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What do permeable and impermeable mean in relation to membranes?
The ability of substances to move through the membrane. Permeable means they can move freely, impermeable means that movement is restricted through the membrane.
What does the term selectively permeable mean?
It refers to the ability of the membrane to let specific substances through, while blocking others.
What types of substances is the plasma membrane permeable to?
Small, non-charged molecules, such as oxygen and carbon dioxide.
What types of substances is the plasma membrane impermeable to?
The plasma membrane is impermeable to ions and large uncharged particles.
What type of substances is the plasma membrane slightly permeable to?
Small polar molecules such as water.
What is a concentration gradient?
Refers to the difference in the concentration of a solute on either side of a membrane.
What is an electrical gradient?
The difference in charge on either side of a membrane.
What is the difference between passive and active processes to move a substance across a membrane?
Passive process rely on diffusion principles and electrostatic attraction to move substances across a membrane, while passive process will utilise another form of energy, often ATP, to do so. Active processes include ion channels and carrier proteins.
What is diffusion? Explain why this occurs.
Diffusion is the movement of solute molecules to areas of less concentration. It occurs because of the random movement all atoms display, which over time sees them take up all space available to them.
What factors influence the rate of diffusion?
- SA-V of solute
- distance over which diffusion must take place
- Mass of diffusing substances
What is the difference between simple and facilitated diffusion?
In simple diffusion substances will diffuse down a concentration gradient, whereas in facilitated diffusion an integrated protein aids in the diffusion.
What is a vesicle?
A small spherical packet made from a phospholipid bilayer. They can merge in and out of the plasma membrane and are used to transport substances throughout the cell.
What is endocytosis?
The movement of particles into a cell by landing on the surface, where they are engulfed in phospholipid membrane which is absorbed moves into the interior.
What is exocytosis?
The moving of particles from a vesicle to the exterior of a cell. The vesicle merges with the plasma membrane, pushing the particles out as it becomes the new exterior surface.
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