Transport across Cell Membranes

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  • Created by: Emily.T
  • Created on: 30-11-17 11:55
What is diffusion?
The net movement of particles (molecules or ions) from an area of high concentration to an area of low concentration
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Is diffusion unidirectional or bidirectional?
Bidirectional, but the net movement will always be to an area of low concentration. This continues until particles are evenly distributed
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Is diffusion an active or passive process?
Passive - no enery is needed for it to happen
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What type of molecules can diffuse straight through the phospholipid bilayer?
Small non-polar molecules, such as Oxygen and Carbon Dioxide, diffuse through the spaces between phospholipids.
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Can water diffuse through the phospholipid bilayer?
Yes, because it is small enough to fit between the phospholipids even though it is polar.
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What is the diffusion of water molecules called?
Osmosis
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What are the four factors that affect the rate of diffusion?
1) Concentration gradient 2) Thickness of exchange surface 3) Surface area 4) Temperature
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How does the concentration gradient affect the rate of diffusion?
The higher the concentration, the faster the rate of diffusion
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How does the thickness of the exchange surface affect the rate of diffusion?
The thinner the exchange surface (means that there's a shorter distance the particles have to travel) the faster the rate of diffusion
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How does the surface area affect the rate of diffusion?
The larger the surface area, the faster the rate of diffusion
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How does temperature affect the rate of diffusion?
The warmer it is, the faster the rate of diffusion because the particles have more kinetic energy so they move faster
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What is facilitated diffusion?
Diffusion across a cell membrane via carrier and channel proteins down a concentration gradient (from an area of high to low concentration
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Is facilitated diffusion active or passive?
Passive - does not use energy
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What type of molecules use facilitated diffusion?
Larger molecules (e.g. amino acids, glucose), ions and polar molecules
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Facilitated diffusion across Carrier proteins:
1) A large molecule attaches to a carrier protein in the membrane 2) The protein changes shape so the binding site moves from one side of the membrane to the other side 3) This release the molecule on the opposite side of the membrane
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Facilitated diffusion across Channel proteins:
Channel proteins are pores in the membrane for charged particles to diffuse through - different channel proteins facilitate the diffusion of different charged particles
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What is active transport?
The movement of molecules across the cell membrane, from a region of low concentration to a region of higher concentration, against a concentration gradient, so energy is needed and Carrier proteins are involved.
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Is active transport an active or passive process?
Active - energy is needed transfer the particles across the membrane via Carrier proteins
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Process of active transport:
1) A molecule attaches to the Carrier protein at its specific binding site 2) Protein changes shape 3) Molecule is released on the other side of the membrane against a concentration gradient
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What is endocytosis?
A process in which cells take in substances from the outside by engulfing and fusing them with its plasma membrane.
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The process of endocytosis:
1) A cell surrounds a substance with a section of its plasma membrane 2) The membrane pinches off to form a vescile inside the cell containing the ingested substance 3) Is an active process so requires ATP for energy
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What is exocytosis?
A process where substances produced by the cell need to be released from the cell
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The process of exocytosis:
1) Vesicles containing the substances pinch off from the sacs of the Golgi apparatus and move towards the plasma membrane 2) Vesicle fuses with the membrane and release their contents outside the cell 3) Is an active process so requires ATP
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Define Osmosis:
The diffusion of water particles across a partially permeable membrane down a water potential gradient - water move from an area of higher water potential to an area of lower water potential
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What does 'water potential' mean?
The likelihood of water molecules to diffuse into or out of a solution
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What is the water potential of pure water and why?
0, which is the highest water potential, because it has no other solutes in it and the water molecules can move freely
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Why does the water potential decrease (from 0) when solutes are added to it?
Because the solutes are attracted to the water molecules so these water molecules can no longer move freely, so the water potential is lowered
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What does a hypotonic solution mean in animal cells?
A solution with higher water potential than the cell. The net movement of water is into the cell and the cell bursts = cytolysis
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What is cytolysis?
When a cell bursts due to an osmotic imbalance that has caused excess water to move into the cell.
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What does an isotonic solution mean in animal cells?
When the solution has the same water potential as the cell. Water molecules pass into and out of the cell in equal amounts. The cell stays the same.
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What does a hypertonic solution mean in animal cells?
When the solution has a lower water potential than the cell. The net movement of water molecules is out of the cell. The cell shrinks = crenation
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What is crenation?
When the cell shrinks due to the loss of water from a cell when the solution is hypertonic
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What does a hypotonic solution mean in a plant cell?
The net movement of water is into the cell causing the vacuole to swell. The vacuole and cytoplasm push against the cell wall, making the cell turgid (swollen)
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What does turgid mean?
When a plant cell has become swollen due to the high water content in the cell
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What does an isotonic solution mean in a plant cell?
The water molecules move into and out of the cell in equal amounts. The cell stays the same.
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What does a hypertonic solution mean in a plant cell?
The net movement of water is out of the cell. The cell becomes flaccid (limp) as the cyotplasm and cell membrane pull away from the cell wall = plasmolysis
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What is plasmolysis?
The shrinking of a plant cell due to the loss of water from osmosis
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Other cards in this set

Card 2

Front

Is diffusion unidirectional or bidirectional?

Back

Bidirectional, but the net movement will always be to an area of low concentration. This continues until particles are evenly distributed

Card 3

Front

Is diffusion an active or passive process?

Back

Preview of the front of card 3

Card 4

Front

What type of molecules can diffuse straight through the phospholipid bilayer?

Back

Preview of the front of card 4

Card 5

Front

Can water diffuse through the phospholipid bilayer?

Back

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