year 2 practicals

Question 1

what is the aim of chromatography experiment

Answer 1

investigate the different pigments isolated from different leaves

Question 2

method for chromatography

Answer 2

1. extract pigment from the leave
2. draw a pencil line (origin line)
3. add a drop of pigment to origin line
4. allow the drop to dry and repeat until the pigment dot is 3-5mm in diameter
5. place chromatography paper in solvent and ensure solvent is below the origin pencil line
6. when the solvent moved up the paper so that is 2mm rom the top, use forceps to take out
7. immediately draw a pencil lie to show end position of circle

Question 3

how to calculate rf value

Answer 3

distance moved by pigment/ distance moved by solvent

Question 4

why must origin line be drawn in pencil not pen

Answer 4

ink from the pen will dissolve in the solvent and run uo the paper and interfere with the results

Question 5

why should you measure the rf value from the middle of the pigment mark?

Answer 5

because the pigment mark is spread out
- so measuring from the middle standardises results
- allowing for accurate comparisons

Question 6

why should you draw a line where the solvent reaches immediately

Answer 6

the solvent evaporates rapidly, so the end position is not visible shortly after the experiment
- so if you haven’t draw the pencil line cant calculate the rf value

Question 7

why should you make sure your chromatography paper is straight

Answer 7

so the pigments move straight up the paper to avoid them running off the side of the paper and being washed off

Question 8

required practical 8

Question 9

what is the role of dehydrogenase enzymes

Answer 9

• naturally occur in the chloroplast
• catalyses the reactions involved in NADP accepting electrons from Photoionisation and photolysis of water

Question 10

What is DCPIP

Answer 10

• a redox indicator
• blue when oxidised and colourless when reduced
• it can pick up electrons from LDT instead of NADP

Question 11

ammonium hydroxide effect on DCPIP

Answer 11

• alkaline so could denature enzymes
• can also pick up electrons instead of DCPIP and NADP

Question 12

Why is one test tube covered in foil?

Answer 12

to prove decolourisation will not occur without light , electrons are leased during LDR

Question 13

how to make chloroplast suspension

Answer 13

• ice cold pH buffered isotonic solution
• filter to remove large debri
• centrifgue to obtain chlorplast

Question 14

limitations of DCPIP experiment

Answer 14

• end point is subjective: when deciding that the other test tube are the same colour as control tube
• unequal distribution of lamp- add more lamps from each angle
  -foil is not blocking out all of the light

Question 15

conclusion of DCPIP experiment

Answer 15

ammonium hydroxide does decrease the rate of dehydrogenase enzyme activity DCPIP

Question 16

Why must all solutions be ice cold?

Answer 16

when you blend the spinach and homogenising plant cell your releasing enzymes that can damage the chloroplast
- to reduce enzyme activity so they don’t damage the chloroplast

Question 17

why were spinach leabe sblended

Answer 17

to break ipen the cells and release the chlorplas

Question 18

why did you filter the blended spinach

Answer 18

to remove large pieces of cells debris ad other organelles

Question 19

why must the isotonic median be an isotonic solution

Answer 19

isotonic so ensures water potential is the same so prevents chloroplast from bursting or shrivelling

Question 20

ammonium hydroxide and other electron accepting chemicals are used as weed killers, suggest how these might kill weeds?

Answer 20

• slows the LDR
• slows ATP and NADH
• without ATP and NADPH the LIR will not occur and organic substances (glucose) will not be produced
• so the weed eventually dies

Question 21

what is the purpose of soda lime in the bottom of the test tube in respirometer experiment

Answer 21

absorb CO2 used in respiration to ensure the change is due to O2 and s the volume of O2 absorbed by the maggots can be measured

Question 22

how does the respirometer experiment work?

Answer 22

• respiring maggots or whatever organism in one tube, glass beads in another (control)
• O2 diffuses into maggots to be used in aerobic respiration, CO2 diffuses out and is absorbed by soda lime
• SO volume of gas and pressure decreases in maggots tube
• pressure is higher in control tube therefore the red liquid moves towards the experimental tube

Question 23

how to measure the rate in respirometers

Answer 23

volume= πr^2h
rate= volume/ time x mass

Question 24

why must apparatus be air tight in respirometer

Answer 24

prevent air entering or leaving as this would change the volume and therefore the pressure which effects the movement of the colour liquid

Question 25

what side would the liquid move to

Answer 25

- towards the experimental tube - respiring maggots take in O2 from the air in experimental tube and CO2 is absorbed by soda lime - vol of gas decreases and pressure decreases - pressure is higher in the control tube so coloured liquid moved towards experimental tube

Question 26

unit for volume per unit time per unit mass

Answer 26

cm^3 min^-1 g^-1

Question 27

what is TTC and how is it used in the yeast experiment

Answer 27

- TTC is a redox indicator - colourless when oxidised and turns red when reduced - it can accept (pick up) hydrogen when removed by dehydrogenase in respiration

Question 28

importance of dehydrogenase in yeast practical

Answer 28

- naturally occurs in yeast - catalyses the reactions involved in removing H from coenzymes - involved when NADH is made and were NADH is reoxidised into NAD

Question 29

hypothesis for yeast experiment

Answer 29

the yeast and TTC will turn red faster, indicating a rate of reaction, as the temperature increases

Question 30

limitations of yeast experiment

Answer 30

- end point is subjective - difficulties in seeing colour change in the water bath

Question 31

why must both solutions be kept in a water both for 5 in before the reaction

Answer 31

so the yeast and TTC both equilibrate to the test temperature

Question 32

why did the TTC turn red?

Answer 32

Dehydrogenase removed from H from NADH and TTC picked up this H - so this reduced TTC so it formed a red preiticipate

Question 32

at which stages of respiration will dehydrogenase be removing hydrogen?

Answer 32

- NADH is made in glycolysis, link rection and the krebs cycle

Question 33

a null hypothesis for woodlice stimulus experiment?

Answer 33

there is no difference in the no. of invertebrates that turn to the light or dark side of the maze

Question 34

what is the purpose of the control maze

Answer 34

to show the difference in movement within the maze due to independent variable

Question 35

why is it important to repeat with at least 10 maggots

Answer 35

so the mean and statistic can be calculated to see if the difference in turning direction is significant or due to chance

Question 36

after each maggot has moved along the maze you are asked to wipe the maze with cotton wool. why?

Answer 36

- maggots leave a trail of chemicals where they move which could influence the choice other maggots make

Question 37

explain why most invertebrates move to the dark and humid chamber

Answer 37

- humid environment is advantageous as it helps prevent drying out - dark environment is advantageous as it is harder for predators to locate

Question 38

difference between the maze and the circular wheel

Answer 38

maze is kinesis wheel is taxes

Question 39

glucose in urine sample

Answer 39

use benedict's solution use calorimeter ]to plot calibration curve

Question 40

how can sampling accurately represent the population

Answer 40

- random: sampling in uniform areas to avoid bias - line transects: to examine a change over distance - large number of samples (30+)