2.5.2- Diffusion Across Membranes Flashcards
Define what facilitated diffusion is.
Movement of molecules from
An area of high to low concentration of that molecule, across a partially permeable membrane via protein channels or carriers.
What does the abbreviation “ATP” stand for?
Adenosine triphosphate
Describe the role of ATP within cells
To provide cellular energy to drive the biochemical processes to sustain life
What are substances that can pass across cellular membranes without using any of the cells metabolic energy and only use the kinetic energy of the molecules called?
Passive processes.
All molecules have ________ _________ and can move freely and randomly when in gas and liquid media.
Kinetic energy
Explain what will naturally happen to molecules in gas or liquid media when there is a high concentration of the certain molecule in an area.
They will dump into each other as they randomly move about and will spread further from each other and will move so they’re in lower concentration, until they’re evenly dispersed.
When molecules are evenly dispersed but are still moving randomly, there is no net diffusion and they have reached _______
Equilibrium
Define what diffusion is.
Momentum of molecules from an area of high concentration of that molecule to low- possible across a membrane.
Explain how come molecules, that are small, e.g. Oxygen and CO2 can pass through the cellular membrane
Via simple diffusion
How can day soluble molecules like steroid hormones, pass through the membrane- even if they’re larger?
They an diffuse through the membrane as they dissolve in the lipid bilayer- they’re still moving down the concentration gradient.
Explain why it is a ‘special case’ how water can pass through the bilayer by unfacilitated diffusion.
Water is polar and insoluble in the phospholipid bilayer so it would be thought the membrane was impenetrable by water
Why can water in fact move move through the membrane via direct diffusion?
It is present in such high quantities, it allows direct diffusion
Explain how membranes where very high water movement rates are required are adapted to change to this.
Aquaporins- specific water channel proteins- are present to cross through the membrane without the challenge of passing through the lipid environment
Explain how the concentration gradient is maintained in cells, despite diffusion into the cells- in general terms.
Many of the molecules that enter cells then go into organelles- hence, the concentration gradient is maintained and more molecules can enter the cell
Explain how the oxygen concentration is Maintained within cells.
Oxygen diffuses to cytoplasm and then to mitochondria for aerobic respiration
Explain how the CO2 concentration is maintained within palisade mesophyll cells of a plant leaf.
CO2 diffuses into cytoplasm then to chloroplasts for use in photosynthesis.
Factors what alter the kinetic energy of molecules will them effect…
The rate of diffusion
List the five factors that will alter the kinetic energy of molecules, hence, altering the rate of diffusion
~Temperature ~diffusion distance ~surface area ~size of diffusing molecule ~concentration gradient
Describe the type of molecules that will pass through the lipid bilayer via protein channels
Small and polar molecules
Explain why polar molecules are insoluble in lipids.
They have an electrical charge, hence, are unable to interact with the hydrophobic rails of the lipid bilayer.
What is the average diameter of a protein channel?
0.8nm
Cholesterol in membranes reduces the permeability of the membrane to…
Small and water soluble molecules
Why can a glucose molecule not diffuse through a protein channel in a membrane?
They are too large
Describe the type of molecule that a transmembrane protein carrier carries.
Molecules that are too large to pass through a protein channel
