movement through cell membranes n.
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Movement through cell membranes. Diffusion. Example: exchange of oxygen and carbon dioxide in lungs Molecules or ions moving from areas of higher concentration to lower concentration Difference in concentration is the concentration gradient Concentrations are equal = equilibrium.

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diffusion
Diffusion
  • Example: exchange of oxygen and carbon dioxide in lungs
  • Molecules or ions moving from areas of higher concentration to lower concentration
  • Difference in concentration is the concentration gradient
  • Concentrations are equal = equilibrium
diffusion in out of a cell
Diffusion in & out of a cell

1. the cell membrane is permeable to that substance

2. concentration gradient exists such that the substance is at a higher concentration either outside or inside the cell.

diffusion in out of a cell example
Diffusion in & out of a cellexample
  • Intracellular Oxygen is always low b/c it is constantly used during metabolism; extracellular oxygen is high due to homeostatic mechanisms. Concentration gradient always favors oxygen diffusing into the cell.
  • CO2 is a waste product of metabolism, and thus is high inside cells; homeostasis maintains lower levels of CO2 outside the cell. Concentration gradient always favors CO2 to diffuse out of the cell.
  • Thus – never an equilibrium between CO2 and O2
facilitated diffusion
Facilitated Diffusion
  • Substances not able to pass through the lipid bilayer need help from membrane proteins
  • Examples: glucose and amino acids
  • Glucose needs insulin to help it diffuse through membranes of certain cells.
slide7
Example: distilled water entering the cell
  • Water molecules diffuse fromhigher water concentrations to lower water concentrations
  • In solutions: higher concentration of solute, lower concentration of water; lower concentration of solute, higher concentration of water.
slide8
Greater the concentration of solute (proteins), lower water concentration, greater osmotic pressure.
  • Lower the concentration of solute (proteins), higher water concentration, lower osmotic pressure
osmotic pressure
Osmotic Pressure
  • When intracellular and extracellular fluids and pressure are the same = isotonic
  • When extracellular fluid has greater pressure than intracellular – water leaves cell = hypertonic
  • When intracellular fluid has greater pressure than extracellular – water enters cell = hypotonic
filtration
Filtration
  • Forced movement of molecules through membranes
  • Separate solids from water
  • Tissue fluid forms when water and small dissolved substances are forced out through thin porous walls of blood capillaries, but larger particles are left
  • Force of this movement comes from blood pressure, generated by a higher pressure inside the heart, less pressure outside the heart.
active transport
Active Transport
  • Similar to facilitated diffusion
  • Differs in that particles are moving from areas of low concentration to high concentration
  • Carrier proteins also called pumps
  • Examples: sugars, amino acids; sodium, potassium, calcium, and hydrogen ions
  • Also absorb nutrients into cells of the intestinal walls
endocytosis
Endocytosis
  • Molecules or other particles that are too large to enter a cell by diffusion, facilitated diffusion or active transport.
  • Three types
    • Phagocytosis: cell eating, takes in solids, ie. Bacteria
    • Pinocytosis: cell drinking, takes in tiny droplets, ie. Water
    • Receptor-mediated endocytosis: moves specific particles into the cell, particle binds to a receptor site protein.
exocytosis
Reverse process of endocytosis

Cell secretes a substance stored in vesicle

ie. Neurons – release neurotransmitters that signal nerves, muscles, or glands

Exocytosis