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A level OCR Biology > PAGs > Flashcards

PAGs Flashcards

1
Q

what are the health and safety risks for the osmosis PAG?

A

-take care when using the cork borer and the scalpel as they are sharp
-care must be taken when handling the ceramic tile and glassware

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2
Q

describe the procedure of the osmosis PAG

A
  1. First you need to prepare the sucrose concentrations of 1%, 0.8%, 0.6%, 0.4%, 0.2% and 0.0% e.g. 0.4%= 4ml of sucrose + 6ml of distilled water
  2. Next, prepare your 6 pieces of potato. You need to use the cork borer to remove tubes and then cut them all to the same length, ensuring that there is no peel remaining.
  3. Dry the surface of the potato pieces with kitchen roll
  4. Measure the mass of each potato piece and record this in a suitable table
  5. Place the one piece of potato into each concentration of sucrose
  6. Leave the potato pieces for 20 minutes
  7. After 20 minutes remove the pieces of potato from the solutions and dry the pieces of potato
  8. Measure the end mass of your pieces of potato and record this in your table
  9. Use the starting and ending masses to calculate the percentage change in mass of each artificial cell. Record this in your table
  10. Plot a graph of percentage change in mass against concentration of sucrose solution
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3
Q

why is it important to dry the chips and in the same way each time in the osmosis PAG?

A

to get rid of any water on the outside of the chip that could add to the mass of the potato

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4
Q

why did you compare the percentage change in mass rather than simply the change in mass of each chip?

A

This is to allow variations in size of the chips, even though attempts were made to cut them the same size. This allows for a better comparison of the results

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5
Q

What are the limitations of the osmosis PAG?

A

it doesn’t take into account that different parts of the potato may have different water potentials

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6
Q

in the osmosis PAG explain how a student could use the data of percentage change in mass to determine the water potential of the potato tuber tissue

A

The could plot a graph of concentration of sucrose against change in mass to find which concentration gives zero change in mass. When no change in mass occurs the water potential of solution is the same as the water potential of the potato. So they would look at their results table and find the concentration of sucrose solution that had no change in mass and look up the water potential of the solution on a calibration curve.

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7
Q

what are the health and safety issues with the quantitative benedicts PAG?

A

-quantitative benedicts solution contains potassium thiocyanate and potassium hexacyanoferrate
-hot liquids used
-need safe use of centrifuge procedure

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8
Q

what is the procedure of the quantitative benedicts PAG?

A
  1. make a series of 6 glucose dilutions from 1.0% to 0% in boiling tubes and label each concentration carefully
  2. Label 6 boiling tubes with an appropriate glucose concentration and a 7th ‘unknown
  3. Put 1 cm³ of the glucose concentration into the appropriate test tube and add 10cm³ of quantitative benedicts solution
  4. Boil in the water bath for 12 minutes
  5. Leave to cool
  6. Transfer liquid to centrifuge tubes and centrifuge to settle precipitate
  7. Set up colourimeter ready to take readings including setting to red filter
  8. Decant supernatant into a cuvette and read and record % transmission value for each glucose concentration including the unknown. Reset with distilled water between readings
  9. Use these known glucose concentration readings to construct a glucose calibration curve
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9
Q

quantitative benedicts PAG: what is a supernatant?

A

fluid that is left after centrifugation

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10
Q

quantitative benedicts PAG: why do we use a red filter in the colourimeter?

A

red filter absorbs blue light and reflects red light- therefore as a blue solution is being used you need a filter that will absorb that colour so that the absorbance of transmission can be measured

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11
Q

quantitative benedicts PAG: why is glucose called a reducing sugar?

A

donates electrons to copper ions- reducing them from Cu2+ to Cu+- the glucose itself is oxidised

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12
Q

quantitative benedicts PAG: explain the colour change in the benedicts solution in terms of copper ions and electrons

A

The copper (II) sulfate is a Cu2+ ion and it is reduced to copper (I) sulfate (Cu+) as it gains an electron. Copper (I) sulfate is a red precipitate solution- it gives the brick red positive result.

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13
Q

quantitative benedicts PAG: explain how the % transmission readings relate to glucose concentration

A

If there is a high concentration of glucose there are more electrons donated to the benedicts. This means more copper (I) sulfate is formed, therefore more precipitate is formed and there’s less blue solution. So, when the light of the colourimeter shines through there is more transmission which can be used to calculate concentration. The higher the transmission the higher the concentration.

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14
Q

quantitative benedicts PAG: what axis does concentration of glucose (%) go on?

A

x axis

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15
Q

quantitative benedicts PAG: what axis does transmission (%) go on?

A

y axis

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16
Q

osmosis PAG: what axis does sucrose concentration (mol dm-³) go on in the water potential graph?

A

x axis

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17
Q

osmosis PAG: what axis does water potential (KPa) go on in the water potential graph?

A

y axis

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18
Q

osmosis PAG: what axis does sucrose concentration (mol dm-³) go on in the percentage change in mass graph?

A

x axis

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19
Q

osmosis PAG: what axis does change in mass (%) go on in the percentage change in mass graph?

A

y axis

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20
Q

what are the health and safety issues with the biological molecules food tests?

A

-before carrying out the procedure, check for allergies to food chemicals
-benedicts and biuret are a mild irritant
-iodine is an irritant and a stain
-ethanol is harmful and highly flammable

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21
Q

what does iodine test for?

A

starch

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22
Q

describe the iodine test

A

add a few drops of iodine

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23
Q

what is another name for biuret solution?

A

sodium hydroxide + copper sulfate

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24
Q

what does biuret test for?

A

protein

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25
describe the biuret test
add equal volumes of solution and biuret
26
what does the emulsion test, test for?
lipids
27
describe the emulsion test
-add ethanol to solution - shake vigorously -pour into another test tube that contains water
28
what does benedicts test for?
reducing sugars
29
what are the reducing sugars?
all monosaccharides and some disaccharides
30
describe the reducing sugars test
-add benedicts in equal volumes -heat in a water bath
31
what does a clinistix test for?
glucose
32
describe the clinistix test
-dip stick in solution -compare colour
33
what is the colour change in the reducing sugars test in terms of a concentration gradient?
LOW CONC. HIGH CONC. yellow, green, orange, brown, red
34
what does the non-reducing sugars test, test for?
non reducing sugars
35
describe the non-reducing sugars test
1. add benedicts and heat in water bath (if non reducing= negative) 2. add hydrochloric acid in equal volumes to the solution 3. boil in water bath for 12 min 4. cool down 5. add sodium hydrogen carbonate powder with 1 spatula 6. add benedicts- heat in a water bath
36
in the non reducing sugars test what does adding hydrochloric acid do?
hydrolises the solution into monomers
37
in the non reducing sugars test what does adding hydrogen carbonate powder do?
neutralises the acid
38
what is the biological molecule being tested when biurets is used?
albumin
39
what is the biological molecule being tested when benedicts is used?
glucose (for reducing sugars) or sucrose (for non reducing sugars)
40
what is the biological molecule being tested when ethanol is used?
vegetable oil
41
what is the biological molecule being tested when iodine is used?
starch
42
what is the colour of bieurets solution?
blue
43
what is the colour of benedicts solution?
blue
44
what is the colour of ethanol?
colourless
45
what is the colour of iodine?
orange
46
what is the official positive colour for the biurets test?
lilac
47
what is the official positive colour for the benedicts test?
brick red (any colour change is positive)
48
what is the official positive colour for the emulsion test?
milky white
49
what is the official positive colour for the iodine test?
blue/black
50
what are some health and safety issues with the DNA extraction PAG?
-before carrying out this procedure you should check for allergies to onion and detergent -detergent is a mild irritant -protease enzyme is an irritant -ethanol is harmful and highly flammable (keep off skin)
51
what is the procedure for the DNA extraction PAG?
1. prepare the onion extract as follows: a)Add the sodium chloride to the detergent. Make up to 100 cm³ with distilled water b)Cut the onion into small pieces roughly 5 mm square. Place the pieces in a beaker, then pour on the detergent c)Stir the mixture and maintain it at 60°C in a water bath for exactly 15 minutes d)Cool the mixture in an ice water bath for 5 minutes, stirring frequently e)Pour the mixture into a liquidizer and blend for only 5 seconds on high speed f)Filter the mixture into the second beaker. Ensure that the foam on the surface of the liquid does not contaminate the filtrate. 2. Separate DNA from the onion extract: a)Add protease to the onion tissue extract in a boiling tube and mix well b)Form a layer of ice cold ethanol on top of the onion extract by pouring it slowly down the side of the boiling tube. Leave the tube for 2-3 minutes without disturbing it. Bubbles will form and whilst other compounds in the mixture dissolve, the DNA will precipitate. c)Gently rotate the glass rod in the liquid, at the interface of the alcohol and detergent mixture. Take care not to mix the layers too much or to break up the fragile DNA. The white web of mucus-like DNA can be drawn from the tube with a Pasteur pipette and re-suspended in 4% sodium chloride solution
52
what observations did you see in the addition of the protease enzyme stage in the DNA extraction PAG?
liquid turned pale green
53
what observations did you see in the precipitation of DNA using cold ethanol stage in the DNA extraction PAG?
white mucus strands appear at top of liquid
54
what observations did you see in the extraction of DNA stage in the DNA extraction PAG?
white strands attached to rod
55
DNA extraction PAG: suggest why it is necessary to cut the onion into small pieces before beginning the procedure
to create a large surface area to volume ratio
56
DNA extraction PAG: explain why the detergent breaks down cell membranes
it forms complexes around phospholipids which causes cell membranes to break down
57
DNA extraction PAG: explain why the addition of sodium chloride salt causes the DNA molecules to coalesce
sodium ions from the salt shield the negatively charged phosphate groups of the DNA molecule causing them to coalesce
58
DNA extraction PAG: describe the effect of the 60°C water bath on the DNAase enzymes
this increases the temperature of the solution
59
DNA extraction PAG: why is the use of a 60°C water bath an essential step in the procedure?
To increase the rate of reactions to unzip the double helix to separate the DNA from the proteins to cause the DNA to precipitate out to cut the DNA into fragments. If the DNAase enzymes were not denatured at this point they would being to break down the DNA into fragments.
60
DNA extraction PAG: suggest why the mixture needs to be cooled in an ice bath following heating
the cold water protects the DNA by slowing down enzymes that break it apart
61
DNA extraction PAG: explain why the mixture needs to be liquidised prior to the separation of DNA
this degrades the cell walls further, permitting release of DNA
62
DNA extraction PAG: which biological molecules would you expect to find in the filtrate after step f) of the procedure?
proteins and DNA
63
DNA extraction PAG: why must protease enzyme be added to the filtrate before separation of the DNA?
this will break down the proteins associated with the DNA in the nuclei
64
DNA extraction PAG: explain why the addition of ethanol causes DNA to precipitate from solution
ethanol pulls water from the DNA molecule so that it then collapses in on itself and precipitates

A level OCR Biology (7 decks)

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