Cell Transport Cell membrane All cell are surrounded
Cell Transport
Cell membrane • All cell are surrounded by a flexible cell membrane • It controls what enter and leaves the cell (gatekeeper) • It is made of 2 layers of lipids = lipid bilayer
• proteins are embedded within the lipid bilayer--act as channels or pumps to help get things across the membrane • Carbohydrates also attach, acting as signal receptors from other cells
Cell wall • Plant cells also have a strong, rigid layer around the membrane = cell wall • Is for support and protection of the cell • Other than plants, algae, fungi, and prokaryotes have walls.
concentration • The cytoplasm of the cell is a solution of water with many substances dissolved with in it • Concentration refers to the amount of solute within the solution
Diffusion • Particles constantly move and will spread out • Particles will move from areas where they are more concentrated (crowded) to areas of lower concentration (less crowded) • Diffusion – process of particles moving from high to low concentration
Diffusion across membrane • If there is more of a solute on one side of the membrane, the substance will move to the side of lower concentration to “spread out”
equilibrium • When the concentration is the same on both sides of the membrane, it has reached equilibrium. • Particles then move in equal directions. (*never STOP moving!)
Diffusion of O 2 into cell
Osmosis terms • permeable-can cross the membrane • impermeable-can not cross the membrane
• Osmosis is the diffusion of water molecules across the membrane. • (water will move from HIGH to LOW concentration)
• There is more sugar on right side, so amount of water on right is less • Sugar cannot pass, but the water can
• Water will move until the concentration of the solute “sugar” is equal • The two solutions are then isotonic – same strength
• The side with the higher concentration of solute = hypertonic- above strength • The side with the lower concentration of solute= hypotonic – below strength
Affect on cells • Cells must balance the movement of water from osmosis • Too much water in or out of cell will kill cell • Animal cells need an isotonic environment
Osmotic pressure • Unicellular organisms have “pumps” on membrane-contractile vacuoles • Many have walls to prevent bursting • Cells with walls like a hypotonic environment
Facilitated diffusion • When Proteins on the membrane act as channels to help (facilitate) some molecules get across, (but still is G to L). • Still G to L, so NO ENERGY NEEDED!
Active transport • Cells must sometimes move materials in the opposite direction of diffusion- against the concentration gradient = active transport • Requires energy (LESS TO GREATER!) • Proteins in the membrane can act as ‘pumps’
Active transport ATP= cell energy
Sodium potassium pump Most used pump in animals! ATP is used to do it.
• Larger material may need to be transported by movements of the cytoplasm itself • Endocytosis – taking material into the cell by folds/pockets formed in the membrane (like pacman) • The pocket then breaks loose from the membrane and is a vacuole • Uses energy
Endocytosis (2 types) phagocytosis pinocytosis • Material taken in is of solid nature • Cell is “eating’ • Material taken in is liquid
exocytosis • Vacuole fuses with cell membrane pushing contents OUT of the cell (like cell vomiting!)
SUMMARY: 1. PASSIVE TRANSPORT (G to L) no energy A. Diffusion B. Osmosis C. Facilitated Diffusion 2. ACTIVE TRANSPORT (uses energy) A. Proteins act as pumps (L to G) B. Endocytosis (phagocytosis/pinocytosis) C. Exocytosis http: //www. bozemanscience. com/016 -transport-across-cellmembranes/
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