Practicals

Question 1

Give on way in which the student could ensure the first three beetroot cylinders were kept at 25 degrees throughout her experiment (selective permeability)

Answer 1

Use a thermometer and take regular measurements throughout the experiment

Question 2

uncertainty

Answer 2

+ or - X

Question 3

how do you calculate uncertainty

Answer 3

actual reading / true value

Question 4

how can uncertainty be reduced

Answer 4

use equipment with a better resolution

Question 5

why should beetroot have the same size/length

Answer 5

so there is an equal surface area to volume ratio. This means that it wont affect the rate of diffusion e.g if there was a larger surface area more beetroot would be lost

Question 6

why should fresh beetroot be used rather than cooked beetroot

Answer 6

as the cooked beetroot will have a broken membrane so rate of diffusion will be faster

Question 7

what is the purpose of a cuvette filled with water

Answer 7

to calibrate the colorimetre

Question 8

Suggest one improvement to the design of the table and one improvement to the way she presented the data contained in the table

Answer 8

-same number of decimal places in the final column on the right
-name the solution in the first column

Question 9

suggest and explain an advantage of carrying out this investigation at 30 degrees rather than at 20

Answer 9

-At 30 degrees particles have more kinetic energy which increases the movement of particles and thus the rate of osmosis

Question 10

explain why the data in the table above are described as processed results

Answer 10

calculations have been made from raw data

Question 11

rate of reaction

Answer 11

1 / time

Question 12

how to make a control in practical measuring enzyme activity

Answer 12

replace enzyme solution with distilled water or boiled enzyme

Question 13

Enzyme activity, trypsin, milk

Answer 13

-equal volumes of trypsin and milk
-place in water bath
-record time for complete hydrolysis
-repeat at increasing temperatures

Question 14

what is the purpose of a calibration curve

Answer 14

determine the concentration of an unknown sample by comparing it to a set of values with a known concentration

Question 15

what is water potential determined by

Answer 15

-concentration of solutes
-higher solute concentration = lower water potential

Question 16

why is percentage change used

Answer 16

-potato chips may not all have the same starting mass
-easier for comparisons

Question 17

explain the change in mass of the potato chips

Answer 17

-potato with a conc lower than sucrose solution (high w.p) will loose mass

Question 18

the higher the permability

Answer 18

more pigment released

Question 19

factors affecting enzyme activity

Answer 19

-Factors affecting enzyme action = temperature, pH, concentration of enzyme, concentration of substrate

-water bath used to equilbriate

-distilled water = absense of enzyme activity

-HCL = hydrolysed sample

-IV = temperature

-DV = time for milk to be hydrolysed

Question 20

calculating mitotic index

Answer 20

-ratio of cells undergoing mitosis to the total number of cells in a sample

-must view cells under an optical microscope = living

-dye makes chromosomes visible so you can see what stage of the cell cycle are in

Question 21

calibration curve vs dilutation series

Answer 21

-calibration curves are used to determine an unknown concentration of a sample but comparing it with a standard of know concentrations

-dilution series = set of samples with known concentrations

Question 22

sucrose solution

Answer 22

Lower conc of sucrose solution = increase in mass

Higher conc of sucrose solution = decrease in mass

Question 23

aseptic techniques

Answer 23

-wipe down surface with antibacterial cleanser

-use a bunsen burner so convetion currents move away

-flame the instruments

-close doors

-larger inhibiton zone = more bacteria killed = better antibiotic works

-low inhibiton = resistance bacteria

Question 24

chromatography

Answer 24

-rate of migration of pigments depends on their solubility and affinity to the paper

-lower affinity = travel further up the paper

-more soluble = travel closer to the solvent front

-pigments further up the paper have a higher Rf value

Question 25

dehydrogenase activity

Answer 25

-dehydrogenase is an enzyme found in plant chloroplasts crucial to the LDR

-allows NADP to accept electrons so it can be reduced

-When a redox indicator dye is present, such as DCPIP, electrons are accepted by this instead. The activity of dehydrogenase can therefore be investigated using DCPIP, which turns from blue to colourless when it is reduced.

-As the light intensity decreases, the rate of photosynthesis also decreases. This is because the lowered light intensity will slow the rate of photoionisation of the chlorophyll pigment, so the overall rate of the light dependent reaction will be slower.

● This means that less electrons are released by the chlorophyll, hence the DCPIP accepts less electrons. This means that it will take longer to turn from blue to colourless.

● When the DCPIP is blue, the absorbance is higher. The rate at which the absorbance decreases can therefore be used to determine the activity of the dehydrogenase enzyme. A higher rate of decrease, shown by a steep gradient on the graph, indicates that the dehydrogenase is highly active.