Cellular Transport PDF

# Cellular Transport ## Focus Question What processes enable substances to move into or out of a cell? ## Diffusion - **Particles are moving and colliding with each other in the air.** This happens because the particles in gases, liquids, and solids are in random motion. - **Substances dissolv...

# Cellular Transport ## Focus Question What processes enable substances to move into or out of a cell? ## Diffusion - **Particles are moving and colliding with each other in the air.** This happens because the particles in gases, liquids, and solids are in random motion. - **Substances dissolved in water move constantly in random motion called Brownian motion.** This random motion causes **diffusion**, which is the net movement of particles from an area where there are many particles of a substance to an area where there are fewer particles of the substance. - **The amount of a substance in a particular area is called concentration.** - **Substances diffuse from areas of high concentration to low concentration.** - **Diffusion does not require additional energy input** because the particles are already in motion. ## Diffusion across the Plasma Membrane - **In addition to water, cells need certain ions and small molecules.** Such as chloride ions and sugars to perform cellular functions. - **Water can diffuse across the plasma membrane.** - **Most other substances cannot.** - **Facilitated diffusion uses transport proteins to move other ions and small molecules across the plasma membrane.** ## Osmosis: Diffusion of Water - **The diffusion of water across a selectively permeable membrane is called osmosis.** - **Water molecules pass freely into and out of a cell through aquaporins.** - **Aquaporins are channel proteins embedded in the plasma membrane composed of tiny holes** that selectively allow small uncharged molecules, such as water to pass through. - **Regulating the movement of water across the plasma membrane is an important factor in maintaining homeostasis within the cell.** ### How osmosis works - **The concentration of a solution** decreases when the amount of solvent increases. A more concentrated solution has more solute than a less concentrated solution. ## Cells in an Isotonic Solution - **When a cell is in a solution that has the same Concentration of water and solutes**, it is said to be in an **isotonic solution.** - **Water still moves through,** but water enters and leaves the cell at the same rate. - **The cell is at Equilibrium** with the solution and there is no net movement of water. - **Most cells in organisms are in isotonic solutions, such as blood.** ## Cells in a Hypotonic Solution - **If a cell is in a solution that has a lower Concentration of solute**, the cell is said to be in a **hypotonic solution.** - **There is more water outside of the cell than inside.** - **As a result of osmosis, the net movement of water through the plasma membrane is into the cell.** - **Pressure generated as water flows through the plasma membrane is called osmotic pressure.** - **In an animal cell, as water moves into the cell, the pressure increases, and the plasma membrane swells.** - **If the solution is extremely hypotonic**, plant cells do not burst because they have a rigid cell wall that supports them. - **As the pressure inside a cell increases, the plant's central vacuole fills with water,** pushing the plasma membrane against the cell wall. ## Cells in a Hypertonic Solution - **When a cell is placed in a hypertonic solution, the concentration of the solute outside of the cell is higher than it is inside.** - **During osmosis, the net movement of water is out of the cell.** - **Animal cells in a hypertonic solution shrivel because of decreased pressure in the cells.** - **Plant cells in a hypertonic solution lose water, mainly from the central vacuole.** - **The plasma membrane shrinks away from the cell wall. Loss of water in a plant cell causes wilting.** ## Active Transport - **Sometimes substances must move from a region of lower Concentration to a region of higher concentration.** This movement of Substances across the plasma membrane against a concentration gradient requires energy, therefore it is called **active transport.** - **Carrier proteins** are commonly called pumps. ## Na+/K+ ATPase Pump - **This is an Active transport pump found in the plasma membrane of animal cells.** ## Transport of Large Particles - **Some substances are too large to move through the plasma membrane by diffusion or transport proteins** and must get inside the cell by a different process. - **Endocytosis** is the process by which a cell surrounds a substance in the outside environment, enclosing the substance in a portion of the plasma membrane. The membrane then pinches off and leaves the substance inside the cell. - **Exocytosis** is the secretion of materials at the plasma membrane. ## Check Your Progress **Cells maintain homeostasis using passive and active transport.** - List and describe the types of cellular transport. **Concentration, temperature, and pressure affect the rate of diffusion.** - Explain the role of the cell membrane during passive transport and active transport. **Cells must maintain homeostasis in all types of solutions, including isotonic, hypotonic, and hypertonic.** - Sketch a before and an after diagram of an animal cell placed in a hypotonic solution. - Contrast how facilitated diffusion is different from active transport. **Some large molecules are moved into and out of the cell using endocytosis and exocytosis.** - Describe some organisms that normally live in pond water contain water pumps. - Describe a scenario that might reverse the action of the pump. - Summarize the role of the phospholipid bilayer in cellular transport in living cells.