Transports across membrane Flashcards

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1
Q

What is diffusion?

A
  • Net movement of molecules from a region of high concentration to low.
  • Molecules reach an concentration equilibrium, where they are evenly spread out. No net movement.
  • passive process, have natural kinetic energy
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2
Q

What substances can be transported via diffusion?

A
  • Oxygen, non polar and small so diffuses quickly
  • Carbon dioxide, polar but small so diffuses quickly
  • Water, polar but small so diffuses quickly
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3
Q

What factors affect the rate of diffusion?

A
  • temperature
  • steep concentration gradient
  • thickness of the membrane
  • large surface area to volume ratio (SA:V)
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4
Q

How does temperature affect the rate of diffusion?

A
  • Increase the amount of thermal energy, then particles have more energy to transfer into kinetic energy
  • Use kinetic energy to move faster and more randomly
  • Faster they move, quicker they will move down the concentration gradient
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5
Q

How does a steep concentration gradient affect the rate of diffusion?

A
  • Greater the difference between concentration in the two regions, the faster particles will move ‘down’ the concentration gradient to the area of lower concentration
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6
Q

How does the thickness of the membrane affect the rate of diffusion?

A
  • Exchange surfaces are thin and usually one cell thick
  • plasma membrane is thin - approximately 7.5nm in width
  • Surfaces also tend to be moist which allows gases to dissolve in the fluid first making diffusion easier
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7
Q

How does large SA:V ratio affect the rate of diffusion?

A
  • All exchange surfaces consist of many, microscopic structures which collectively achieve a much larger surface area than 1 large structure
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8
Q

What substances does the phospholipid bilayer form a barrier to?

A
  • large molecules
  • water soluble substances
  • charged molecules
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9
Q

What is facilitated diffusion?

A
  • When the molecules pass through protein carriers or channels instead of passing between the phospholipids
  • moves from high to low concentration
  • more protein channels, mean higher rates of diffusion
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10
Q

What substances can be transported via facilitated diffusion?

A
  • large polar molecules like glucose and amino acids

- charged molecules like Na+ or Cl-

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11
Q

How is the placenta adapted for diffusion?

A
  • large SA:V ratio
  • thin shape to increase surface area and decrease diffusion distance
  • located towards centre of the body to maintain warm temperature
  • blood is always flowing through the placenta to maintain gradient of high oxygen to low oxygen
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12
Q

What is active transport?

A
  • movement of molecules from a low to high concentration
  • Energy (ATP) is required to move substances against concentration gradient
  • Use protein carriers in the membrane
  • act as a pump
  • selective process: specific substances transported by specific carrier proteins
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13
Q

What is the general process of active transport?

A
  1. molecule or ion to be transported binds to receptors in channel of carrier protein on outside of the cell
  2. on inside of the cell ATP binds to carrier protein and is hydrolysed into ADP and phosphate
  3. the protein changes shape, opening up to the inside of the cell
  4. molecule or ion released into inside of the cell
  5. phosphate molecule released from carrier protein and recombines with ADP to form ATP
  6. carrier protein returns to original shape
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14
Q

What can be transported by active transport?

A
  • glucose, could be in short supply

- amino acids

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15
Q

What is bulk transport?

A
  • another form of active transport
  • large molecules like enzymes, hormones and whole cells like bacteria are too large to move through channel or carrier proteins
  • moved into and out of cell by bulk transport
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16
Q

What is endocytosis?

A
  • bulk transport of material into cells
  • phagocytosis (transport solids into cells) and pinocytosis (transports of liquids into cells)
  • membrane enfolds the material forming a vesicle to enter the cell
17
Q

What is exocytosis?

A
  • movement out of cells
  • opposite of endocytosis
  • vesicles formed by Golgi body move towards and fuse with the cell surface membrane and release content outside of cell
18
Q

What is co-transport?

A
  • Facilitated diffusion where a molecule will move through a membrane with the assistance of another molecule
  • E.g. glucose and sodium, moving from the blood into the small intestine epithelial cells
19
Q

What is osmosis?

A
  • diffusion of water from high concentration of water molecules (high water potential) to a low concentration of water molecules (low water potential) across a partially permeable membrane
  • until reached equilibrium