Key Ideas What determines the direction in which passive transport occurs? Why is osmosis important? How do substances move against their concentration gradients?

8-2 Cell Transport

Cell Transport Must move substances of varying size, electrical charge, and composition into and out of the cell 2 types of transport Passive Does not use energy Moves from a high concentration to a low concentration Active Requires energy Moves from a low concentration to a high concentration

Passive Transport- Terms Equilibrium Results when the concentration of a substance is the same through out a space Concentration The amount of a particular substance in a given volume Concentration gradient Occurs when one area has a higher concentration than another area does.

Passive Transport-Simple Diffusion The movement of particles from regions of higher density to regions of lower density across the cell membrane. The direction of movement depends on the concentration gradient and does not require energy.

Passive Transport-Simple Diffusion

Diffusion Facilitated Diffusion

Passive Transport Facilitated Diffusion Transport proteins Helps ions and polar molecules diffuse through the membrane 2 types Channel proteins or pores Carrier proteins

Passive Transport Facilitated Diffusion Channel proteins or pores Act as a tunnel through the membrane Allow specific ions, sugars, and polar molecules to pass Carrier Transports substances that fit within their binding site Results in changing the shape of the protein and the delivery of the substance to the other side of the cell

Passive Transport Facilitated Diffusion

Passive Transport: Osmosis the diffusion of water across a selectively permeable membrane Allows cells to maintain balance as their environment changes.

Passive Transport: Osmosis

Passive Transport: Osmosis Water Channels form of facilitated diffusion Polar water molecules must rely on channel proteins in the cell membrane that only allow water molecules to pass through.

Passive Transport: Osmosis Predicting Water Movement Hypertonic Water moves out Hypotonic Water moves in Isotonic Water diffuses in and out of the cell at an equal rate

Effects of Osmosis If left unchecked, the swelling caused by a hypotonic solution could cause a cell to burst. Ways to prevent the cell from bursting rigid cell walls of plants and fungi prevent the cells from expanding too much. many plants are healthiest in a hypotonic environment. Some unicellular eukaryotes have contractile vacuoles which collect excess water inside the cell and force the water out of the cell. Animal cells have neither cell walls nor contractile vacuoles. avoid swelling caused by osmosis by actively removing solutes from the cytoplasm.

Active Transport Review Requires energy Moves against the concentration gradient – move from low concentration to high concentration

Active Transport Pumps Requires carrier proteins Ex. sodium-potassium pump sodium ions bind to the carrier protein through the use of energy(ATP) changes shape releasing sodium to the outside of the membrane while open to the outside, potassium ions bind to the carrier protein when the pump returns to its original shape the potassium ions are released on the inside. For every 3 sodium ions taken out there are 2 potassium ions taken in

Active Transport Vesicles Allows proteins, polysaccharides, and other substances that are too large to be transported by carrier proteins Contain the same lipid bilayer as the membrane so vesicles can easily break off and fuse with the membrane 2 types Exocytosis Endocytosis

Endocytosis the movement of a large substance into a cell by means of a vesicle cell membrane folds inward creating a pouch for the substance to enter once in the pouch it pinches off and forms a vesicle these vesicles can fuse with lysosomes and other organelles

Active Transport

Exocytosis The movement of material out of the cell by the means of a vesicle Reverse process of Endocytosis Vesicles fuse with the cell membrane and releases its contents to the outside of the cell Used to export proteins modified by the golgi apparatus

Active Transport