Homeostasis and Cell Transport

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Homeostasis and Cell Transport

• Chapter 5

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Homeostasis

• The steady-state physiological condition of the
  cell or body.

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Cellular Transport
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Passive Transport
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Diffusion
impermeable
Semi-permeable

• The movement of particles from an area of high
  concentration to an area of low concentration.
• concentration gradient formed by the
  concentration of molecules at various points
  between the high and low areas.

permeable
Equilibrium the concentration of molecules will
be the same throughout the space the molecules
occupy.
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Osmosis

• The movement of water molecules across a
  selectively permeable membrane. Water moves from
  a region of high concentration to one of low conc.

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Hypotonic

• When the concentration of solute molecules
  outside the cell is lower than the concentration
  in the cytosol.
• Water diffuses into the cell until equilibrium is
  established.

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Hypertonic

• When the concentration of solute molecules
  outside the cell is higher than the concentration
  in the cytosol.
• Water diffuses out of the cell until equilibrium
  is established.

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Isotonic

• When the concentration of solutes outside and
  inside the cell are equal.
• Water diffuses into and out of the cell at equal
  rates, so there is no net movement of water.

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Contractile Vacuole

• Organelles in paramecia that collect excess water
  and then contract, pumping the water out of the
  cell.

Not a form of Passive Transport. Why?
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Turgor Pressure

• The pressure that water molecules exert against
  the cell wall.

Plasmolysis the shrinking of the cell membrane
of a plant cell in a hypertonic solution in
response to the loss of water by osmosis.
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Cytolysis

• The bursting of cells.

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Facilitated Diffusion

• The transport of substances through a cell
  membrane along a concentration gradient with the
  aid of carrier proteins.
• Carrier proteins proteins that transport
  substances across a membrane.

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Ion Channels

• Transport ions such as
• Sodium (Na)
• Potassium (K)
• Calcium (Ca)
• Chloride (Cl-)
• Not soluble in lipids
• Each type of ion channel is usually specific for
  one type of ion.
• Some ion channels are always open, some have
  gates.
• Gates may open or close in response to 3 types of
  stimuli streching of the cell membrane,
  electrical signals, or chemicals in the cytosol
  or external environment.

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Active Transport

• Energy in the form of ATP is used to move
  substances through the transport proteins.
  Substances can move across a membrane against
  concentration gradient.
• The carrier proteins involved are often called
  cell membrane pumps.

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Sodium-Potassium Pump

• Transports Na and K ions up the concentration
  gradient.
• At top speed, the pump can transport about 450
  Na ions and 300 K ions per second.
• The exchange of 3 Na ions for 2 K ions creates
  a positively charged environment outside the cell
  membrane and negatively charged inside the
  membrane.
• Important for the conduction of electrical
  impulses along nerve cells.

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Movement in Vesicles

• Endocytosis process by which cells ingest
  external fluid, macromolecules, and large
  particles, including other cells.
• External materials are enclosed by a portion of
  the cells membrane, which folds itself and forms
  a pouch.
• The pouch pinches off from the cell membrane and
  becomes a vesicle.
• Some vesicles fuse with lysosomes.
• 2 types
• pinocytosis
• phagocytosis

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Pinocytosis

• Involves the transport of solutes or fluid.

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Phagocytosis

• Movement of large particles or whole cells.
• Phagocytes cells in animals that use
  phagocytosis to ingest bacteria and viruses that
  invade the body.
• They fuse with lysosomes and enzymes then destroy
  the bacteria and viruses before they can harm the
  animal.

leukocytes
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Exocytosis
Process by which a substance is released from the
cell through a vesicle that transports the
substance to the cell membrane and then fuses
with the membrane to let the substance out of the
cell.
Proteins Waste Toxins