Required Practicals Flashcards
1
Q
- describe a method to investigate the effect of temperature on the rate of enzyme (trypsin) activity
A
- make a control sample of just milk solution
- add milk solution to 5 test tubes labelled with 20C, 30C, 40C, 50C & 60C
- in separate test tubes at 2cm^3 trypsin solution & 2cm^3 pH7 buffer solution
- put test tubes containing milk solution & trypsin with buffer into a water bath at 20C for 5 mins
- repeat for all temperatures
- add trypsin & buffer solution into the test tube of milk solution, place back into water bath & time for 4 minutes using a stopclock
- after 4 mins, put contents of test tube into a cuvette into a colorimeter & measure absorbance immediately
(alternatively time how long it takes for solution to go colourless) - plot graph of temperature vs absorbance
- the smaller the absorbance, the greater the rate of enzyme activity
2
Q
- describe a method to use an optical microscope to identify the stages of mitosis in root tip squashes & to calculate mitotic index
A
- heat 1 mol of HCl in 60C hot water bath
- cut root sample using a scalpel, place in HCl & leave in hot water bath for 5 minutes
- wash roots in cold distilled water & cut the tips of the roots with a scalpel
- place into acetic orcein stain & leave in water bath for 5 mins
- place stained root tip on slide
- place cover slip on top of root tip & squash them down
- put the prepared slide under the microscope & set objective lens to lowest magnification
- use the coarse & fine adjustment knob to focus the image
- on highest magnification objective lens (X40), count the number of cells in mitosis & the total number of cells
- make a biological drawing
- mitotic index = # cells with visible chromosomes/total # cells
3
Q
- describe a method to identify the water potential of potato tuber cells by a dilution series
A
- make a series of dilutions with distilled water of 1M sucrose (or salt) solution at 0.0M, 0.2M, 0.4M, 0.6M, 0.8M & 1.0M sucrose
- measure 10cm^3 of each dilution into separate test tubes
- use a ruler & scalpel to cut out 6 potato chips of equal dimensions. blot with paper towel to remove excess water (do not squeeze)
- weigh each potato chip using a mass balance
- place 1 potato chip in each test tube & leave for 20 mins
- remove each potato chip, blot dry with paper towel & reweigh them
- calculate the % change in mass for each potato chip
- plot graph of conc vs % change in mass
4
Q
- describe a method to investigate the effect of temperature on the permeability of cell surface membranes (beetroot leakage)
A
- cut beetroot into 10 equal dimension cubes
- label 10 test tubes with relevant temperature (20-80) & put 5cm^3 distilled water in each
- put each test tube in a water bath at the given temperature
- put 5 beetroot cubes into the water bath for 1 minute then put in labelled test tube for 20mins
- after 20mins, pour coloured water into a cuvette & into a colorimeter
- set colorimeter to blue filter, calibrate with distilled water, then measure absorbance
- plot graph of temperature vs absorbance
- higher absorbance = higher pigment conc. = higher membrane permeability
5
Q
what must be done before using a colorimeter?
A
calibrate colorimeter with distilled water
= zero it
6
Q
- describe precautions when dissecting e.g. a mammalian heart & lungs
A
disinfect surfaces
wear gloves
observe outside of heart & lungs before dissection
use scalpel & make sharp, precise cuts
7
Q
6a. describe a method to investigate the effect of antimicrobial substances on microbial growth
A
- use aseptic technique (describe throughout)
- use a sterile pipette & flame neck of bottle to remove some E.coli broth
- lift lid of petri dish facing the Bunsen flame & place a few drops of E.coli on the agar plate
- flame a glass spreader, let it cool, then spread bacteria evenly on surface of agar
- use sterile forceps to place filter paper discs soaked in antimicrobial solution onto the centre of the agar plate
- secure the lid of the petri dish with 2 pieces of tape & put upside down in incubator @ 25C for 48 hrs
- after incubation, measure the diamater & calculate the area of the zone of inhibition for each antibiotic using A=pir^2
8
Q
describe & explain examples of aseptic technique
A
wash hands with soap & disinfect surfaces
use sterile pipette
flame the neck of the bottle, glass spreader & forceps in a (roaring) Bunsen flame
lift the lid of the petri dish towards the Bunsen safety flame, which creates convection current/upwards air movement so microogranisms moved away
discard apparatus in a beaker of disinfectant
9
Q
6b. describe a method to investigate the effects of antimicrobial substances on the growth of bacterial populations in a broth culture
A
- use aseptic technique (describe throughout)
- use a sterile pipette & flame neck of bottle to remove some M. luteus broth & place 1cm^3 in the first bottle of disinfectant
- remove 1cm^2 from first bottle & place in 2nd bottle & repeat for all bottles, removing 1cm^3 from final bottle & discarding it
- for each dilution take 0.1cm^3 with a sterile pipette
- lift lid of petri dish towards Bunsen flame & place dilution solution on agar plate
- flame a glass spreader, let it cool, & spread dilution evenly over the surface of the agar
- secure the lid of the petri dish with 2 pieces of tape & put upside down in incubator @ 25C for 48 hrs
- after incubation, count individual colonies of bacteria, X by dilution factor X 10 to calculate an estimation for # of bacterial cells in original sample per mL
10
Q
- describe a method to investigate the effect of temperature on the rate of respiration of cultures of single-celled organisms
A
- set up a water bath at 35C
- add 5cm3 of the yeast & glucose solution to a test tube & leave it until the contents reach 35C
- add 2cm3 methylene blue to each test tube & start the timer. shake the tube for 10 seconds then put back into water bath
- record how long it takes for the methylene blue to turn colourless for each test tube
- repeat the experiment at 25C, 40C, 45C & 55C, 60C
- find the mean mean time for each temperature & use it to calculate the average rate of respiration: rate = 1/time
- plot a graph of temperature against rate of respiration
11
Q
- describe a method to investigate the effect of an environmental variable on the movement of an animal using a choice chamber
A
- set up choice chamber with 4 quadrants: dark & dry, dark & damp, light & dry, light & damp
- use dark paper to block light on one half & wet paper towel to make damp areas. use anhydrous calcium chloride to make dry areas.
- place 10 woodlice in centre of choice chamber & leave them for 10 mins
- after 10 mins, record how many woodlice are in each quadrant
- repeat by moving woodlice back into centre of choice chamber
12
Q
- describe a method to investigate the effect of an environmental variable on the movement of an animal using a maze (did in class)
A
- place a maggot at the start of the maze
- record whether the maggot turnes left or right when it reaches a junction
- remove the maggot & wipe to inside of the maze with cotton wool
- repeat for 20 maggots
- to test for turn alteration, place a maggot at point before a right turn
- record whether the maggot turns left or right after turning right
- repeat for 20 maggots, using a new maggot each time & wiping the maze in b/w tests
thigmotaxis
13
Q
how are the results of the maggot/woodlice experiment analysed?
A
Chi squared test - determines whether the observes result differ from the expected results
X2 = ∑(o-e)^2 / e
if the value exceeds the critical value at the 0.05 significance level, reject H0 –> statistically significant
14
Q
why must a new maggot be used each time?
A
to avoid the maggot learning which way to turn
15
Q
why is the maze wiped down each time?
A
to prevent chemotaxis - following the trail of the previous maggot
16
Q
describe a method to produce a calibration curve using a colorimeter
A
use distilled water & the sample to create a dilution series
use a known volume of solution
measure absorbance/transmission of the solutions using a colorimeter
plot graph of concentration of solution against absorbance/transmission
17
Q
- describe a method to produce a dilution series of a glucose solution & use colorimetric techniques to make a calibration curve to identify concentration of unknown ‘urine’ sample
A
- create a dilution series of glucose solutions using distilled water of conc. 1-10mmoldm-3
- place 2cm3 of each unknown sample into separate boiling tubes & 2cm3 benedict’s solution to each
- put boiling tubes in water bath & heat
- measure the absorbance of each known sample using the colorimeter
- plot graph of the known concentration of solution against absorbance/transmission = calibration curve
- measure the absorbance of the unknown samples using the colorimeter & read off the concentration from the calibration curve
18
Q
- describe a method to investigate the effect of a named environmental factor on the distribution of a given species
A
- use 2 tape measures to split the study area into a grid with coordinates
- use a random number generator to randomly select a set of coordinates
- place the (bottom left of) 0.25m2 quadrat at the coordinates & count the # of individuals in the quadrat (or % cover by counting how many of the 100 squares in quadrat contain the given species)
- repeat at least 20 times
- calculate a mean, find area of field & multiply together to estimate population size
NB if investigating light intensity, use photometer can be take a reading for light intensity
19
Q
/mm2 using a microscope
A
