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Topic 2B - Cell Membrane > Exchange Across Cell Membrane - Diffusion > Flashcards

Exchange Across Cell Membrane - Diffusion Flashcards

1
Q

What is an example of passive transport?

A
  • Facilitated diffusion
  • Simple diffusion
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2
Q

What does ‘passive’ mean?

A

Energy comes from the natural, inbuilt motion of particles (kinetic energy)

rather than the external sources such as ATP

net movement of particles from high to low concentration

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3
Q

Properties of diffusion particles

A
  • All particles are constantly in motion due to the kinetic energy they possess
  • Motion is random - no set pattern in which the particles move around
  • Particles are constantly bouncing off one another as well as objects e.g side of vessel they are contained
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4
Q

What is the definition of diffusion?

A

Net movement of molecules/ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed

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5
Q

What molecules can diffuse straight through the cell membrane?

(simple diffusion)

A

Small and non-polar molecules (makes them soluble in lipids - dissolve in hydrophobic bilayer)

e.g oxygen

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6
Q

Why do charged ions and polar molecules do not diffuse easily?

A

Hydrophobic nature of the fatty acid tails of the phospholipids in the membrane

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7
Q

What factors affect facilitated diffusion?

A
  • Concentration gradient
  • Number of channel or carrier proteins
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8
Q

The concentration gradient is one of these factors – how does the concentration gradient affect the rate of diffusion?

(e.g Ventilation of air in lungs)

A

The steeper the concentration gradient the higher the rate of diffusion.

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9
Q

How does the concentration gradient affect diffusion?

A
  • The higher it is the faster the rate of diffusion
  • As diffusion takes place the difference between two sides decreases until it reaches an equilibrium (both sides are equal)
  • Diffusion slows down over time
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10
Q

How does surface area affect the rate of diffusion?

(Microvilli , Alveoli , cristae , thylakoids,

A

Larger surface area the faster rate of diffusion

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11
Q

How does concentration gradient affect facilitated diffusion?

A

Higher concentration gradient , faster rate

As equilibrium reached , rate of diffusion will level off

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12
Q

How does thickness of the exchange surface affect the rate of diffusion?

A

The thinner the exchange surface (i.e shorter distance the particles have to travel) the faster the rate of diffusion

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13
Q

How does microvilli increase the rate of diffusion?

A

Some cells e.g epithelial cells have microvilli (projections in cell surface membrane folding up on itself)

It gives cell a large surface area - increase rate of diffusion

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14
Q

What is facilitated diffusion?

A

The passive movement of molecules crosses the cell membrane in a specific transmembrane protein

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15
Q

What molecules are used for facilitated diffusion?

A
  • Charged ions
  • Polar molecules
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16
Q

Where does diffusion occur with concentration gradient?

A

Down a concentration gradient

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17
Q

What two proteins are involved in facilitated diffusion?

A
  • Carrier proteins
  • Channel proteins
18
Q

What do channel proteins form?

A

Water-filled hydrophobic channels across the membrane

19
Q

What type of substances do channel proteins pass through?

A

Water-soluble susbtances

small charged or polar molecules e.g ions Na + , K + , Ca2+

20
Q

How are channel proteins selective in the opening of the presence of a specific ion?

A

If the particular ion is not present , channel remains closed - control entry and exit of ions

21
Q

How do carrier proteins transport large molecules across cell membrane?

A

Large molecule bind with the protein causing it to change shape

Releases molecule on the opposite side of the membrane

22
Q

What type of molecules are used with carrier proteins?

A

e.g glucose specific to carrier protein

Causes to change shape and molecule released to the inside of the membrane

23
Q

What factors does simple diffusion depend on?

A
  • Concentration gradient
  • Thickness of the exchange surface
  • Surface area
  • Microvilli - increase diffusion
24
Q

With reference to the key factors that affect the rate of diffusion discussed in question one, discuss how the alveoli is adapted for efficient gas exchange.

A

– Short diffusion pathway

– each alveolus is surrounded by a dense capillary network.

-Steep concentration gradient

– dense capillary network means that blood is rapidly transported away, maintaining the concentration gradient.

  • Large surface area

– alveolar walls provide a large SA/ large SA: Volume ratio

25
Q

People who suffer from emphysema, a disease usually caused by smoking or exposure to air pollution, have a greatly reduced amount of elastin in their alveolar walls.

Why do people who suffer from emphysema often suffer from an increased rate of breathing?

A

– Destroyed elastin reduces the surface area of the alveoli

  • Destroyed elastin reduces efficiency of ventilation (higher residual volume in lungs)
  • gas exchange is less efficient - Less oxygen is transported into the blood and to the respiring tissues.
  • Increased breathing rate is required to provide sufficient oxygen
26
Q

Why would ions diffuse slowly in the cell membrane?

A

Ions and polar molecules are water soluble

centre of bilayer is hydrophobic

27
Q

What is carrier proteins used?

A

Move large molecules down their concentration gradient

different carrier proteins facilitate the diffusion of different molecules

28
Q

Why would channel proteins be moved?

A

Facilitate the diffusion of charged particles

29
Q

Why increasing channel proteins help to increase the rate of facilitated diffusion in kidney cells?

A
  • Aquaporins in a special type of channel protein allow facilitated diffusion of water through the cell membrane
  • Some kidney cells are adapted to have lots of aquaporins - allow to reabsorb a lot of water that would otherwise excreted by body
30
Q

How does a number of channel or carrier proteins affect facilitated diffusion?

A

Once all of proteins in use , faciliated diffusion can’t happen faster even if you increase concentration gradient

Increase: faster rate

31
Q

Diffusion of oxygen:

A

Simple diffusion through the cell membrane

Diffuse straight through

Random movement of oxygen molecules

down the concentration gradient

32
Q

Facilitated diffusion of glucose

A

Using carrier proteins

Attach to protein in membrane causing it change shape

Release towards opposite side of membrane

33
Q

Describe the difference between facilitated diffusion and active transport

A
  • Facilitated - use channel and carrier
  • Active - only use carrier
  • Active transport - Active process - requires ATP to move substances against the concentration gradient
  • Facilitated diffusion requires no ATP - ‘passive’ requires own kinetic energy for it
34
Q

Give two differences between facilitated diffusion and osmosis

A
  • Facilitated diffusion requires the use of channel or carrier proteins
  • Facilitated diffusion moves larger molecules compared with osmosis with molecules diffusing through the partially permeable membrane
35
Q

Explain why molecules of oxygen and carbon dioxide is able to diffuse through the membranes?

A

Small and non-polar

Use simple diffusion to diffuse through phospholipid bilayer

36
Q

Explain why ventilation of the lungs increase the efficiency of gas exchange

A

Alveoli causing the greater concentration of diffusion between alveoli and blood capillaries

37
Q

One similarity between active transport and facilitated diffusion

A

Involve transport proteins

38
Q

Give one evidence why it is entering the cell by facilitated diffusion and not diffusion

A

Concentration levels off above external concentration

39
Q

Give two functions of proteins in plasma membrane

A
  • Channel protein : Is able to transport ion/water by facilitated diffusion
  • Carrier protein helps to transport two molecules
40
Q

Exam Questions

Ventilation and Circulation of air and blood

A
  • Maintain a high concentration gradient
  • Alvelo and capillary have thin walls (‘one cell thick)
    • Reduces diffusion distance
  • Alveoli - (folded) Large Surface Area
41
Q

What do both protein channel and carrier proteins have in common?

A
  • High to low concentration
  • Specific - each molecule has its own transport protein
  • Same protein can be used for active transport (against the concentration gradient using ATP)

Topic 2B - Cell Membrane (4 decks)

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