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A-Level OCR Biology > Unit 2 - Diffusion/osmosis/active transport > Flashcards

Unit 2 - Diffusion/osmosis/active transport Flashcards

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1
Q

Define diffusion

A

The net movement of particles from an region of higher concentration to a region of lower concentration

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2
Q

Is diffusion active or passive?

A

Passive

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3
Q

Define passive transport

A

Movement of substances that does not require energy

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4
Q

Define osmosis

A

The movement of water from a region of high water potential to a region of low water potential across a partially permeable membrane

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5
Q

Define facilitated diffusion

A

Diffusion across a plasma membrane through protein channels

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6
Q

Is facilitated diffusion passive?

A

Yes

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7
Q

Is osmosis passive or active?

A

Passive

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8
Q

Define active transport

A

The movement of molecules from an area of low concentration of that molecule to an area of high concentration of that molecule. This movement requires ATP

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9
Q

What sort of molecules tend to move via diffusion across a membrane?

A
  • small molecules (e.g. gases)
  • lipid soluble molecules
  • non-polar molecules
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10
Q

How does water tend to move across membranes?

A

Through aquaporins (via osmosis)

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11
Q

Why can steroid hormones easily cross a membrane by simple diffusion?

A
  • They are lipid soluble

- They are non-polar

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12
Q

Which 2 factors affect the rate of diffusion?

A

Temperature

Concentration difference

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13
Q

What effect does an increase in temperature have on the rate of diffusion?

A

It increases the rate of diffusion

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14
Q

What effect does a greater difference in concentration of two regions have on the rate of diffusion?

A

It increases the rate of diffusion

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15
Q

Why does a higher temperature increase rate of diffusion?

A

-higher temperature means particles have more kinetic energy and move at higher speeds

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16
Q

Why is it easier for oxygen to diffuse across a membrane than water?

A
  • oxygen molecules are small and non-polar whereas water molecules are polar
  • the hydrophobic interior of the phospholipid bilayer repels the charged molecules
  • water is only partially charged so is still able to diffuse through the membrane, though only slowly
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17
Q

What 4 factors affect the rate of diffusion across a membrane?

A
  • temperature
  • concentration gradient
  • surface area
  • thickness of membrane
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18
Q

An increase in surface area of an exchange surface has what effect on rate of diffusion?

A

increases rate of diffusion

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19
Q

An increase in membrane thickness has what effect on the rate of diffusion?

A

Decreases rate of diffusion

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20
Q

Why are membranes containing protein channels selectively permeable?

A
  • Most protein channels are specific to one molecule or ion

- Therefore only these specific molecules/ions are able to move across the membrane

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21
Q

What does facilitated diffusion allow to move across a membrane?

A
  • larger molecules
  • lipid insoluble molecules
  • small charged particles
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22
Q

Give an example of a small charged particle that moves across membranes via facilitated diffusion

A

Na+

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23
Q

Give an example of a large molecule that moves across membranes via facilitated diffusion

A

Glucose or amino acids

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24
Q

What happens to carrier proteins when a specific molecule binds to them?

A

They change shape

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25
Q

How do protein channels allow charged particles to move through the membrane?

A

They provide a hydrophilic channel for charged particles

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26
Q

What are the 5 factors which affect the rate of facilitated diffusion?

A
  • temperature
  • concentration gradient
  • membrane surface area
  • membrane thickness
  • number of channel proteins
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27
Q

Which type of movement of particles requires ATP?

A

Active transport

Bulk transport

28
Q

What does active transport require to occur?

A

ATP

Carrier proteins

29
Q

Describe how active transport occurs with aid of a carrier protein

A
  • molecules/ions bind to receptors in the channel of the carrier protein
  • ATP binds to the opposite side of the carrier protein
  • ATP is hydrolysed to form ADP and phosphate
  • the phosphate molecule binds to the phosphate molecule to the carrier protein causes the protein to change shape
  • carrier protein opens, allowing molecules through
  • phosphate molecule is released and recombines with ADP to form ATP
  • carrier protein returns to original shape
30
Q

Why is active transport considered to be selective?

A

-specific substances are transported by specific carrier proteins

31
Q

Define endocytosis

A

the bulk transport of material into cells

32
Q

Define pinocytosis

A

the bulk transport of liquids into cells

33
Q

Define phagocytosis

A

the bulk transport of solids into cells, most commonly the process by which white blood cells engulf pathogens

34
Q

Define exocytosis

A

the bulk transport of materials out of a cell

35
Q

Does bulk transport require ATP?

A

Yes

36
Q

Why would a molecule be moved by bulk transport?

A

It is too big for channel or carrier proteins

37
Q

Name 3 things which are moved by bulk transport

A

Enzymes, hormones, bacteria

38
Q

Outline how phagocytosis occurs

A
  • the cell surface membrane invaginates when it comes into contact with a bacterium
  • the membrane then enfolds around the bacterium forming a vesicle around it
  • the vesicle then pinches off and moves into the cytoplasm towards lysosomes
39
Q

Outline how exocytosis occurs

A
  • vesicles are usually formed by the golgi apparatus
  • vesicles move towards and fuse with the cell surface membrane
  • contents of the vesicle are then released outside of a cell
40
Q

Name an example of exocytosis

A

Excretion

41
Q

Why are ions only able to cross a membrane through a protein channel?

A
  • protein channels provide a hydrophilic channel through the membrane
  • ions cannot pass through membranes without them due to the hydrophobic centre of the phosphoplipid bilayer
42
Q

How can the effect of surface area on the rate of diffusion be investigated?

A
  • agar made with phenolpthalein and NaOH is pink as NaOH is alkai
  • cubes of different sizes are placed in HCl
  • In HCl the cubes will go colourless
  • Leave for 5 minutes
  • measure the volume of cube that is still pink
  • calculate % diffusion
43
Q

How can the effect of temperature on the rate of diffusion be investigated?

A
  • an artificial cell is made from dialysis tubing
  • solution is placed in cell
  • cell is placed in water bath at different temperatures
  • indicators can be used to see the rate of diffusion (e.g. iodine for starch or benedict’s solution for glucose)
44
Q

What is the effect of a higher surface area to volume ratio on the rate of diffusion?

A

It increases the rate of diffusion

45
Q

What is the symbol of water potential?

A

Ψ

46
Q

What are the units of water potential?

A

kPa

47
Q

What is water potential?

A

The pressure exerted by water molecules as they collide with a membrane or container

48
Q

What is the Ψ of pure water?

A

0

49
Q

Why does water potential decrease as solute is added?

A
  • when a substance is dissolved in water the kinetic energy of the water is lowered
  • because water molecules aggregate around the solute
  • movement of water molecules is partially impeded
  • so a lower pressure is exerted
50
Q

What is a hypertonic solution?

A

having a higher concentration of solute relative to another solution

51
Q

What is an isotonic solution?

A

having the same concentration of solute relative to another solution

52
Q

What is a hypotonic solution?

A

having a lower concentration of solute relative to another solution

53
Q

What is the usual water potential in animal cells?

A

About 50kPa

54
Q

What would be the effect of placing a red blood cell in a hypotonic solution?

A
  • net movement of water into the cell
  • cell swells and bursts
  • causing haemolysis
  • cell contents lost, haemoglobin released
55
Q

What would be the effect of placing a red blood cell in a hypertonic solution?

A
  • net movement of water out of the cell
  • cell shrinks and shrivels
  • becomes darker in colour as haemoglobin is more concentrated
  • crenation
56
Q

What would be the effect of placing a plant cell in a hypotonic solution?

A
  • net movement of water into cell
  • cell becomes turgid
  • protoplast pushed against cell wall
57
Q

What would be the effect of placing a plant cell in a hypertonic solution?

A
  • net movement of water out of cell
  • contents shrink
  • cell plasmolysed
  • protoplast completely pulled away
58
Q

When a plant cell is placed in a hypertonic solution, what fills the space between the cell wall and the protoplast?

A

the external solution with a more negative water potential

59
Q

Why do plant cell walls not burst from osmosis?

A
  • they have strong cellulose walls

- which are able to resist the hydrostatic prssure

60
Q

What happens to the volume of cytoplasm when a plant cell is placed in a hypertonic solution?

A

-volume of cytoplasm decreases

61
Q

How can the concentration of a potato be determined?

A
  • weight pieces of equal size potato
  • place in different concentrations of solution
  • leave potato for the same time
  • blot potato dry and reweigh
  • calculate % change in mass
  • plot on graph
  • where line of best fit crosses 0 on x-axis shows concentration of potato
62
Q

Define precision

A

the closeness of two or more measurements to each other

63
Q

Define accuracy

A

the closeness of a measured value to a standard or known value

64
Q

Define repeatbility

A

if you repeat the experiment, how close are you results to other results you have collected

65
Q

Define reproducility

A

if someone else repeats the experiment how close are their results to yours

66
Q

Describe the routes that water molecules take through the cell surface membrane

A
  • diffuse between phospholipids

- move through aquaporins

A-Level OCR Biology (42 decks)

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