cellular transport. diffusion maintaining homeostasis – cell membranes help organisms maintain...
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Cellular Transport
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Diffusion• Maintaining
homeostasis– Cell membranes help
organisms maintain homeostasis by controlling what substances may enter or leave cells.
– Passive Transport- substances can cross the cell membrane without any input of energy
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• Diffusion–Molecular motion•Molecules are in constant motion
because they have kinetic energy (brownian motion)•Molecular motion is random•Molecules tend to move from areas
where they are more concentrated to areas where they are less concentrated
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• Diffusion- movement of molecules from area of higher concentration to area of lower concentration– Concentration gradient- difference in the
concentration of molecules across a distance– So, molecules tend to move “down” their
concentration gradient– Diffusion will eventually cause the molecules to be
in equilibrium– Equilibrium- concentration of molecules will be
the same throughout the space the molecules occupy
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• Diffusion– Simple diffusion- diffusion of substances across
the cell membrane without the help of membrane proteins
– Facilitated diffusion- the movememt of molecules across the cell membrane is assissted by specific proteins in the membrane• Used to move large molecules, polar molecules, ions• Carrier proteins- used in facilitated diffusion
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Osmosis• Osmosis- the process by which water
moleucles diffuse across a cell membrane from high to low concentration
• Form of passive transport (does not requir energy)
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• Direction of Osmosis–Depends on relative concentration of solutes on
the two sides of the membrane• Hypotonic- describes solution with solute
concentration lower than concentration inside cell (water diffuses in)• Hypertonic- describes solution with solute
concentration higher than concentration in cell (water diffuses out)• Isotonic- describes solution with solute
concentration equal to concentration in cell (water diffuses in and out at same rate)
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• How osmosis affects living cells
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Active transport• Active transport- when cells move materials
from area of lower concentration to an area of higher concentration, “against” the concentration gradient (requires energy, ATP)
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• Cell membrane pumps– Carrier proteins – “pumps”- moving from low to
high concentration– Sodium-potassium pump- transports Na+ ions and
K+ ions up their concentration gradient• Helps create electrical impulses that are important in
animal cells (nerve cells)
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• Movement in vesicles– Endocytosis- process by which cells ingest external
fluid, macromolecules, and large particles, including other cells by forming a vesicle• Pinocytosis- involves transport of solutes or fluids• Phagocytosis- movement of large particles or cells
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• Exocytosis- process by which a substance is released from the cell through a vesicle