Cell Transport Different Methods used by Cells to Move Molecules into or out of the Cell

Active vs. Passive Transport The different methods of moving molecules across membranes can be divided into two groups, depending on whether they require energy or not. Active Transport will not happen unless the cell uses energy to move the molecule. Passive Transport happens automatically without needing energy. Atp 4 NRG!!!

Concentration Gradients The concentration of a liquid describes the amount of a substance dissolved in it. “Solvent” = liquid that has molecules dissolved in it Low Concentration High Concentration “Solute” = molecule dissolved in a liquid A gradient describes the difference between two things – so the concentration gradient is the amount of difference in the concentration inside and outside of the cell.

Inside Cell Outside Cell Cell Membrane Both diagrams show the inside of the cell has fewer dissolved molecules than the outside Greater Concentration Gradient Top diagram has a bigger difference between the inside and outside of the cell Lesser Concentration Gradient Inside Cell Outside Cell Cell Membrane

Hypotonic vs. Hypertonic If molecules are more concentrated inside the cell than outside, we say that the cell is in a hypotonic solution (“hypo” means low). If molecules are more concentrated outside the cell than inside, we say the cell is in a hypertonic solution (“hyper” means high). Cell in a hypotonic solution Cell in a hypertonic solution

Gradients & Energy Molecules “want” to equalize concentrations inside and outside the cell. If they can equal out by moving from high to low concentration (“downhill”), no energy is required and passive transport occurs. If they need to move from low to high concentration to equal out, energy is required and active transport is needed to move the molecules “uphill” against the concentration gradient.

No energy needed to move from high to low – passive transport Outside Cell Inside Cell Energy required to move from low to high – active transport

Types of Passive Transport Diffusion: molecules just cross the membrane from high to low concentration. They must be small enough to squeeze between the phospholipids, like oxygen & CO2. Facilitated Diffusion: molecules cross from high to low, but they are too big to squeeze through, so they need help from a channel protein. Osmosis: water moves across the membrane from high H2O to low H2O concentration. This is tricky because the H2O concentration is the opposite of the molecule’s concentrations!

2% sugar solution (Low concentration) 98% water Osmosis 2% sugar solution (Low concentration) 98% water 5% sugar solution (High concentration) 95% water What happens to a cell in these two solutions if the cell has 3% sugar?

Osmosis cell = 3% sugar 97% water 5% sugar solution (High concentration) 95% water Hypertonic solution 2% sugar solution (Low concentration) 98% water Hypotonic solution cell = 3% sugar 97% water Water enters cell by osmosis & cell swells up Water exits cell by osmosis & cell shrinks

Types of Active Transport Active transport usually refers to the cell using energy from ATP to power a carrier protein that moves molecules in or out. Exocytosis is when the golgi bodies use vesicles to send molecules out of the cell. Endocytosis is when a cell wraps its membrane around a particle and “swallows” it into a vacuole. If it is a large particle, it is called phagocytosis (cellular eating), if it is a small particle it is called pinocytosis (cellular drinking)

Exocytosis

Endocytosis