Transport Across Cell Membranes- Diffusion and Osmosis Flashcards

1
Q

Suggest how cell membranes are adapted for other functions

Glycoproteins/lipids and phospholipid

A
  • Phospholipid bilayer is fluid–>Membrane can bend for vesicle formation/Phagocytosis
  • Glycoproteins/glycolipids act as receptors/antigens–> involved in cell signalling/ recognition
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2
Q

Describe how movement across membranes occcurs by simple diffusion (4)

A
  • Lipid soluble(non polar) or very small substances e.g. O2, steroid hormones
  • Move from an area of higher conc to an area of lower conc, down a conc gradient
  • Across phospholipid bilayer
  • Passive- doesnt require energy from ATP / respiration (only kinetic energy of substances
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3
Q

Describe how movement across membranes occur by facilitated diffusion (4)

A

● Water-soluble / polar / charged (or slightly larger) substances eg. glucose, amino acids
● Move down a concentration gradient
● Through specific channel / carrier proteins
● Passive - doesn’t require energy from ATP / respiration (only kinetic energy of substances)

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4
Q

Explain the role of carrier and channel proteins in facilitated diffusion (3)

A
  • Shape/charge of protein determines which substances move
  • Channel proteins facilitate diffusion of water-soluble substances
    -Hydrophilic pore filled with water
    -May be gated (can open and close)
  • Carrier proteins facilitate diffusion of slightly larger substances
    -Complementary substance attaches to binding site
    -Protein changes shape to transport substance
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5
Q

Describe how movement across membranes occurs by osmosis (4)

A
  • Water moves /diffuses
  • From an area of high to low water potential/down a water potential gradient
  • Through a partially permeable membrane
  • Passive- doesnt require energy from ATP/respiration (only kinetic energy of substances)
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6
Q

How do the molecules move in simple diffusion

A

The molecules need to have kinetic energy

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7
Q

How do molecules diffuse across a membrane in simpel diffusion

A

They must be lipid soluble(polar) and small

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8
Q

How does facilitated diffusion work

A

Protein channels form tubes filled with water and this enables water-soluble ions to pass through teh mmebrane
This is still selective as the channel proteins only opne in the presence of certain ions when the bind to the protein
Carrier proteins will bond with a molcule such as glucose which causes a change in the shape of the protein. This shape change enables the molecule to be released to the other side of the membrane

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9
Q

What is water potential

A

The pressure created by water molecules and it is measured in kPa represented with the trident symbol
The more negative the water potential is the more solute must be dissolved in it

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10
Q

Define isotonic hypotonic and hypertonic

A

Iso- Same water potential in solution and within the cell
Hypo-When the water potential of a solution is more positive(closer to 0) than the cell
Hyper- When the water potential of a solution is more negative than the cell

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11
Q

What happens if an animal cell and a plant cell were in a hypotonic solution

A

Water will enter the cell by osmosis causing the animal cell to burst but for a plant cell it will become turgid

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12
Q

What happens if an animal cell and a plantcell were placed in a hypertonic solution

A

Water will leave the cell by osmosis causing them to shrivel

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13
Q

WHAT CAN PASS THROUGH BY FACILITATED DIFFUSION?

A

Larger molecules like glucose or amino acids.
Charged/polar/hydrophilic molecules
Water soluble molecules
Molecules that can’t readily pass through the cell membrane via simple diffusion.

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14
Q

WHAT CAN GO THROUGH MEMBRANE BY SIMPLE DIFFUSION AND WHY?

A

Gases - Oxygen and carbon dioxide diffuse into and out of the cell for respiration.
Hydrophobic molecules - don’t repel from the hydrophobic fatty acid tails
Non-polar/uncharged - don’t repel from the hydrophobic fatty acid tails
Water - small molecule
Lipid-soluble (capable of dissolving in lipids) - dissolve in phospholipid bilayer to move through it
Small molecules - fit between phospholipids

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15
Q

FACTORS AFFECTING RATE OF FACILITATED DIFFUSION

A

Concentration gradient
Greater = faster
Up to a point if all proteins are in use. As equilibrium reaches, rate plateaus.

Number of protein channels/carriers
More = faster
Once all in use, the rate of diffusion cannot increase even if other factors increase.

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16
Q

FACTORS AFFECTING RATE OF OSMOSIS

A

Water potential gradient
Higher gradient = faster
As osmosis takes place, the difference in water potential on either side of the membrane decreases, so the rate of osmosis levels off over time.

Thickness of exchange surface
Thinner = faster
Shorter distance for the water molecules to travel

Surface area of exchange surface
Larger = faster
More area for the water molecules to travel through in a set amount of time.