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Notes: Cell membrane and the Cell Environment: Cells must maintain a biological balance with its environment to survive. To do this cells achieve homeostasis by controlling and regulating what gets into and out of the cell. There can be limits on how much the cell can adjust. Understanding how molecules move, what states of environmental conditions they exist best in and how far they are wiling to adjust determines how efficient cells are. Molecules travel in constant motion. As molecules travel they tend to move into areas where the molecules are less concentrated. This tells us the direction of the movement. PASSIVE TRANSPORT When direction of molecules moves from areas of high concentration to areas of low concentration this is called passive transport. Passive transport requires no need of energy to move the molecules . This also means it is moving from greater concentration to lesser concentration. The difference in concentration of a substance across space is called a concentration gradient. There are 3 types of passive movement. 1. Diffusion 2. Facilitated Diffusion 3. Osmosis Carrier Molecules= help transport molecules across the cell membrane. Carrier molecules are embedded in the membrane and some are extended across the membrane. Each carrier molecule is specialized to allow the movement of only one type of molecules across the membrane Gated channels- are also a form of passive transport that occurs when proteins in the membrane form a gated channel across the cell membrane and this allows the membrane to be permeable as needed. Again these gated channels are active in nerve impulses and contraction of muscles. Diffusion – is molecules spreading out across a concentration gradient from an area of high to low concentration. The example is the movement of oxygen across the cell membrane. Some kinds of molecules can diffuse across a membrane. The ability of a molecule to pass through a membrane depends on the sixe and type of molecule and the molecular structure of the membrane. Membranes that let some substances through are called selectively permeable membranes or semipermeable. If they are semipermeable they regulate what gets into and out of a cell. Facilitated diffusion-These are carrier molecules that transport molecules across the cell membrane without energy. Carrier molecules speed up diffusion rate. Ex: glucose which is to large to pass on its own needs the help of a carrier molecules. Osmosis- is the movement of water from an area of high concentration to an area of low concentration. So we say diffusion of water. The movement of water depends on the concentration of solutes in the solution or water. Water will diffuse or move to the area where the solutes are. Direction of Osmosis: Conditions Environment solution outside is in Hypotonic: Hypo means low Cell solution is Water will move Hypertonic Hyper means high Into the cell If the solute concentration in the environment is higher than in the cell Hypertonic Hypotonic Out of the cell If the solute concentration in the environment is equal to that in the cell Isotonic Iso means equal Isotonic No movement water will not move.. If the solute concentration in the environment outside the cell is lower than that in the cell Hypotonic solution exists in a coexisting hypertonic solution. Isotonic solution exists in a coexisting isotonic solution. If a plant cell swells s it fills with water it will not swell endlessly, because it is restricted by cell walls. When water pressure increases it is called turgor pressure. This pressure forces the cytoplasm and the cell membrane against the cell wall and the cell becomes rigid. ACTIVE TRANSPORT Active transport – is the movement of any substance across a cell membrane with the use of chemical energy. Materials will cross the cell membrane by either passive or active transport, depending on the size and chemical makeup of the material. The structure of the cell membrane also plays an important roll in both types of transport. Cell Membrane- consists of 2 layers, each layer containing lipid molecules. This is known as the lipid bilayer. The outside surface of the membrane is hydrophilic. (not afraid of water). The inside layer of the membrane is hydrophobic. (Afraid of water) This particular arrangement ensures that molecules that dissolve in water do not automatically pass through the membranes. A layer of lipids separates the 2 aquatic environments, one of the cell and one of the environments. Carrier molecules also can act and function in the active transport of molecules across the cell membrane. One type of active transport system is sodium-potassium pump. This is a mechanism that moves sodium ions out of the cell and forces potassium ions into the cell. Movement in both cases is against the concentration gradient, hence the reason it is active transport. This process depends on the ability of the protein carrier molecule to change shape. 3 Na ions fit into a carrier molecule. A chemical reaction using high-energy ATP molecules changes the shape fo the carrier molecule which causes the sodium to be released outside the cell. This pump is essential to all animal muscle and nerve contractions. When large molecules (food and waste) are too large to pass through the cell membrane the processes of endocytosis and exocytosis will enable particles to enter and exit the cell membrane. These processes are part of the cells maintenance of homeostasis to stay in balance with their environment by taking in nutrients, exporting proteins, and excreting wastes. Endocytosis- is the process y which cells engulf substances that are much too large to enter the cell by passing through the membrane. The large molecule outside the cell are enclosed by a portion of the cell, which folds into itself and makes a pouch called a vesicle, which pinches off from the membrane and enters the cytoplasm. There are two types of endocytosis- pinocytosis and phagocytosis. These two types of active transport engulf liquids; (pinocytosis) and engulf solids; (Phagocytosis) Exocytosis-helps the cell maintain homeostasis by exporting larger molecules out of the cell. Ex: the ribosomes make the proteins that the Golgi processes prepares and packages that move to the cell membrane. The vesicle membrane fuses with the cell membrane and dumps its contents out of the cell. Diversity of Cellular Life: All living things are composed of cells, use the same basic chemistry, follow the same genetic code, and even contain the same kinds of organelles. A single celled organism is also called a unicellular organism. Unicellular organisms grow, respond to the environment, transform energy, and reproduce. The also dominate life on earth. Multicellular organisms are made up of many cells. All multicellular organisms depend on communication and cooperation among specialized cells. Cells throughout an organism can develop in different ways to perform different tasks. This is called cell specialization.