2.5- Diffusion across membrane Flashcards
What is diffusion?
The movement of molecules from an area of high concentration to an area of low concentration; may or not pass through a partially permeable membrane, and does not require ATP.
What is facilitated diffusion?
The movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane via protein channels or carriers. It does not require ATP.
WHat is a passive process?
Cells need to receive raw materials or reactants for biochemical processes. They respire to make ATP, which provides cellular energy to drive these biochemical reactions. Therefore they need oxygen and glucose. They also need to remove toxic metabolic waste products, such as CO2,and they need to export some of the molecules that they make such as enzymes, hormones , etc., without using any of the cell’s metabolic energy. These are passive processes because they only use the kinetic energy of the molecules and do not use ATP.
What is simple diffusion?
All molecules have kinetic energy and can move freely within gas or liquid. This will happen even if they medium is not mixed by shaking or stirring. If there’s a high concentration of a certain type of molecule in an area then the molecules will eventually bump into each other as they randomly move. More will move to an area where they are lower in concentration until they eventually become evenly dispersed?
When do molecules reach equilibrium in simple diffusion?
When the molecules have moved down their concentration gradient, they are still moving randomly but remaining evenly dispersed (no net diffusion).- reached equilibrium
What can be diffused in simple diffusion?
- Molecules such as O2 and CO2, which are small, can pass through the cell membrane by simple diffusion.
- Fat soluble molecules such as steroid hormones even if they are larger can diffuse through the cell membrane as they dissolve in the lipid bilayer. They still move down the concentration gradient.
Why are water molecules a special case?
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Since they are polar and insoluble in lipid, the phospholipid bilayer would seem to be an impenetrable barrier.
- However, water is present in such great concentrations that significant direct diffusion does happen.
- In membranes where a very high rate of water movement is required, there may be specific water channel proteins (aquaporins).
- Aquaporins allow water molecules to cross the membrane without the challenge of moving through a lipid environment
How is the concentration gradient maintained?
Many molecules entering the cells, then pass into organelles and are used for metabolic reactions; this maintains the concentration gradient and keeps more of the molecule entering the cell.
- Oxygen diffusing into the cytoplasm of respiring cells then diffuses into mitochondria and is used for aerobic respiration.
- Carbon dioxide diffusing into the palisade mesophyll cells of a plant leaf will then diffuse into chloroplasts and be used for photosynthesis
These are examples of how CG is maintained
Which factors affect the rate of simple diffusion?
- Temperature.
- Diffusion distance.
- Surface area.
- Size of diffusing molecule.
- Concentration gradient.
What does simple diffusion rely on?
simple diffusion relies on the molecules own kinetic energy and so factors that alter this will affect the rate of diffusion
How does temperature affect diffusion?
As temp increases molecules have more kinetic energy so rate of diffusion will increase.
-As temp decrease rate of diffusion will slow down
How does diffusion distance affect diffusion?
The thicker the membrane across which molecules have to diffuse the slower the rate of diffusion
How does surface area affect diffusion?
More diffusion can take place across a larger surface area. Cells specialised for absorption have extensions to their cell surface membrane called microvilli. These increase the surface area.
How does size of molecule affect diffusion??
Smaller ions/ molecules diffuse more rapidly than large molecules
How does concentration gradient affect diffusion?
The steeper the gradient (the more molecules they are on one side of the membrane compared to the other), the faster the diffusion to the side where there are fewer molecules down the gradient.
