Transport of materials across the cell membrane Packet 5 part 2

What is a concentration gradient? An increase or decrease in the density of a type of molecule in a given area. Which way will the molecules move?

Molecules naturally spread out with their kinetic energy.

Molecules move from high to low concentration naturally Diffusion Molecules move down their concentration gradients.

Osmosis Water is very important, so we talk about water separately Osmosis –diffusion of water from HIGH concentration of water to LOW concentration of water across a semi-permeable membrane

Passive Transport: Simple Diffusion Move from HIGH to LOW concentration No energy required inside cell outside cell Which way will fat move? fat LOW HIGH

Crossing the cell membrane What molecules can get through the cell membrane directly with simple diffusion? –Small lipids (fatty acids, glycerol) can pass directly through –small uncharged molecules like O 2, CO 2 and H 2 O (**) can also pass directly through inside cell outside cell Fatty acid salt aa H2OH2O sugar waste but… what about other stuff? O2O2 CO 2

Protein channels Proteins act as doors in the membrane –channels to allow specific molecules through cell membrane

Facilitated Diffusion Move from HIGH to LOW through a protein channel inside cell outside cell sugar Which way will sugar move? sugar LOW HIGH

Diffusion Summary Move from HIGH to LOW concentration –directly through membrane simple diffusion no energy needed –help through a protein channel facilitated diffusion (with help) no energy needed HIGH LOW

Active transport Cells may need molecules to move against concentration gradient –need to pump “uphill” from LOW to HIGH using energy –protein pump (transport protein) –requires energy ATP

Figure 8.19 The three types of endocytosis in animal cells RME

Transport summary simple diffusion facilitated diffusion active transport ATP No energy needed High to low concentration energy needed Low to high concentration Against the concentration gradient: swimming against the current With the concentration gradient: Floating downstream

Tonicity

Keeping water balance Cell survival depends on balancing water uptake & water loss Tonicity= the relative amount of dissolved solutes in an aqueous solution freshwater balanced saltwater

Keeping water balance A hypotonic solution has a concentration of solutes that is lower than inside the cell. A hypertonic solution has a concentration of solutes that is higher than inside the cell. An isotonic solution has a concentration of solutes that is equal to the concentration inside the cell.

Solutions and osmosis Remember, water will diffuse from an area of high concentration to an area of low concentration. HypotonicHypertonic Less solute, more water More solute, less water Isotonic The net movement is now equal. The net movement is from the left side to the right side.