Diffusion and Osmosis: How does stuff get into and out of a cell?

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Diffusion and Osmosis How does stuff get into
and out of a cell?

• The Cell in its Environment
• Ch 7, Section 2
• L3 Biology

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Molecules are always moving

• Molecules move randomly and bump into each other
  and other barriers

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Diffusion

• Movement of molecules from an area of high
  concentration to an area of lower concentration
• Continues until equilibrium is reached.

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Diffusion
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Diffusion

• Occurs without control or energy use it is
  called Passive Transport
• Affected by
• Size of molecules
• Size of pores in a membrane
• Temperature
• Stirring

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Simple Diffusion
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Cell Membranes are Semipermeable

• Let some molecules pass through and not others.
• Small molecules pass through ex water
• Large molecules cant pass through ex proteins
  and complex carbohydrates

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Which molecules will diffuse?
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How long does diffusion continue?

• Until equilibrium is reached
• This means there will be an equal distribution of
  molecules throughout the space this is why
  odors smell strong at first, then seem to
  disappear

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Osmosis A Special kind of Diffusion

• Diffusion of water across a selectively permeable
  membrane
• Cytoplasm is a solution of water and solutes
  (stuff dissolved in the water).
• Water moves into and out of cells because of the
  different concentrations of the solutes.
• Different kinds of cells react differently to
  osmosis, depending on the solution they are in

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Blood in different solutions
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Active Transport uses carrier molecules to move
molecules from an area of lower concentration to
an area of higher concentration
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Endocytosis

• Very large molecules or substances must enter the
  cell by the membrane pinching inward

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Pinocytosis

• The cell takes in liquid droplets and forms a
  vacuole

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Phagocytosis

• The cell takes in large particles

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Exocytosis

• The cell gets rid of secretions or wastes

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Phagocytosis in action phagocyte (white blood
cell) going after a bacteria cell
The End