Practicals Flashcards
(72 cards)
1
Q
Give on way in which the student could ensure the first three beetroot cylinders were kept at 25 degrees throughout her experiment (selective permeability)
A
Use a thermometer and take regular measurements throughout the experiment
2
Q
uncertainty
A
+ or - X
3
Q
how do you calculate uncertainty
A
actual reading / true value
4
Q
how can uncertainty be reduced
A
use equipment with a better resolution
5
Q
why should beetroot have the same size/length
A
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
6
Q
why should fresh beetroot be used rather than cooked beetroot
A
as the cooked beetroot will have a broken membrane so rate of diffusion will be faster
7
Q
what is the purpose of a cuvette filled with water
A
to calibrate the colorimetre
8
Q
Suggest one improvement to the design of the table and one improvement to the way she presented the data contained in the table
A
-same number of decimal places in the final column on the right
-name the solution in the first column
9
Q
suggest and explain an advantage of carrying out this investigation at 30 degrees rather than at 20
A
-At 30 degrees particles have more kinetic energy which increases the movement of particles and thus the rate of osmosis
10
Q
explain why the data in the table above are described as processed results
A
calculations have been made from raw data
11
Q
rate of reaction
A
1 / time
12
Q
how to make a control in practical measuring enzyme activity
A
replace enzyme solution with distilled water or boiled enzyme
13
Q
Enzyme activity, trypsin, milk
A
-equal volumes of trypsin and milk
-place in water bath
-record time for complete hydrolysis
-repeat at increasing temperatures
14
Q
what is the purpose of a calibration curve
A
determine the concentration of an unknown sample by comparing it to a set of values with a known concentration
15
Q
what is water potential determined by
A
-concentration of solutes
-higher solute concentration = lower water potential
16
Q
why is percentage change used
A
-potato chips may not all have the same starting mass
-easier for comparisons
17
Q
explain the change in mass of the potato chips
A
-potato with a conc lower than sucrose solution (high w.p) will loose mass
18
Q
the higher the permability
A
more pigment released
19
Q
factors affecting enzyme activity
A
-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
20
Q
calculating mitotic index
A
-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
21
Q
calibration curve vs dilutation series
A
-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
22
Q
sucrose solution
A
Lower conc of sucrose solution = increase in mass
Higher conc of sucrose solution = decrease in mass
23
Q
aseptic techniques
A
-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
24
Q
chromatography
A
-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
25
dehydrogenase activity
-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.
26
repeating an experiment=
makes the data reliable
27
describing a graph
-rapid increase, steady increase, levels off
-split the graph into sections and describe them
28
small sample =
data is not representative
29
why can oxygen production be used a measure of metabolic rate
-oxygen is used in respiration which provides energy
30
why is a log scale used
large range of numbers
31
why is a layer of oil used in this experiment
prevents oxygen entering
32
what is the purpose of chromatography
to separate out different pigments according to their solubility in a particular solvent
33
when would you use a colorimeter
when the endpoint of a reaction has a colour change and you need to convert this into a quantitive measurement
34
example of method limitations
subjective end point
water bath was not thermostatically controlled
test of pH range wasnt wide enough
35
why only use the first 5mm tip of an onion
thats where the cells undergoing mitosis are
36
why do you press firmly down on the cover slip
to get a thin layer of cells so light can pass through
37
use of stain when investigating mitosis
to make chromosomes visible
38
potometer
investigate the effect of environmental factors on rate of transpiration
cut shoot underwater to prevent air entering the xylem
place shoot in tube
dry the leaves of the shoot
allow singular air bubble to form and record it starting location
further the bubble travels = faster the rate of transpiration
39
using a colorimeter
use red filter for beneditcs test
less red light absorbed = more glucose reacted
prepare a whole range of solutions with a known concentration (stock solution)
e.g test tube 1 has 5cm3 glucose solution and test tube 2 has 4cm3 glucose and 1cm3 water
react each of these solutions with benedicts
and use colorimeter/zero colirmeter with distilled water
Draw calibration curve
plot concentration over absorbance
40
absorbance factor is too great =
dilute the solution
41
use of light microscope at high power and low power, including use of a graticule
light microscope = smaller organelles like ribosomes are not visible
electron microscope = cannot view living organisms
SEM = 3D image, TEM = 2D image
if scale bar given = measure scale bar to get image size
scale bar = actual size
42
eyepiece graticule
-use stage micrometer to calibrate the eyepiece graticule
-count how many divisions on eyepiece graticule fit into one division on the micrometer scale
-use this to work out magnification
eyepiece graticle is found in the eyepiece lens of an optical microscope
microscope needs to be calibrated using eyepiece graticle, to measure the size of object being viewed
calibrated in combination with stage micrometer
43
Drawing scientific diagrams
Rules for biological drawings:
The drawing must have a title
The magnification under which the observations shown by the drawing are made must be recorded
A sharp HB pencil should be used (and a good eraser!)
Drawings should be on plain white paper
Lines should be clear, single lines (no thick shading)
No shading
The drawing should take up as much of the space on the page as possible
Well-defined structures should be drawn
The drawing should be made with proper proportions
Label lines should not cross or have arrowheads and should connect directly to the part of the drawing being labelled
Label lines should be kept to one side of the drawing (in parallel to the top of the page) and drawn with a ruler
44
equipment for measurements
mass: weighing balance
time: stop watch
volume: measuring cylinder
temperature: thermometer
length: 100cm ruler
45
apparatus to measure pH
pH probe
46
why is a volummetric flask more effective for making solutions
has a calibrated marking so the volume can be measured.
designed to hold a specific volume, top is narrow to prevent spillage and the bottom of the flask is round so solution/solute is well distrubuted
47
safely and ethically use organisms to measure:
plant or animal responses
physiological functions
When using live animals in biological experiments, care must be taken to avoid harming them.
For example, aquatic animals should only be observed for a short time before being promptly returned to their main container.
It is generally thought that it may be necessary to use laboratory animals in some cases in order to create improvements for people, animals or the environment
48
chromatography practical
1. Draw a straight line in pencil approximately 1cm above the bottom of the filter
paper being used. Do not use a pen as the ink will obscure the results.
2. Cut a section of leaf and place it in a mortar. Add 20 drops of acetone and use
the pestle to grind up the leaf sample and release the pigments.
3. Use a capillary tube to extract some of the pigment and blot it onto the centre
of the pencil line you have drawn.
4. Suspend the paper in the solvent so that the level of the liquid does not lie
above the pencil line and leave the paper until the solvent has run up the paper
to near the top.
5. Remove the paper from the solvent and draw a pencil line marking where the
solvent moved up to. The pigment should have separated out and there should
be different spots on the paper at different heights above the pencil line.
6. Calculate the Rf value for each spot (distance travelled by solute/distance
travelled by solvent). Always measure to the centre of each spot.
49
Affinity + solubility
1. Affinity- pigments have different affinities to the chromatography paper; those with
lower affinities will travel further up the paper.
2. Solubility- pigments that are more soluble travel faster up the paper and will end up
closer to the top at the solvent front.
travel further up the paper = large Rf value
50
gel electrophoresis = separate proteins/DNA fragments
Of the electrical charge molecules carry – positively charged molecules will move towards the cathode (negative pole) whereas negatively charged molecules will move towards the anode (positive pole) eg. DNA is negatively charged due to the phosphate groups and so when placed in an electric field the molecules move towards the anode
Different sized molecules move through the gel (agarose for DNA and polyacrylamide – PAG for proteins) at different rates. The tiny pores in the gel result in smaller molecules moving quickly, whereas larger molecules move slowly
Different restriction enzymes cut the DNA at different base sequences. Therefore scientists use enzymes that will cut close to the variable number tandem repeat (VNTR) regions
Variable number tandem repeats (VNTRs) are regions found in the non-coding part of DNA. They contain variable numbers of repeated DNA sequences and are known to vary between different people (except for identical twins). These VNTR may be referred to as ‘satellite’ or ‘microsatellite’ DNA
The smaller mass / shorter pieces of DNA fragments will move faster and further from the wells than the larger fragments
The fragments are not visible so must be transferred onto absorbent paper or nitrocellulose which is then heated to separate the two DNA strands
Probes are then added, after which an X-ray image is taken or UV-light is shone onto the paper producing a pattern of bands which is generally compared to a control fragment of DNA
Probes are single-stranded DNA sequences that are complementary to the VNTR regions sought by scientists. The probes also contain a means by which to be identified. This can either be:
A radioactive label (eg. a phosphorus isotope) which causes the probes to emit radiation that makes the X-ray film go dark, creating a pattern of dark bands
A fluorescent dye (eg. ethidium bromide) which fluoresces (shines) when exposed to ultraviolet (UV) light, creating a pattern of coloured bands
51
Aseptic techniques
Wipe down surfaces with antibacterial cleaner, both before and after
experiment.
● Use a Bunsen burner in the work space so that convection currents draw
microbes away from the culture.
● Flame the wire hoop before using it to transfer bacteria.
● Flame the neck of any bottles before using them to prevent any bacteria
entering the vessel (air moves out so unwanted organisms don’t move in).
● Keep all vessels containing bacteria open for the minimum amount of time.
● Close windows and doors to limit air currents.
52
Response to evaluations questions
Evaluating the method:
-comment on sample size = larger sample size is more representative
-type of people used in the sample = same age/sex/lifesyle/BMI etc
-whether animals or humans are used in the sample
-time and duration of the experiment = longitudinal = can view long term effects
-placebo or not
-repeats + calculated mean
-randomly assign ppts = removes bias
-mention control variables
Evaluating the data:
-always state the overall trend relating to the axis
-is there any overlap in data
-is the test group different from the control group
-is there a statistic
-always used data evidence for these type of questions
Evaluating the conclusion:
-talk about the correlation
-use of statistical test to determine the signifiance of reuslts
-analysis the data = enough evidence to support the conclusion
-overlap in SD or not
-how large the differences in data are
-repeated or not = affects reliablity
53
area of inhibition zone equation
A = Pi x d^2 / 4
54
incubation temperature of bacterial sample
: Bacteria sample is incubated at 25°C. This is because incubating at 37°C (human
body temperature) could enable pathogens to grow that are harmful to humans.
55
larger inhibiton zone
● If there is a larger inhibition zone around the antibiotic, it has killed more
bacteria. Therefore, the larger the inhibition zone, the better the antibiotic works.
● Some antibiotics will have no/very little inhibition zone. This shows that the
bacteria are resistant to this antibiotic and are not killed by it.
56
cell membrane permeability
Cell-surface membranes are made up of a phospholipid bilayer which makes them
selectively permeable. This permeability can be changed by different variables, such
as temperature and concentration of solvents, like ethanol.
The permeability of a membrane can be measured by using beetroot cells, which
contain a purple pigment called betalain. When the cell-surface membrane has a
higher permeability, more pigment leaks out of cells. The permeability can therefore be
measured by the amount of pigment leaked from beetroot cells into an aqueous
solution using a colorimeter.
57
precuations
cut using scalple away
disinfect/wash hands with soap
keep glass beakers away from the edge of the table
ethanol = wear eye protection + keep away from naked flame
use forceps to hold tissue being cut
58
dehydrogenase
Dehydrogenase is an enzyme found in plant chloroplasts that is crucial to the light
dependent stage of photosynthesis. In the light dependent stage, electrons are
accepted by NADP. Dehydrogenase catalyses this reaction.
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.
Transfer to centrifuge tubes and centrifuge at high speed for 10 minutes. This will
separate chloroplasts into the pellet.
4. Remove supernatant and add pellet to the fresh isolation medium. Store isolation
solution on ice.
5. Set the colorimeter to the red filter. Zero using a cuvette containing chloroplast extract
and distilled water.
6. Place test tube in the rack 30cm from light source and add DCPIP. Immediately take a
sample and add to cuvette. Measure the absorbance of the sample using the
colorimeter.
7. Take a sample and measure its absorbance every 2 minutes for 10 minutes.
8. Repeat for different distances from lamp up to 100 cm. This will vary the light intensity.
plot graph of absorbance against time
59
conclusion DCPIP practical
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.
60
rate of respiration
1/mean time
61
Respiration practical
1. Set up a water bath at 35°C.
2. Add 5cm3
of the yeast and glucose solution to three test tubes. Place test tubes
in the water bath and leave them, for the solution to equilibrate for 10 minutes.
3. Add 2cm3
of methylene blue to the test tubes and start the timer. Shake for 10
seconds and place test tube back in water bath. Record how long it takes for the
methylene blue to turn colourless for each test tube.
4. Repeat the experiment using temperatures of 40°C, 50°C, 60°C and 70°C.
5. Find the mean of the results for each temperature and use to calculate the
average rate of respiration.
NB: the yeast and glucose solution should be buffered to maintain a constant pH.
62
apparatus to use in serial dilutions
micropipette
63
when using a high power microscope with an objective (oil immersion) which practice is essential to achieve optimal resolution
-using immersion oil
64
electrophoresis separates biological molecules primarily based on
molecular charge
65
aseptic technique for handling agar plate
-regularly opening container lid
66
calculating bacteria/cell culture
2^no generations x initial number of bacteria = total number of bacteria
67
when given scale bar
measure scale bar to get image size not the image shown
68
Calculating uncertainty
-calculate mean
-find the range
-divide the range by 2
e.g mean = 1.26
0.1 = range
0.1 / 2 = 0.05
Uncertainty = 1.26+-0.05
69
calculating percentage uncertainty / error
uncertainty / mean x 100
if given 2 values add the percentages at the end
70
equations for serial dilutions
C1 x V1 = C2 x V2
V2 = V1 + vol of distilled water to dilute with
C1 = conc of stock solution
V1 = volume of stock solution used to make new conc
C2 = conc of solution you are making
V2 = volume of new solution
71
dilution series method
-add 1 part bacteria culture to 9 parts water
-mix thoroughly
-repeat using 9 parts water and 10-1
-repeat using 9 parts water and 1 part 10-2 to make 10-3 dilution
72
how would you produce an extract of chloroplasts
-grind leaf using pestle and motar with a little sand to break down cell walls
-include isolation medium to help break down cell walls further
-filter through layer of muslin to remove cell debris
-dilute in the isolation medium
