6 PASSIVE TRANSPORTAlways moves substances down a concentration gradient.It requires no energy expenditure on the part of the cell to move these substances across the membrane.
7 3 Kinds of Passive Transport: DiffusionOsmosisFacilitated Diffusion
8 DIFFUSIONDiffusion is the movement of a solute from an area of higher concentration to an area of lower concentration. When the solute is in equal concentration throughout, it is said to be in equilibrium. The molecules will continue to move, but there will be no net movement in one direction or another
9 OSMOSISWater moves by osmosis through a semipermeable membrane. Water will always move from an area of high water concentration to an area of low water concentration. Water’s tendency to move is called water potential (it has the potential to move). It is said to move from an area of higher water potential to an area of lower water potential.
10 OSMOSISSince it is the amount of solute that determines which way water moves, we could have 3 different sets of circumstances…a low amount of solutea high amount of solutean equal amount of solute on either side of the membrane. These 3 types of solutions have names
11 HYPOTONIC SOLUTIONSHypotonic solutions have less solute (more water) than the solution they are being compared to. Water always moves from a hypotonic solution into the solution containing the greater amount of solute.
12 HYPERTONIC SOLUTIONSSolutions that contain a greater amount of solute (less water) than the solution they are being compared to are called hypertonic. Water always moves from a hypotonic solution into a hypertonic solution
13 ISOTONIC SOLUTIONSWhen two solutions separated by a membrane contain equal amounts of solute, they are said to be isotonic to each other. Water will move back and forth between the solutions, but there will be no net movement in one direction or the other.
14 OSMOSISKeep in mind that to use the terms hypotonic, hypertonic, or isotonic, you must be comparing two solutions. These two solutions are on opposite sides of the plasma membrane.
15 Now let’s see what happens to a living cell placed in one of these three types of solutions. We will use a red blood cell (RBC) as an example of an animal cell.
17 Now let’s see what happens to a plant cell in our 3 types of solutions Now let’s see what happens to a plant cell in our 3 types of solutions. Why would a plant cell behave differently than an animal cell? Do you know?
18 PLANT CELLS IN HYPOTONIC SOLUTIONS Plant cells placed in a hypotonic solution will fill with water. They have a central vacuole that can take up to 90% of the space inside the cell. This is where the water goes. The plant will swell and the plasma membrane will push against the dead cell wall. The plant cell will not burst because of the cell wall. The rigid condition of the plant cell is known as turgor. The cell is said to be turgid
19 PLANT CELL IN HYPERTONIC SOLUTION Plant cells placed in a hypertonic solution will lose water from their central vacuole. The shrinking of the central vacuole will cause the plasma membrane to pull away from the dead cell wall (which is immovable). This is known as plasmolysis. The cell will plasmolyze
20 PLASMOLYSIS IN ELODEAPlasmolysis in Elodea. Note the shrinking of the cytoplasm and how the plasma membrane has pulled away from the cell wall.
26 CARRIER PROTEINAlternates between two conformations, moving a solute across the membrane as the shape of the protein changes. Can move solute in either direction. Specific for certain solutes.
27 Active TransportRequires use of a carrier protein (like facilitated diffusion)However, Active Transport moves solutes against the concentration gradient from low to high concentrationRequires cell to expend energy in the form of ATPSymports carry 2 different molecules in the same direction, while antiports carry two different molecules in opposite directions
29 SODIUM-POTASSIUM PUMP The sodium-potassium (NaK) pump is the classic example of active transport. It uses an antiport carrier protein to move Na (which is INa) outside and bring K (which is Outside OK) in. The NaK pump is used in nerve conduction and muscle contraction
30 ION PUMPS Ion pumps are another example of Active Transport H+ ions (protons) are pumped to one side of a membrane by active transport creating a proton gradient. This gives the protons potential energyThis energy can be used to do work including a type of cellular transport called co-transport
32 BULK TRANSPORT Transport Of Large Molecules Into or Out of the Cell Involves the use of vesiclesEndocytosis – into cellExocytosis – out of the cellCell must use ENERGY (ATP)
33 EXOCYTOSISMovement of large substances out of the cellRequires ATP
34 ENDOCYTOSISEndocytosis is the process of bringing large molecules into the cell. There are 3 types of endocytosis: phagocytosis, pinocytosis, and receptor-mediated endocytosis.
35 PHAGOCYTOSIS – “Cell Eating” Phagocytes are cells that “eat” other cells. White blood cells are phagocytes that patrol the body looking for invaders, such as bacteria, to ingest. Once inside the cell, the invader is broken down into its component molecules.
36 PINOCYTOSIS – “Cell Drinking” Pinocytosis moves liquids and smaller particles into the cell