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Cell Transport

Cell Transport. All cells must maintain HOMEOSTASIS (balance). What types of substances must be balanced in a cell?. First Step: Cell Membrane. Cell membrane is semi- or selectively permeable – not all molecules can pass through. Concentration gradient.

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Cell Transport

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  1. Cell Transport All cells must maintain HOMEOSTASIS (balance). What types of substances must be balanced in a cell?

  2. First Step: Cell Membrane • Cell membrane is semi- or selectively permeable – not all molecules can pass through.

  3. Concentration gradient • The difference in concentration of a given molecule between two points is called the concentration gradient. • The larger the gradient, the greater the net movement of the molecules. • Molecules continue to move until evenly distributed (gradient = 0).

  4. Diffusion • Diffusion occurs whenever molecules move from areas of high concentration to low concentration. • The movement is caused by the random kinetic energy of the molecules, so does not require any energy input.

  5. Passive Transport • Does not require energy. • Molecules move from high concentration to low concentration. • Three major types: • Simple Diffusion • Osmosis • Facilitated Diffusion

  6. Simple Diffusion across a Membrane • Molecules pass directly through lipid bilayer. • Molecules generally small with little or no electrical charge (O2, CO2, H2O, etc.).

  7. Facilitated Diffusion • Molecules move through special proteins. • Move from high concentration to low. • Does not require energy.

  8. Osmosis • Special type of diffusion. • Involves water moving across a selectively permeable membrane. • Very important in living organisms.

  9. Tonocity • During osmosis, water moves from high concentration to low concentration. • Water is called a solvent, molecules dissolved in water are called solutes. • There are three terms to describe the direction in which water molecules will move during osmosis: • Hypotonic • Isotonic • Hypertonic

  10. Hyper- and Hypotonic • Hypo = less solute • Hyper = more solute • These are relative terms like “greater than” or “less than” Water moleclue Solute molecule

  11. Effects of Tonicity on Cells

  12. Active Transport • Moves molecules against their gradient (from low to high concentration). • This requires energy. • Two major types: • Carrier Proteins • Endocytosis

  13. Carrier Proteins • Special membrane proteins that use energy to move molecules across the membrane.

  14. Endocytosis • Process by which large molecules or large volumes of liquid are taken into cells. • Endo- means inside, cytosis refers to cell • Phagocytosis = “cell eating” • Pinocytosis = “cell drinking” • Requires energy.

  15. Phagocytosis • Cell membrane folds around and brings particle into cell. • The membrane around the particle pinches off and forms a vesicle. • The vesicle will eventually fuse with a lysosome for digestion.

  16. Pinocytosis • Cell membrane folds around and brings liquid into cell. • The membrane around the liquid pinches off and forms a vesicle.

  17. Exocytosis • The opposite of endocytosis is called exocytosis (exo = outside). • This is what happens to the packages produced by the Golgi bodies that leave the cell. Cell Membrane

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