9.2 Study Guide Flashcards
Describe simple diffusion, specifically how molecules move from _____ to _____. What causes molecules to move in this way?
Simple diffusion is the natural movement of molecules from an area of high concentration through a barrier to an area of low concentration. Molecules tend to move in such a way because of the natural randomness of their movements and trajectories causing them to be almost infinitely more likely to disperse into ‘empty’ space. In cells, simple diffusion generally can only be done by small, nonpolar molecules through the cell membrane.
Explain how facilitated diffusion differs from simple diffusion. Why would cells need to perform facilitated diffusion to function?
Facilitated diffusion is an alternate form of diffusion that allows larger and/or polar molecules to perform diffusion within cells. Instead of passing directly through the cell membrane, these molecules pass through specially-made protein ‘channels’ that create wide, non-repulsory tunnels in and out of cells, each for specific molecules. Facilitated diffusion allows cells to take in and get rid of all the molecules they need to function.
Define osmosis and explain the three types of concentration disparity between two separated solutions.
Osmosis is the natural movement of a solvent between similar solutions across a semi-permeable membrane due to its natural concentration to one of the solutions’ greater concentration of solute. It makes the two solutions’ ratios of solute to solvent equally proportional. Any of two similar separated solutions will be either hypertonic, hypotonic, or isotonic, A hypertonic solution has a higher ratio of solute to solvent compared to the other, a hypotonic solution has a lower ratio, and two isotonic solutions have equal ratios.
Explain how active transport is different from simple diffusion, facilitated diffusion, and osmosis. Why would cells perform this function when they have the other three?
While simple diffusion and facilitated diffusion move molecules from high to low concentration, and while they and osmosis are passive and require no energy, active transport is the cell-driven movement of molecules in and out of a cell against the natural concentration gradient (that is to say, moves from low to high) and requires energy in the form of ATP. Cells perform active transport to take in and get rid of the molecules that don’t naturally move in and out of the cell through diffusion and osmosis.
Describe the two forms of active transport and how they are different.
The two forms of active transport are endocytosis and exocytosis. Endocytosis is the movement of molecules into a cell through active transport, while exocytosis is the movement of molecules out of the cell through active transport.
What about the properties and structures of phospholipids makes them ideal for making up the main structure of cell membranes?
The phospholipids that make up cell membranes are made up of two major sections - the hydrophilic head, which includes phosphorous and is polar, and the hydrophobic tail, which is made of carbon and hydrogen and is nonpolar. These different parts cause the molecules to naturally organize themselves into a bilayer in which the hydrophilic heads point outward towards water and the hydrophobic tails point inward at each other away from water. This bilayer is perfect as a semi-permeable membrane to surround every cell.
Beyond phospholipids, name at least two types of molecules that make up cell membranes and their functions.
- Cholesterol: Is interspersed around the membrane and binds together patches of the bilayer to produce the perfect amount of rigidity and flexibility for the membrane.
- Carbohydrates: Extend outside of the membrane; act as an identification of the cell as belonging in its body as well as identifiers of other cells.
- Proteins: Some act as channels and pumps to transport molecules through the membrane, while others provide structural support in various ways including anchoring carbohydrates to the membrane.
Explain why a cell with a high ratio of surface area to volume is the most ideal based on what you know about diffusion.
A cell with high surface area has much more membrane to take in and get rid of molecules through, while a cell with high volume requires molecules to move over longer distances to get around the cell and pass in and out. Thus, a cell with high surface area and low volume can collect vital molecules and excrete unwanted molecules the fastest.
A cell whose cytosol is 90% water and 10% solutes is submerged in a substance that is 88% water and 12% solute. In which direction will water move to equalize the concentrations?
Because the solution outside the cell has a higher ratio of solute to solvent than the solution inside the cell, water from inside the cell will move out of it to equalize the concentration ratios.
Two substances made entirely of water and solutes are separated by a barrier that is impermeable to water, but not to the solutes. Solution A consists of 49.3% water, while solution B consists of 53.2% solutes. In which direction will the solutes move across the barrier to equalize the concentrations?
As solution A consists of 49.3% water, it also consists of 50.7% solute. This means solution A has a lower ratio of solute to solvent and, thus, that solute from solution B will move to solution A to equalize the ratios.
