PAGS

Question 1

Biuret test
What does is test for?
What do you do if the sample is coloured and incompletely dissolved?
what can a control be?

Answer 1

test for proteins
as it can be hard to see the colour change if the test solution is mixed fully with the sample, it can be easier to see a colour change if the test solution is layers on the sample and looking for a colour change at the interface where they touch- buret agent slides down at 45* angle . can shake to mix it after
distilled water into of protein suspension
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Question 2

How does the emulsion test work?

Answer 2

dissolve any lipid present in ethanol. let any solid settle at the bottom then pipette the ethanol into a new tube
then add water causing it to precipitate out and form an emulsion
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Question 3

Benedicts test for reducing sugars:

Answer 3

record observations with Benedict’s reagent
record observations after 2 mins in water bath
record observations after another 2 mins in water bath

Question 4

Benedict’s test for non reducing sugars:

What are the observations?

Answer 4

carry out reducing sugar test
if negative add HCl
put in water bath for 2 mins
let them cool
neutralise acid with sodium hydrogen carbonate until no more effervescence
repeat neutralisation until pH is 7 or higher
add Benedict’s reagent and record observations
record observations after 2 mins of water bath
record observations after 2 more minutes of water bath

if there are more copper 2+ ions reduced to copper then the solution will be less blue (more colourless) therefore more red light is transmitted (less absorbed)

Question 5

How can the Benedict’s test be improved?
How could you make it semiquantitative?
How could you make it fully quantitiave?
How would you distinguish between maltase and glucose?

Answer 5

pH probe
graduated glass pipette for volume fo solution and benedicts
repeat

look at speed of colour change
have standard colour to compare against
more precipitate= more reducing sugar so weigh mass

colorimeter

once hydrolysed, the maltose will have 2x the amount fo glucose so twice the amount of precipitate/ more concentrated

Question 6

How do you determine glucose concentration using a colorimeter?
Why must you centrifuge the sample before taking colorimeter readings?
What would you do if the unknown didn’t fall within readings?

Answer 6

do serial dilution
add Benedict’s reagent to each tube plus an unknown
incubate for 15 minutes
put 2cm3 in centrifuge for 2 minutes ensuring each tube has a balancing partner
set colorimeter to red light and use distilled water in a cuvette to set 100% transmission
pipette supernatants into cuvettes and measure transmission %
create calibration curve to find unknown

solid precipitate could affect transmission readings as it would cause light rays to scatter and give falsey low reading

repeat but start at higher concentrations if unknown is too low transmission

Question 7

colorimeter

Answer 7

in folder

Question 8

How do you do a serial dilution?

Answer 8

10cm3 graduated pipette to draw up 10cm3 of solution to first tube
now take 1cm3 pipette and add 1cm3 of first dilution to the second tube. add distilled water to make up to 10cm3 and shake - concentration is 10-1 of original
use clean pipette draw up 1cm3 of the second dilution and add to tube 3 and make the solution up to 10cm3 with distilled water and mix.
repeat.

Question 9

effect of substrate concentration on rate of enzyme controlled reaction:
what is the word equation? why do cylinders need to be the same size?
What are the limitations and how can they be overcome?

Answer 9

do serial dilution with hydrogen peroxide
add 5cm long potato cylinders to conical flask with hydrogen peroxide - catalase enzyme
add bung and measure volume of oxygen produced in.a measuring cylinder and water trough very 30 secs for 3 minutes
calculate mean and standard deviation for each concentration and rate of gas production

hydrogen peroxide + catalase - oxygen + water
same SA of catalase

catalase concentration wast controlled exactly - measure SA
temperature could have changed so use water bath
mark

Question 10

Investigating affect of temperature on enzyme activity- what observations will you see?

Answer 10

once all starch has been broken down by amylase the iodine will no longer change colour
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Question 11

Affect of enzyme concentration on ROR:

Answer 11

create serial dilution with trypsin (protease enzyme)
add milk powder to each and time how long it takes for writing to become visible
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Question 12

Affect of temperature on membrane permeability

Explain results

How does ethanol affect permeability?

Limitations of procedure?

Answer 12

warm distilled water in water baths of different temperatures
cut 5mm beetroot cylinders and rinse and pat dry
add them to water baths for 15 mins
swirl once then remove cylinders
poor liquid in cuvette
use colorimeter to measure absorbance (AU) arbitrary units

absorption increases slowly until 40* as little pigment (beta cyanins) leaks out tonoplast
Then it increases rapidly as phospholipids gain kinetic energy so gaps appear as fluidity increases. phospholipids melt and proteins denature at 50*
levels of at 60* when membrane can’t break much more

dissolve membrane as phospholipids dissolve so permeability increases a lot. cholesterol also dissolves even though its meant to maintain membrane

beetroot not accurately cut- different SA, no of cell exposed so amount fo pigment
different beetroots was he and dried different amounts
beetroot varies with age and type, different areas of beetroot
took time to get out and put in cuvettes so some were in longe the others

Question 13

investigating osmosis in an artificial cell
why do you compare % mass not change in mass?
why are they not comparable to real cells?
What other solutions could be used?

Answer 13

cut dialysis tubing the same length and tie it
fill them all with 0.4moldm-3 sucrose solution
tie knot at other end
weigh them
place them all in different concentration sucrose solutions and reweigh after 20 mins
blot any excess solution from outside the cell
calculate % change in mass

may have started at different masses even if lost the same amount so not comparable

don’t have phospholipid bilayer and carrier or channel proteins
do have selectively permeable membrane but is depending on size of molecule
no active transport as no ATP

salt solutions, protein solutions, more intervals, water

Question 14

What does standard deviation show?

Answer 14

o Measurement of variability
o Shows how much variation there is from the mean or expected value
o A low standard deviation indicates that the data points tend to be very close to the mean
o A high standard deviation indicates that the data are spread out over a large range of values
o Useful in comparing data with the same mean but with a different range

word doc??

Question 15

How do you calculate standard deviation?

Answer 15

1. Calculate the mean of the sample
2. Subtract the mean from each value of X to calculate the difference between the value and the mean
3. Square each difference to remove any negative values
4. Calculate the sum of all the squared differences
5. Divide the sum by the degrees of freedom (df) which is the total sample size minus 1 (n-1)
6. Take the squared root to calculate the standard deviation for the sample

Question 16

Reproducible

repeatable

Answer 16

someone else

yourself

Question 17

Anomalies-
mean- 
precision- 
what axis does independent and dependent variable go on?
valid?
Don't say-

Answer 17

identify
calculate
equipment

only change independent variable
average, reliable, amount

Question 18

How do you control and monitor the following factors:
temperature
control:
monitor:
pH
control:
Monitor:

Answer 18

thermostatically controlled water bath
thermometer
buffer
indicator, pH probe

Question 19

What are error bars?

Answer 19

o The error bars shown in the line graph represent a description of how confident you are that the mean represents the true impact energy value.
o The more the original data values range above and below the mean, the wider the error bars and less confident you are in a particular value.
o the part of the error bar above each point represents plus one standard error and the part of the bar below represents minus one standard error.

Question 20

Affect of SA to vol ratio on diffusion rate:
What factors need to be controlled?
How could you make more accurate?
What are the limitations compared to living organisms?

Answer 20

agar cubes of different sizes
immerse tubes in HCl
time how long it takes pink to dissapear

volume of HCl
same type of agar
same temperature

repeat at least twice and take an average

not agar or cube 
hard to cut and measure accurately 
hard to maintain constant shape 
end point hard to see with eye
if blocks float then not completely submerged to diffusion rate affected

Question 21

Mitosis in garlic roots:

Answer 21

put HCl and tolvidinc stain into water bath at 60* and wait to get to that temperature
slice off bottom of garlic with the roots and place in water bath for 5 mins
remove and rinse with distilled water
cut root tips an leave in water bath for 5 mins too (with HCl?)
remove a root tip and put on clean microscope slide, add stain then coverslip
wearing latex glove, place filter paper to absorb excess stain
should see various stages of mitosis in cells near root tip in microscope
?????

Question 22

light microscope to study mitosis
why are cells not resting in interphase?
Why would roots be good to look at?
what were most of the cells in?

Answer 22

place slide on stage
use focusing dial to move stage so slide is about to touch lense
use coarse focusing dial to focus down until cells ate clear to see
make sure cells are in centre of the field of view (circle of light)
rotate medium power lease until chromosomes are visible
rotate high power lease and fine focusing dial to bring chromosomes into distinct view
use eyepiece graticule to measure length of chromosomes

still functioning and carrying out normal functions, growth etc.

growing so have high mitotic index so lots of cells will be undergoing mitosis

interphase as longest

Question 23

what is 1 EPU at:
x40
x100
x400

Answer 23

25um
10um
2.5um

Question 24

affect of substrate concentration on catalase activity
explain the observations?
limitations and overcoming them?

Answer 24

serial dilutions of hydrogen peroxide
place celery extract into a watch glass and soak discs of filter paper in it for 5 mins
drop into hydrogen peroxide solution and use a clean glass rod to push it to the bottom
time how long it takes for the disk to reach surface
refresh celery extract every 3 disks and repeat for other concentrations of hydrogen peroxide

as concentration increases time taken decreases because the catalase in the celery broke down the hydrogen peroxide producing oxygen which caused it to rise. the higher the concentration the more substrate so more ESC can form at once so higher ROR- more oxygen produced

human error when starting stop clock- same person timing
disks soaked for more or less than 5 minutes

mark

Question 25

what is dilution factor?

Answer 25

volume added/ total volume. then you x by previous answer for concentration for serial dilutions

Question 26

DNA isolation from fruits

What step did we skip?

Answer 26

peel fruit and cut into chunks then place in blender- break cell wall to release DNA through lysis
add 250ml lysis buffer ??
Homogenize for 5 seconds on high until no large chunks left- iff too much then it will shear the DNA too much and it won’t spool well
slowly poor homogenate through cheesecloth into a large beaker
measure 10ml of filtrate into a beaker
add 1ml of detergent and stir well- dissolve fats and denature proteins in cell membranes
pour 20ml of ice cold ethanol down the side of the beaker and the alcohol should form a layer on top of cell lysate as its insoluble - ??
let it sit for 203 minutes without disturbance. bubbles will form and DNA will precipitate as long stringy fibres out of the solution at the interface- DNA is soluble in water but insoluble in alcohol
gently spool on a wooden applicator stick. in lab would collect my mass centrifugation.

purification- once cells are broken open the cellular contents are mixed together so to remove proteins from nucleic acids, RNA, and inactivate enzymes which break down DNA. may be done with heat, chemicals, organic solvents like phenol or protein digesting enzymes.
mark

Question 27

Gas exchange and ventilation in bony fish:
Which part of the mouth moves?
what does the operculum feel like?
what colour are the gills?

Answer 27

the bottom
smooth, hard, tough
How many gills are there?
red (feathers) due to capillaries and blood

Question 28

Method for potometer:
Why do you need an airtight seal?
What are the limitations and how do they affect the data?
How could you reduce the limitations?

What must you always talk about

Answer 28

1. lay the capillary tube and rubber connecter underwater and fill both parts
2. pick a shoot with a stem diameter similar to rubber connector and keep end of shoot underwater whilst you cut it
3. insert shoot into rubber connector underwater
4. clamp capillary tube to stand with shoot at top end and place the bottom end of capillary tube into a beaker of water
5. smear vaseline around the joint between shoot and rubber connector to ensure airtight seal
6. leave apparatus for 5 mins to allow water to be drawn into end of capillary tube and form a small air bubble
7. if no air bubble the tube can be removed from water and a piece of paper towel use to soak a little water from the end of the capillary tube so when its put back in water a small bubble should appear
8. time movement of air bubble along capillary tube for set distance. repeat and calculate mean.
9. reset bubble to start by repeating step 7. repeat at different environmental conditions

The control variables- temp, air movement and light and how they will be controlled. also about panel of water to reduce heat from light

Question 29

Method for transverse sections:

Answer 29

1. obtain a stick of celery about 5cm long
2. rest horizontally on white tile and cut perpendicularly using a blade to create thin transverse sections
3. use forceps to put them in a small beaker with tap water and leave for 2 mins
4. use a stage micrometer to calibrate eyepiece graticule for x4 and x10 objective lens
5. lift transverse sections out of water using forceps and put on a watch glass containing toluidine blue for 1 minute
6. using forceps lift the back into tap water to rinse off excess stain
7. put it on a microscope slide and add a drop of tap water and a coverslip. repeat for 3 thinnest transverse sections
8. view under 4x objective lens and find the clearest view that shows a variety of structures and produce a scientific drawing
9. view under higher magnification x10 objective lens to find the clearest view of a vascular bundle, and produce a scientific drawing

Question 30

What colours does Toluidine blue turn:
xylem
phloem
sclerenchyma
collenchyma
parenchyma

Answer 30

green or blue green (lignified)
red (non lignified)
blue green
red purple
red purple

Question 31

Method for longitudinal sections:
Why is is important to produce very thin slices of plant tissue?
Why is it important that the structures are truly transverse of longitudinal and not cut at an angle?
What is the nest way to get the sections as thin as possible?
Why are stains useful in microscopy?
Why is Toluidine blue useful for this protocol?

Answer 31

1. take remaining celery stem and cut of thin perpendicular slice to remove dried end
2. make another perpendicular cut to make stem 2cm long
3. cut stem in half lengthways
4. using a blade cut very thin slices lengthways (longitudinal sections) of one of the split halves starting from the inner surface
5. use forceps to lift into a beaker of water for 2 mins, then a watch glass with toluidine blue stainer 1 minute, then water to remove excess stain
6. put on microscope slide and then add a drop of tap water and a coverslip
7. view under lowest magnification and find a view of a variety of structures and draw a scientific drawing
8. view under highest magnification and draw a vascular bundle

low hazard