Diffusion is the net movement of atoms or molecules from an area of high concentration to an area of low concentration
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What sort of process is diffusion?
Passive, meaning no energy is required.
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Describe diffusion in solids, liquids and gases
Solids: little diffusion because no movement, liquids & gases: much more diffusion because particles are free to move anywhere
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What does Facilitated Diffusion do?
It assists larger molecules, polar molecules and ions to pass through the membrane.
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How does this occur?
Uses proteins in the membrane - either carrier or channel. Ions & small polar molecules use channel proteins. Larger molecules use carrier proteins that are specific to the substance.
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How do the carrier proteins work?
The molecule attaches to the protein which then changes shape. This transfers the molecule to the other side.
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Does Active Transport require energy?
Yes, because particles cannot pass passively up a concentration gradient.
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How is it carried out?
Uses carrier proteins. ATP provides the energy. Each carrier is specific. Some do two-way active transport, pumping one substance into the cell and another out at the same time.
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Define Osmosis
Osmosis is the net movement of water molecules from a dilute solution to a concentrated solution across a partially permeable membrane.
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How is osmosis different from diffusion & active transport?
It's water molecules only. It's through a partially permeable membrane.
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How do you refer to the concentration of water?
Water potential
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If the water potential is higher than an animal cell, what happens?
Too much water diffuses into the cell and it BURSTS
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If the water potential is equal to an animal cell, what happens?
Nothing
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If the water potential is lower than an animal cell, what happens?
Too much water diffuses out of the cell and it becomes CRENATED
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If the water potential is higher than a plant cell, what happens?
Too much water diffuses into the cell and it is TURGID
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If the water potential is equal to a plant cell, what happens?
Nothing
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If the water potential is lower than a plant cell, what happens?
Too much water diffuses out of the cell and it becomes PLASMOLYSED
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What is endocytosis?
The process by which cells absorb molecules by engulfing them.
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What two forms of endocytosis are there?
Phagocytosis and Pinocytosis
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Describe Phagocytosis
Protrusions called pseudopodia extend from the cell and wrap themselves around a larger particle. The membrane fuses to seal the particle into a vesicle.
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Describe Pinocytosis
The plasma membrane invaginates inwards, allowing the molecules in, then the membrane fuses around the molecules to form a vesicle.
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What is exocytosis?
The process where substances are secreted and from a cell.
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How does it occur?
It is a reversal of pinocytosis, so the vesicle containing the particles reaches the membrane which then parts, allowing the substance out.
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