Biology Revision- Transport across membranes

What is the role of the cell membrane?
It controls the movement of molecules in and out of the cell
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What is the cell membrane made up of?
-phospholipids -proteins/glycoproteins - Glycolipids - Cholesterol
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What is cholesterol?
A type of lipid with the molecular formula C27 H46 O.
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What is the role of cholesterol?
It is important in controlling membrane fluidity. The more cholesterol the less permeable the membrane. Cholesterol is also important in keeping membranes stable at normal body temperature-without it cells would burst open
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Hydrophobic substances. e.g. fats. move high-low concentration. passive. no energy
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Facilitated diffusion?
Large molecules or charged. e.g glucose. High-low concentration. passive. Carrier protein involved. No energy
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Active Transport?
Toxic molecules. E.g. urea. Move from a low-high concentration. Active. Carrier protein and ATP involved. Energy required.
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What is osmosis?
Osmosis is the diffusion of water. It is the net movement of water molecules from a region of high water concentration to a region of low water concentration, through a partially permeable membrane
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What is water potential?
Water potential is the tendency of water molecules in a system to move
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What is an isotonic solution?
It refers to 2 solutions having the same osmotic pressure across a semi permeable membrane. This state allows for free movement of water across the membrane without changing the concentration on solutes on either side
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What does hypertonic mean?
Having a higher osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid.
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What does hypotonic mean?
Having a lower osmotic pressure than a particular fluid, typically a body fluid or intracellular fluid
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What are the functions of the proteins in the membrane?
Provide structural support/ Act as carriers transporting water soluble substances across the membrane/ Allow active transport across the membrane by forming ion channels/ Form recognition sites by identifying cells/ Help cells adhere together
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What is 1 more function of a protein in the membrane?
Act as receptors e.g. for hormones
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What is a solute?
Any substance that is dissolved in water
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What is the water potential of pure water?
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What processes is active transport used in?
-The uptake of glucose and amino acids in the small intestine. - Absorption of mineral ions by plant roots
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What are the 4 features of an efficient gas exchange surface?
Large surface area/ Short diffusion pathway/ Steep diffusion gradient/ Good supply of blood
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How are intestinal epithelial cells adapted?
Microvilli-increase surface area for absorption. Lots of mitochondri. Lots of NA/K pumps/ Lots of Na/ Glucose carrier proteins to uptake glucose/ Lots of glucose channel proteins for facilitated diffusion of glucose
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Oxygen and water move through plasma membranes into cells. Describe 2 ways in which these movements are similar?
They both do not require energy/ Both movements are down a concentration gradient
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By what process does urea pass from the blood into the dialysis fluid?
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Suggest 2 reasons for keeping the fluid in the dialysis machine at 40 degrees rather than room temperature?
Higher rate of diffusion/ Prevents cooling of the blood
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The blood and the dialysis fluid flow in opposite directions in the dialysis machine. Explain the advantage of this?
The blood always meets fluid with lower concentration of urea so diffusion can take place along the whole length of surface
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Give 1 function of a glycolipid?
Acts as a recognition site e.g. for cholera toxins
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Give 1 similarity in the way in which active transport and facilitated diffusion transport substances across the membrane?
A carrier protein is involved in both active transport and facilitated diffusion
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Give 1 way in which active transport differs from facilitated diffusion?
Active transport requires external energy in the form of ATP whereas facilitated diffusion does not
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Card 2


What is the cell membrane made up of?


-phospholipids -proteins/glycoproteins - Glycolipids - Cholesterol

Card 3


What is cholesterol?


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Card 4


What is the role of cholesterol?


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