Homeostasis and Transport

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Homeostasis and Transport

• Section 1 Passive Transport
• Section 2 Active Transport

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Passive Transport

• Diffusion
• Concentration gradient
• Equilibrium
• Osmosis
• Hypotonic
• Hypertonic
• isotonic

• Contractile vacuoles
• Turgor pressure
• Plasmolysis
• Cytolysis
• Facilitated diffusion
• Carrier proteins
• Ion channels

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DIFFUSION

• diffusion is the movement of molecules from an
  area of higher concentration to an area of lower
  concentration, driven by the molecules kinetic
  energy.
• It eventually reaches equilibrium, a condition in
  which the concentration of the molecules is the
  same throughout a space or on both sides of a
  membrane.

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• Molecules can diffuse across a cell membrane by
  dissolving in the lipid bilayer or by passing
  through pores in the membrane.

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OSMOSIS

• Osmosis is diffusion of water across a membrane.
  The net direction of osmosis is determined by the
  relative solute concentrations on the two sides
  of the membrane.
• What the heck does that mean???????

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• You see if the solute concentration outside the
  cell is LOWER than that inside the cell, the
  solution outside is said to be HYPOTONIC.
• Hypotonic Water diffuses INTO the cell.
• If the solute concentration outside the cell is
  HIGHER than that inside the cell, the solution
  outside is said to HYPERTONIC.
• Hypertonic Water diffuses OUT of the cell.
• Isotonic at equilibrium

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SOLUTES

• What are the solute molecules?
• Oxygen, carbon dioxide, nitrogen, benzene,
  glycerol, ethanol, amino acids, glucose,
  nucleotides,
• Ions hydrogen, sodium, potassium, calcium,
  chlorine, magnesium,..etc..

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Normal blood cells look like this below. The
solution is isotonic, or in equilibrium. The
prefix iso- means the same.
The blood cells swell up if they are in a
solution that is hypotonic. Water is diffusing
into the cells. Eventually they will burst. The
prefix hypo- means less than or below.
In this case, the cells are shriveling up. They
are in a hypertonic solution. The water is
diffusing out of the cell. The prefix hyper-
means above or more than.
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Hypotonic, Hypertonic, Isotonic
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How cells deal with Osmosis

• Animal cells have ions pumps embedded in the cell
  membrane

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How cells deal with Osmosis

• Plant cells live in a hypotonic environment.
  Water, therefore, moves by osmosis into the plant
  cell, which swell as they fill with water. The
  swelling stops when the cell membrane presses
  against the inside of the cell wall. This
  pressure is called turgor pressure. This pressure
  helps keep a plant upright.

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How cells deal with Osmosis

• Protozoans eject water through a specialized
  organelle called a contractile vacuole.

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OSMOTIC SWELLING

• Three ways in which cells avoid osmotic swelling.
• The animal cell keeps the intracellular solute
  concentration low by pumping out ions.
• The plant cell is saved from swelling and
  bursting by its tough cell wall.
• The protozoan avoids swelling by periodically
  ejecting water that moves into the cell.