  proteins known as ion channels sodium (Na),
  potassium (K), calcium (Ca2), chloride (Cl-)
• Ion channels provide small passageways through
  which ions can diffuse. Each types of channel is
  specific for one type of ion.
• Some are always open, others have gates which
  open and close in response to stimuli (stretching
  of cell membrane, electrical signals, chemicals
  in cytosol or external environment)

29
Gated Ion Channels
30
Animation Review of all types of passive
transport
31
Active Transport
32
Types of Transport

• Passive Transport
• Diffusion
• Osmosis
• Facilitated Diffusion
• Diffusion through Ion Channels
• Active Transport
• Cell Membrane Pumps
• Endocytosis
• Exocytosis

33
Active Transport

• Movement of materials up their concentration
  gradient from an area of lower concentration to
  an area of higher concentration and requires a
  cell to expend energy

34
Cell Membrane Pumps

• Carrier proteins that move substances up
  gradients. Similar to facilitated diffusion but
  goes up in concentration instead of down.
• Sodium-Potassium Pump Na/K
• To function normally, many types of animal cells
  must have higher Na outside and higher K inside
• Creates an electrical gradient across the cell
  membrane. Outside becomes and inside becomes
  like a battery. Important in conduction of
  electrical impulses along nerve cells.

35
(No Transcript)
36

• Sodium Potassium Pump animation

37
Endocytosis and Exocytosis

• For macromolecules and food particles too large
  for other transport.
• Also used to transport large quantities of small
  molecules at one time.
• Requires cells to expend energy so it is
  considered active transport.

38
Endocytosis

• Process by which cells ingest external fluid,
  macromolecules and large particles including
  other cells.
• External materials are enclosed by a portion of
  the cell that folds in on itself, pinches off and
  forms a membrane-bound organelle called a
  vesicle.
• Some vesicles fuse with lysosomes and their
  contents are digested by enzymes. Others fuse
  with other organelles.

39
Types of Endocytosis

• Pinocytosis take in solutes or fluids
• Phagocytosis take in large particles or whole
  cells.
• Many unicellular organisms feed this way.
• Animal cells use this to ingest harmful bacteria
  or viruses.
• Phagocytes are cells that ingest bacteria and
  virus and fuse with lysosomes that destroy them.

Animation endocytosis
40
Endocytosis
Animation w/ sound
41
Exocytosis

• Essentially the reverse of endocytosis.
• Vesicle fuses with cell membrane and releases
  contents into the environment.
• Used to release large molecules such as proteins
  (made by ribosomes and packaged into vesicles by
  the golgi apparatus)
• Cells in the nervous and endocrine systems use it
  to release small molecules that control the
  activities of other cells.

42
Exocytosis
43
(No Transcript)