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Cells Topic 2 AQA A-Level Biology > Transport Across Membranes > Flashcards

Transport Across Membranes Flashcards

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1
Q

Name the 5 ways in which substances are moved across membranes

A
  • Simple diffusion
  • Facilitated diffusion
  • Osmosis
  • Active transport
  • Co-transport
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2
Q

Define simple diffusion

A

NET movement of molecules from an area of highER concentration to an area of lowER concentration

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3
Q

What is diffusion described as?

A

A passive, random process

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4
Q

Why is diffusion described as a passive, random process

A
  • no external energy source is required (environmentally provided)
  • particles move independently from eachother
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5
Q

What is meant by the phrase “no net diffusion”

A

There is no overall change - the same number of particles are diffusing in each direction

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6
Q

Do polar molecules diffuse slowly or quickly across lipid bilayers?

A

Slowly

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7
Q

Why do polar molecules diffuse slowly across lipid bilayers?

A

Diffusion is inhibited by the NON-POLAR fatty acid tails, which repel the polar molecules

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8
Q

Which factors affect the rate of diffusion and how?

A
  • Temperature - An increase in temperature increases the kinetic energy of molecules, so rate diffusion increases
  • Concentration gradient - The greater the concentration gradient, the greater the rate of diffusion
  • Area of exchange surface - Higher area = rate of diffusion increases
  • Length of diffusion pathway - A shorter length = rate of diffusion increases
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9
Q

What is the difference between simple and facilitated diffusion?

A

Facilitated diffusion relies on the proteins present in plasma membranes

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10
Q

Why is facilitated diffusion used?

A

Because large and/or polar molecules cannot diffuse across a lipid bilayer fast enough

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11
Q

Which two types of membrane protein are involved in facilitated diffusion

A
  • Channel proteins
  • Carrier proteins
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12
Q

What is a channel protein?

A
  • Span the membrane
  • Specific (allowing certain molecules/ions to pass through)
  • Allows a specific molecule/ion to passively diffuse through
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13
Q

What is a carrier protein?

A
  • Bind with specific molecules (complementary binding site)
  • Change shape and release the molecule on the other side (the carrier changes shape)
  • Red blood cells move glucose into them in this way
  • Passive
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14
Q

What is osmosis?

A

Diffusion of a water molecule across a partially permeable membrane from an area of higher water potential to an area of lower water potential

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15
Q

What is water potential (Ψ) ?

A
  • Pressure created by water molecules.
  • Measured in kilopascals (KPa)
  • Under standard conditions of temperature and pressure (250C and 100KPa) pure water has a water potential of 0KPa.
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16
Q

What is a solute?

A

The thing that is dissolved

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17
Q

What is a solvent?

A

What it is dissolved in

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18
Q

What is a solution?

A

A solute that has been dissolved in a solvent

19
Q

How does adding solute affect water potential?

A

It lowers the water potential, meaning that water potential is negative.

20
Q

Which solution has the highest solute concentration out of -25KPa and -35KPa?

A

-35KPa

21
Q

Which terms are used to describe osmosis in animal/plant cells?

A
  • Hypotonic
  • Isotonic
  • Hypertonic
22
Q

Define Hypotonic

A
  • Less solute
  • High water potential outside the cell
  • Net osmosis into the cell
23
Q

Define Isotonic (animal/plant cells)

A
  • Same water potential on either side of the cell
  • No net osmosis
24
Q

Define Hypertonic

A
  • More solute
  • Low water potential outside cells
  • Net osmosis out of cells
25
Q

What term describes hypotonic in animal cells?

A
  • Hemolysis
  • Hemoglobin is released from cells
26
Q

What term describes hypertonic in animal cells?

A

Crenation

27
Q

What term describes hypotonic in plant cells?

A
  • Turgid
  • The water inside the cell pushes the cell out but wont burst it due to the cell wall
28
Q

What term describes hypertonic in plant cells?

A
  • Plasmolysed
  • Cell membrane pulled away from the cell wall
  • Due to water loss from the cytoplasm and vacuole
29
Q

Which formula is used to calculate the molarity/volume of a solution?

A

M1V1 = M2V2

30
Q

What does M1 mean?

A

The molarity of the stock solution

31
Q

What does M2 mean?

A

The molarity that you want

32
Q

What does V1 mean?

A

The volume of the stock solution

33
Q

What does V2 mean?

A

The volume you want

34
Q

How can this formula be rearranged to find the volume of stock solution?

A

V1 = M2V2/M1

35
Q

Define active transport

A

The movement of molecules across a plasma membrane against a concentration gradient.

36
Q

Describe the steps in active transport

A
  • Molecules travel through carrier proteins
  • Molecule binds to a carrier protein and ATP attaches to the membrane protein on the inside of the cell
  • (the ATP changes the shape of the protein in 1 direction)
  • The binding of a phosphate molecule to a the protein causes the protein to change shape
  • This means that molecules can be accessed on the inside of the cell but the membrane is closed on the outside
37
Q

How might more than one molecule be moved at the same time?

A
  • During transmission of nerve impulses
  • The sodium-potassium pump moves sodium ions out of neurons, while moving potassium ions in
38
Q

Define co-transport

A

Co-transport utilises energy in the form of an electrochemical gradient, rather than requiring the direct binding of ATP to the transport protein.

39
Q

What is another term for co-transport?

A

Secondary active transport

40
Q

What is an example of co-transport?

A

The movement of sodium ions and glucose across the lining of the small intestine (ileum)

41
Q

Describe an example of co-transport

A
  • Sodium ions are actively transported out of the epithelial cell into the blood by a sodium potassium pump i.e. active transport.
  • Sodium ions are now at a lower concentration in the epithelial cell than in the lumen of the small intestine.
  • Sodium ions now diffuse down their concentration gradient through a co-transport protein present in the plasma membrane of the epithelial cell. – Glucose is moved against its concentration gradient at the same time.
42
Q

How many sodiums/potassiums does the sodium potassium pump?

A

3 sodium ions, 2 potassium ions

43
Q

What factors affect rate of movement across a membrane?

A
  • Concentration gradient (Higher concentration gradient = faster rate)
  • Temperature (Higher temp = faster rate)
  • Surface area (Higher SA = Faster rate)
  • Length of diffusion pathway (Shorter length = faster diffusion)
  • Number of proteins (More = faster rate)

Cells Topic 2 AQA A-Level Biology (3 decks)

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