Chapter 5: Homeostasis & Transport

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Chapter 5Homeostasis Transport
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DIFFUSION/OSMOSIS

• MOVEMENT OF MATERIALS THROUGH THE CELL MEMBRANE

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Cell membrane

• helps maintain homeostasis by controlling what
  enters or leave cells.
• Homeostasis (maintaining stability)
• It is selectively permeable, only allowing
  certain molecules to pass through.

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Passive Transport

• Some substances can cross the cell membrane
  without any input of energy by the cell.
• The movement of such substances across the
  membrane is known as passive transport

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• To stay alive, a cell must exchange materials
  such as food, water, wastes w/its envt.
• Small molecules like water can move in and out
  freely but large molecules cannot.

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Diffusion

• the movement of molecules from an area of higher
  concentration to an area of lower conc.
• HIGHER ? lower
• Diffusion is a type of passive transport because
  it does not require energy
• The difference in the conc. of molecules across a
  membrane is called a concentration gradient

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Increasing rate of diffusion

• Concentration
• (ammonia)
• Pressure
• (spray can)
• Temperature
• (water boiling molecules move faster)

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Solutions

• Solutions mixture of 2 or more substances
  dissolved together.
• Example Salt water
• Solute - substance that is dissolved (salt)
• Solvent - subst. the solute is dissolved in
  (water)
• Water serves as the main solvent in living things

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equilibrium

• Diffusion continues until conc. is the same on
  both sides of a membrane
• When a conc. gradient no longer exists,
  equilibrium has been reached BUT molecules will
  continue to move equally back forth across a
  membrane.
• There is always movement back forth across a
  membrane.

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Types of Solutions

• Hypertonic
• Hypotonic
• Isotonic

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Hypertonic Solution

• Solute conc. outside the cell is higher
• (less H2O outside)
• H2O diffuses out of the cell until equilibrium is
  reached
• Cells shrink die if too much H2O is lost
• Plant cells become flaccid (wilt) called
  plasmolysis

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Hypotonic Solution

• Solute conc. inside the cell is higher
• (less H2O inside)
• H2O moves into the cell until equilibrium is
  reached

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• Animal cells swell burst if they take in too
  much H2O, called Cytolysis
• Plant cells become stiff or firm due to H2O
  pressing against the cell wall.
• Turgor pressure in plant cells helps them keep
  their shape

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Isotonic Solutions

• Conc. of solutes same inside outside the cell
• H2O moves into out of cell at an equal rate

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OSMOSIS

• Osmosis is the diffusion of H2O.
• Diffusion of H2O from an area of higher conc.
  (less solute) to an area of lower conc. (more
  solute)

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How do we deal w/osmosis?

• The cells of land animals are usually in isotonic
  envt (equilibrium)
• Freshwater organisms live in hypotonic envt so
  H2O constantly moves into their cells
• Unicellular freshwater organisms use energy to
  pump out excess H2O by contractile vacuoles.
• Cell walls prevent plant cells from bursting in
  hypotonic envt
• Some marine organisms can pump out excess salt

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Facilitated Diffusion

• Involves carrier proteins embedded in a cells
  membrane to help move molecules across a membrane.

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Active Transport

• Movement of molecules across a cell membr. using
  energy.
• Molecules are transported against their
  concentration gradient from an area of lower to
  higher concentration (opposite of diffusion.)

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Example

• Plants use active transport to help roots absorb
  nutrients from the soil (plant nutrients are more
  conc. inside the root than outside)

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Movement of LARGER molecules

• ENDOCYTOSIS cell takes in large molecules
• Cell engulfs molecules too large to pass through
  the membrane naturally.
• Folds or pockets swallow the molecules
• PHAGOCYTOSIS cell takes in lg. solids (food)
• PINOSCYTOSIS liquids (water)
• EXOCYTOSIS movement of large molecules OUT of
  the cell.

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THE END