Cell Membranes and Transport Flashcards
describe the fluid mosaic model of the plasma membrane and describe how it allows the cell membrane to be selectively permeable
the fluid mosaic model is used by biologists to describe a membrane’s structure - diverse protein molecules suspended in a fluid phospholipid bilayer. it illustrates the structure and function of a plasma membrane which, like all cellular membranes, is selectively permeable, which means it allows some substances to cross more easily than others
explain how the chemical properties of the molecules that compose the membrane (such as phospholipids and proteins) relate to the structure and function of the membrane
heads are hydrophilic and tails are hydrophobic, so they form phospholipid bilayer
phospholipids bilayer makes it difficult for large or charged particles to go through so you need different types of transport
understand the process of diffusion and explain why it occurs, and example
diffusion is when molecules move to equalize concentration; spread out. diffusion is random and spontaneous, molecules move down a concentration gradient, molecules have kinetic energy which makes them move about randomly, as a result, molecules reach equilibrium. it is a process of PASSIVE transport, so no energy is required, and is due to natural kinetic energy. molecules move high to low concentration. the rate of diffusion is determined by the steepness of the concentration gradient, temperature, surface area, and the type of molecule or ion diffusing EX: CO2, O2
explain the phenomenon of osmosis and its importance to cell function for both plants and animals
osmosis is a type of passive transport, and a special form of diffusion using water, water flows from a high to low concentration across a membrane in an attempt to reach equilibrium. in plants, osmosis is responsible for the absorption of water through their roots, which hydrates the plant and distributes water throughout the body. in animals, osmosis absorbs and distributes water throughout the bloodstream, to hydrate the entire body
differentiate between passive and active transport
passive transport contains diffusion, osmosis and facilitated diffusion, requires NO energy, molecules move from a high to low concentration, in spontaneous movement down a concentration gradient across a membrane. active transport contains sodium/potassium pump and a proton pump, requires energy, molecules move from a low to high concentration against the concentration gradient
describe how an action potential is started and how it relates to active transport (sodium-potassium pumps)
action potential is a massive change in membrane voltage that transmits a nerve signal along an axon. it begins at resting potential when the membrane is polarized (inside more negatively charged), then the stimulus is applied and if strong enough the voltage rises to the threshold, and once reached it triggers the action potential. the membrane depolarizes and the interior becomes more positive. the sodium-potassium pumps maintain the concentration gradients of the ions, using energy to move sodium out of the neuron and potassium in. as more positively charged potassium ions diffuse out of the cell, the inside becomes more negative and the electrical potential difference across the membrane is resting potential
describe how active transport is used in plants, bacteria, and fungus (proton pumps)
proton pump is the major electrogenic pump in plants, fungi, and bacteria. it pumps hydrogen out of cells and sets up the electrochemical gradient, stores energy and is used to do co-transport. since it sets up co-transport it this mechanism transports sucrose in plants uphill into specialized veins of leaves to be transported to nonphotosynthetic parts of the plant. It can be used in similar ways in bacteria in fungus
describe the structures and regulatory mechanisms that organisms have to manage living in aquatic environments
osmoconformers are organisms whose internal environment is isotonic with the external environment, so they do not adjust internal osmolarity (ex: jellyfish). osmoregulators are organisms whose body fluids are NOT isotonic with the external environment, so they must adjust internal osmolarity (ex: fish and paramecium)
predict, based on a material’s size and chemical characteristics (polarity), by what mechanism it will traverse the membrane
if a molecule is small and uncharged it will traverse by diffusion or osmosis (if it’s water). if it is a lipid-soluble molecule like a hydrocarbon, it will traverse by diffusion. if it is a water-soluble molecule like glucose then it will use facilitated diffusion. if it is an ion it will use facilitated diffusion, because it has a charge.
types of passive transport
diffusion, osmosis, and facilitated diffusion
characteristics of passive transport
- requires no energy
- moves from high to low concentration
- spontaneous movement down a concentration gradient across a membrane
what is the purpose of diffusion, example molecules?
to reach equilibrium, CO2, O2
types of osmosis solutions
hypotonic, hypertonic, isotonic
what happens to a cell placed in a hypotonic solution
animal cell - swell and burst (cytolysis)
plant cell - max turgor pressure - turgid (healthy)
what happens to a cell placed in a hypertonic solution
animal cell - shrivel and die (crenation)
plant cell - central vacuole shrinks, membrane caves in (death) no turgor pressure (plasmolysis)
what happens to a cell placed in an isotonic solution
animal cell - healthy
plant cell - flaccid (wilty) but okay (not max turgor pressure)
what molecules diffuse across membranes and why
oxygen b/c it’s nonpolar and small, diffuses very quickly
carbon dioxide b/c it’s nonpolar and small, diffuses quickly
water b/c it’s polar but very small, and diffuses quickly
what direction do the molecules go when they diffuse across a membrane
oxygen goes in, carbon dioxide goes out, water goes back and forth (both ways)
what determines the rate of diffusion
the steepness of the concentration gradient, temperature, surface area, and the type of molecule or ion diffusing
how does the steepness of the concentration gradient affect the rate of diffusion
the bigger the difference between the two sides of the membrane, the quicker the rate of diffusion
how does temperature affect the rate of diffusion
higher temperature gives molecules or ions more kinetic energy, which makes molecules move faster, so diffusion is faster
