1
Q
how can valid results be obtained with a potometer?
A
- use a healthy, fresh plant shoot
- cut plant shoot and assemble potometer underwater (avoid air bubbles)
- dry leaves (control humidity/initial Ψ around leaves)
2
Q
how to prepare a photosynthetic pigment extract? (and why)
A
- soak leaves in acetone (propanone) to act as a solvent
- add a pinch of sand (help grind)
- use a mortar and pestle to grind up leaves with acetone
3
Q
stationary phase in TLC
A
silica gel layer of TLC plate
4
Q
what solvent is used for photosynthetic pigment TLC?
A
- cyclohexane
- propanone (acetone)
- petroleum ether
5
Q
why must a lid be used on TLC?
A
- solvents are volatile
- evaporate quickly
- will not diffuse up the TLC plate and carry extract
6
Q
how and why must you be careful when handling TLC plates?
A
- avoid fingerprints
- avoid damaging fragile silica gel layer
7
Q
why must the TLC plate not touch the sides of the beaker/tube?
A
- solvent may evaporate off the plate, condense and drip down the side of the container
- can damage the silica gel
- can skew the movement of solvent (making it hard to measure Rf values)
8
Q
how can photosynthetic pigments be identified from TLC?
A
- measure Rf values and record colours
- compare to known data
9
Q
what can be used to add sample spots to TLC and why?
A
capillary tube for small spots
10
Q
how many spots should be applied in TLC?
A
- multiple (3/4) spots of EACH sample in the SAME spot (concentrated pigment)
- if using different samples, spot them in different places
11
Q
what is a TLC plate placed in?
A
developing chamber (tall beaker with lid)
12
Q
how can solvent evaporation be reduced in a developing chamber?
A
- add a lid
- place a layer of filter paper around inner walls of developing chamber, wet the filter paper with solvent to adhere to the sides of the chamber and saturate it (prevent solvent from TLC evaporating and condensing on the side of the chamber)
13
Q
how does the solvent travel through TLC?
A
capillary action
14
Q
why must the TLC plate be taken out before the solvent reaches the top?
A
- once the solvent reaches the top, Rf values may be invalid
- pigments may start to run into each other (ones at the bottom catch up with the ones at the top etc)
15
Q
why must you mark the solvent front immediately with a pencil?
A
- avoid solvent evaporating (will no longer be able to see the solvent front)
- pencil to avoid interference with the pigments and damage to the silica gel
16
Q
how are molecules separated in TLC?
A
- relative adsorption with the stationary phase
(separated by polarity depending on the solvent: polar molecule in polar solvent will spend less time adsorbed to the stationary phase)
17
Q
potential limitations of a respirometer
A
- measurements may only be taken at big intervals
- apparatus may not be air tight
- may be difficulty reading meniscus leading to inconsistent, invalid results
- may not be a scale on the capillary tube
18
Q
what should you make sure to do whenever varying or controlling temperatures?
A
allow things to equilibrate (e.g. test tubes of water to equilibrate with the surrounding water bath temperature)
19
Q
before placing beetroot cubes/cores in varying solutions what should you do? and why?
A
- wash them in distilled water to allow any excess pigment that has already leaked out of damaged cells to wash off
- improves validity and ensures results are comparable as each beetroot piece started at the same point
- blot the beetroot cells dry to remove excess water and pigment
20
Q
how and when do you calibrate a colorimeter?
A
- use a cuvette of distilled water and “zero” the colorimeter
- between every sample
21
Q
what filter do you use for colorimetry? and what does the % absorbance mean? use an example
A
- opposite colour to the thing you are testing
- higher % absorbance means there is more of the coloured pigment
- e.g. for beetroot solutions, use a blue filter because red absorbs blue light. higher % absorbancy means more red pigment
22
Q
how should you label a petri dish?
A
- initials
- date
- microorganisms growing
- write on the base of the petri dish
23
Q
four pre-inoculation aseptic techniques in microbiology PAG
A
- sterilise surfaces
- wash hands with soap
- don’t touch any sterile equipment
- sterilise equipment with ethanol and flaming
24
Q
how do you make an agar plate using molten agar and a culture broth?
A
- flame the neck of the molten agar bottle and the culture broth bottle
- use a sterile pipette to transfer a certain volume of the culture into the molten agar and replace the lid
- roll the bottle of bacteria and agar to mix the solution without frothing it
- flame the neck of the bottle again
- lift the petri dish lid at an angle
- pour the bacteria agar solution into the petri dish
- replace the lid
25
why do you place the petri dish upside down?
- avoid dehydration
- avoid condensation on the lid dripping down onto the agar
26
why don't you put tape around the whole lid to seal petri dishes?
to leave gaps for air to get into petri dish so bacteria can respire
27
how can you ensure comparable results?
- make sure variables are controlled
- take measurements before and after
- calculate % changes
28
what should you do to the potato cubes/cores before reweighing them?
blot them dry to remove excess water that hasn't diffused into the cells via osmosis
29
what solutions should be used when investigating the water potential of potatoes?
proportional dilutions of sucrose solution
30
original colour of Benedict's solution
blue
31
what MUST you do before carrying out a non-reducing sugar test?
carry out a reducing sugar test and get a negative result
32
colour change of a test for protein
blue to lilac
33
non-reducing sugar test
- test negative for reducing sugars first
- boil with dilute HCl
- heat with Benedict's solution at 85°C for 5 minutes to get a positive result
34
seven inoculating aseptic techniques in microbiology PAG
- work near a bunsen burner
- dispose of used disposable equipment in a disinfectant such as vircon
- keep lids on whilst not in use
- lift lids at angles
- flaming necks of bottles/equipment
- soak equipment in ethanol + flame
- resterilise equipment between every use
35
four post-inoculation asperic techniques in microbiology PAG
- sterilise all equipment
- dispose of equipment in disinfectant
- sterilise work surfaces with disinfectant
- wash hands with soap
36
why are aseptic techniques important even when using harmless strains?
- mutations can occur
- microbiome may be contaminated
37
how can you use standard deviations to determine the chance that there is a significant difference in two means?
- if SD overlap, there is less chance of a significant difference
- a t-test should still be used to confirm
38
precision vs accuracy
- precision is how close values are to values from a different set of results
- accuracy is how close values are to the "true" value
39
why shouldn't you work with bacteria above certain temperatures?
it might encourage growth of human pathogens
40
how do repeats improve experiments?
- anomalies can be identified and ignored
- means, SDs and stats tests are more accurate (anomalies ignored)
- reduce impact of anomalous results
- more repeatable and reproducible
Biology
flashcards
Decks in class (33)
# Cards
-
Transport in Plants53
-
Enzymes25
-
Diseases10
-
Ecosystems42
-
Types of proteins8
-
Classification and Evolution22
-
Nitrogen cycle8
-
Hormonal control46
-
Variation and Evolution24
-
Excretion111
-
Random6
-
Gas Exchange29
-
Transport in animals50
-
Animal responses106
-
Biodiversity116
-
Genetics of living systems83
-
Exam tech38
-
Respiration45
-
Photosynthesis14
-
Manipulating genomes57
-
Immune response109
-
Neuronal communication53
-
Statistics16
-
Cell division36
-
Microscopy and cell structure52
-
Biological molecules15
-
Homeostasis34
-
Muscles2
-
Cloning and Biotech166
-
Practicals40
-
Plant Hormones66
-
Patterns of Inheritance48
-
Populations and Sustainability2
