2.3-Transport across cell membranes Flashcards

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1
Q

Explain the functions of the cell-surface membrane.

A
  • Isolates cytoplasm from extracellular environment.
  • Selectively permeable to regulate transport of substances.
  • Involved in cell signalling/cell recognition .
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2
Q

Describe the fluid mosaic model of membranes.

A

Fluid: phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape.
Mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded.

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3
Q

Explain the role of cholesterol and glycolipids in membranes.

A

Cholesterol: steroid molecule in some plasma membranes; connects phospholipids and reduces fluidity to make bilayer more stable.
Glycolipids: cell signalling and cell recognition.

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4
Q

Explain the functions of extrinsic and intrinsic proteins in membranes.`

A

Extrinsic:
- Binding sites/ receptors e.g. hormones
- Antigens (glycoproteins)
- Bind cells together
- Involved in cell signalling
Intrinsic:
- Electron carriers (respiration/photosynthesis)
- Channel proteins (facilitated diffusion)
- Carrier proteins (facilitated diffusion/ active transport)

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5
Q

Explain the functions of membranes within cells.

A
  • Provide internal transport system.
  • Selectively permeable to regulate passage of molecules into/out of organelles.
  • Provide reaction surface.
  • Isolate organelles from cytoplasm for specific metabolic reactions.
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6
Q

Name and explain 3 factors that affect membrane permeability.

A
  • Temperature: high temperature denatures membrane proteins/phospholipid molecules have more kinetic energy and move further apart.
  • pH: changes tertiary structure of membrane proteins.
  • Use of solvent: may dissolve membrane.
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7
Q

Outline how colorimetry could be used to investigate membrane permeability.

A
  1. Use plant tissue with soluble pigment in vacuole. Tonoplast and cell-surface membrane disrupt = higher permeability = pigment diffuses into solution.
  2. Select colorimeter filter with complementary colour.
  3. Use distilled water to set colorimeter to 0. Measure absorbance/ % transmission value of solution.
  4. High absorbance/ low transmission = more pigment in solution.
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8
Q

Define Osmosis

A

The net movement of water molecules for a regios of higher water potential to a region of lower water potential through a partially permeable membrane.

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9
Q

What is water potential?

A
  • Pressure created by water molecules measured in kPa.
  • Water potential of pure water at 25C & 100 kPa: 0
  • More solute = water potential more negative.
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10
Q

How does osmosis affect plant and animal cells?

A
  1. Osmosis INTO cell:
    - Plant: protoplast swells = cell turgid
    - animal = lysis
  2. Osmosis OUT of cell:
    - Plant: protoplast shrinks = cell flaccid
    - Animal: Crenation
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11
Q

Suggest how a student could produce a desired concentration of solution from a stock solution.

A
  • Volume of stock solution = required concentration x final volume / concentration of stock solution.
  • Volume of distilled water = final volume needed - volume of stock solution.
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12
Q

Define simple diffusion.

A

The passive movement of small, non-polar, lipid soluble molecules from an area of high concentration to an area of low concentration along a concentration gradient.

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13
Q

Define facilitated diffusion.

A

It requires a channel protein in the cell membrane to transport polar molecules, charged and water soluble molecules across the mebrane.

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14
Q

Explain how channel and carrier proteins work.

A
  • Channel: hydrophilic channels bind to specific ions = one side of the protein closes & the other opens.
  • Carrier: binds to complementary molecule = conformational change releases molecule on the other side of membrance; in faciliated diffusion, passiv process; in active transport, requires energy from ATP hydrolysis.
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15
Q

Name 5 factors that affect the rate of diffusion.

A
  • Temperature
  • Diffusion distance
  • Surface area
  • Size of molecule
  • Difference in concentration (how steep the concentration gradient is)
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16
Q

State Fick’s Law

A

(Surface area x difference in concentration)/ diffusion distance

17
Q

How are cells adapted to maximise the rate of transport across their membranes?

A
  • Many carrier/ channel proteins
  • Folded membrane increases surface area
18
Q

Explain the difference between the shape of a graph of concentration (x-axis) against rate (y-axis) for simple vs faciliated diffusion.

A

Simple Diffusion: straight diagonal line; rate of diffusion increases proportionally as concentration increases.
Faciliated Diffusion: straight diagnonal line later levels off when all channel/ carrier proteins are saturated.

19
Q

Define active transport.

A
  • Active process: ATP hydrolysis releases phosphate group that binds to carrier protein, causing it to change shape.
  • Specific carrier protein transports molecules/ ions from an area of low concentration to an area of higher concentration against a concentration gradient.
20
Q

Compare and contrast active transport and facilliated diffusion.

A
  • Both may involve carrier proteins.
  • Active transport requires energy from ATP hydrolysis; faciliated diffusion is a passive process.
  • Faciliated diffusion may also involve channeol proteins.
21
Q

Define co-transport.

A
  • Movement of a substance against its concentration gradient is coupled with the movement of another substance down its concentration/ electrochemical gradient.
  • Substances bind to complementary intrinsic protein:
    Symport: transports substances in the same direction.
    Antiport: transports substance in opposite direction e.g. sodium-potassium pump.
22
Q

Explain how co-transport is involved in the absorption of glucose/ amino acids in the small intestine.

A
  1. Na+ actively transported out of epithelial cells & into bloodstream.
  2. Na+ concentration lower in epithelial cells than lumen of gut.
  3. Transport of glucose/ amino acids from lumen to epithelial cells is ‘coupled’ to faciliated diffusion of Na+ down electrochemical gradient.