Cell Function

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Cell Function Cells and their Environment

• Chapter 7, Section 3
• L2 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
  (down a concentration gradient).
• Continues until equilibrium is reached.

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Diffusion
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Concentration Gradient
100 - high number
0 - lower number
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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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LAB Diffusion
Dialysis tubing simulates a cell membrane
Starch Water glucose
Water Iodine
What will happen to the starch?
glucose? iodine ?
WHY?
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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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Facilitated Diffusion uses carrier proteins

• Carrier proteins in the membrane help the
  molecules across faster than would be expected by
  diffusion alone

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Facilitated Diffusion
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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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Hypertonic Solution More water inside cell than
outside
Plasmolysis
Plasmolysis
Cells shrink and die
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Iso-osmotic Solution same concentration of
water inside and outside cell
Animal cell
Plant cell
No net gain or loss of water
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Hypotonic Solution more water outside cell than
inside
Cytolysis cell swells and bursts
Builds up turgor pressure cell becomes stiff,
keeping plant upright
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Blood in different solutions
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Diffusion in an animal cell
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Osmosis
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Active Transport
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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