Required Practicals Flashcards
Outline a method to produce a serial dilution
- Add 10ml of the stock solution to a test tube
- Transfer 1ml to the next test tube.
- Add 9ml of water to this test tube and mix.
- Transfer 1ml of the second solution to the third test tube.
- Add 9ml of water to this test tube and mix.
- Repeat until all concentrations are prepared.
What is a serial dilution used for?
-solutions with very small concentrations can be made without having to measure out small volumes
-increases accuracy
Formula for serial dilution calculations
C1V1 = C2V2
What is a potometer?
-apparatus that indirectly measures rate of transpiration by measuring rate of water uptake as a result of water loss from plant
-as transpiration occurs from leaves, plant pulls up more water from potometer by cohesion-tension
-causes the bubble to move towards the plant
-the more water lost by transpiration, the more water taken up, the further the bubble moves
-rate of transpiration = volume of transpiration divided by time
-volume of transpiration = distance bubble moved x cross-sectional area of tube (πr2)
Describe a method to measure the rate of transpiration.
Method:
-choose healthy leaf and shoot
-cut shoot underwater and connect to potometer underwater (prevents air bubbles entering = blocks xylem = breaks continuous column of water)
-fill the potometer with water (done underwater to remove all air bubbles)
-cut section is attached to potometer using rubber seals and petroleum jelly (makes equipment air tight = no air bubbles enter = no disruption in flow of water)
-also prevents water from leaking out (lowers accuracy of measurement of water uptake)
-one air bubble is introduced through capillary tube which is lifted out of water
-restore capillary tube back in water
-measure the distance that the air bubble has moved towards the plant and the time it has taken
Why is it difficult to measure transpiration?
What is measured instead and why?
-water is in the form of vapour
-water uptake can indicate the rate of transpiration, as water uptake is almost proportional to transpiration
How can sunlight be replicated when doing experiments with plants?
Lamp
How can wind be replicated when doing experiments with plants?
Fan
How can humidity be increased when doing experiments with plants?
Plastic bag over the plant
When using a potometer to measure the rate of water uptake, why must the apparatus be set up and the plant shoot be cut underwater?
-cohesion-tension creates a negative pressure in the xylem
-cutting it in air would draw air into the xylem
-breaks continuous water column
-prevents or slows down transpiration
-lowers accuracy of measurement of water uprake
-cutting underwater means only water enters the xylem
When using a potometer to measure the rate of water uptake, why must all the joints in the apparatus be covered in petroleum jelly?
-petroleum jelly is waterproof
-prevents any water leaking out
-ensures water can only leave by evaporating out of the stomata
What variables could be controlled when experimenting on two different plant species?
-surface area of leaves (number and size of leaves)
Checklist for a good biological drawing?
-title
-scale or magnification indicator
-sharp pencil
-no shading/colouring
-proportions and size of observable structures must be accurate
-label structures using lines that do not overlap
-continuous line drawing
What should you do to the eyepiece graticule when changing objective lens and why?
-calibrate it using a stage micrometer (each division is usually 10 micrometres)
-magnification changes
Outline a method to calibrate an eyepiece graticule using a stage micrometer
- Line up the stage micrometer and eyepiece graticule while looking through the eyepiece
- Count number of divisions on eyepiece graticule that fit into one division on the micrometer scale
- Divide the length of each division on the micrometer by this number
All food tests
Starch:
-add iodine solution
-positive result: orange/brown to blue/black
Reducing sugar:
-add Benedict’s reagent and heat
-positive result: blue solution to green/yellow/orange/brick-red precipitate
Non-reducing sugar:
-add HCl and boil
-cool the solution
-add sodium hydrogencarbonate to neutralise
-add Benedict’s reagent and heat
-positive result: blue solution to green/yellow/orange/brick-red precipitate
Protein:
-add Biuret reagent
-positive result: blue solution to violet solution
Lipid:
-crush if it is not a liquid
-add ethanol
-add distilled water
-positive result: milky white emulsion forms
How does the non-reducing sugar test work?
-boiling with acid breaks the glycosidic bond
-reducing group becomes exposed
-reduces CuSO4 to CuO
When is chi-squared used?
investigating a whether there is a significant difference in the observed and expected frequencies of an event
When is a student T-test used?
investigating a difference between 2 means
When is the correlation co-efficient used?
investigating an association between 2 measurements
what are the 2 types of data that can be collected?
continuous data: taking measurements
frequency: counting how many individuals are in a category
chi-squared table
What is aseptic technique?
-working in sterile conditions to prevent contamination of other microorganisms on plate
-also prevents infection of others
3 steps of aseptic technique?
Pre-inoculation
Inoculation
Post-inoculation
Pre-inoculation and post-inoculation
-sterilise all equipment and work surfaces with disinfectant to kill microbes
-wash hands with soap to remove microbes
-flame neck of bottle
-flame inoculating loop before use
Inoculation:
-work near a Bunsen burner, or upward convection current (sterilises air)
-open the Petri dish lid at an angle
What should a Petri dish be labelled with?
Initials
Date
Type of bacteria
Method for aseptic technique
-transfer bacteria from broth to agar plate
-use a sterile plastic spreader to evenly distribute bacteria on the plate
-place a multi-disc antibiotic ring on the plate with sterile forceps
-place a lid on top and tape it lightly (ensures O2 can still enter, prevents anaerobic bacteria growing)
-invert plate to prevent condensation dripping down onto agar
-incubate it at 25 degrees C for 48 hours (high temp = harmful bacteria could grow)
-after incubation, for each antibiotic, measure the diameter of the inhibition zone
-calculate area of inhibition zone
Evaluations for aseptic technique
-only tested a few antibiotics
-need more repeats to identify anomalies
-only tested on one type of bacteria
-side effects of antibiotic on humans is unknown
What does the zone of inhibition look like
What does it show
Clear circle
Bacteria has not grown in that region, hence the antibiotic is effective against it
How to interpret Petri dish after incubation and aseptic technique
Large inhibition zone = more bacteria killed = antibiotic works well
Small/no inhibition zone = bacteria resistant to antibiotic
Design a method to investigate the effect of temperature on the rate of an enzyme-controlled reaction
-draw an X on two test tubes (experimental and control)
-add 10cm3 of 3% milk powder solution to each test tube using a measuring cylinder
-add 4cm3 of pH 7 buffer to a third test tube
-to another test tube, add 2cm3 of pH 7 buffer + 2cm3 trypsin solution
-heat all 4 tubes to 20 degrees C for 5 minutes using a water bath
-they must all be at the same temperature so results are valid
-add trypsin and buffer solution to experimental tube
-add buffer solution to control thbe
-immediately start a timer
-stop when the X becomes visible again and record the time
-repeat at different temperatures
Formula for rate of reaction
1/time
Why are logs used
Practical procedure to investigate mitosis
-cut a 1cm piece of root tip of garlic (actively dividing, as it is most likely to be damaged by environment)
-place in 1M HCl for 5 mins at 55 degrees C (increases rate of reaction)
-rinse root on watch glass in tap water to remove excess acid
-stain with toluidine blue - makes chromosomes visible
-macerate (squash) with needle, so cells are more easily visible
-place tip on microscope slide
-lower glass slip using a mounted needle at 45 degrees to prevent air bubbles
-squash by pressing down (not sideways as chromosomes break = stages of mitosis can’t be identified)
-place under a microscope + set objective lens to lowest magnification
-observe the stages of mitosis
Mitotic index
Number of cell undergoing mitosis
———————————————— X 100
Total number of cells
Interphase is not included, as chromosomes are not visible
Why is hydrochloric acid used in the mitosis practical
Softens and loosens the root tissues
Why is a mounted needle used in the mitosis practical
To lower the cover slip and prevent air bubbles under it
Affects ability to view the slide
Formula to work out number of bacteria from colonies
Number of colonies x dilution factor
—————————————————
Volume of culture plate
What does a normal distribution curve look like?
bell-shaped curve
IAA steps
-proudced in tip
-diffuses to shaded side
-cell elongation occurs in shoots, inhibits growth in roots
