Practicals

Question 1

measurement error

Answer 1

th difference between a measured value and the true value

Question 2

anomaly

Answer 2

values in a set of results which are judged not to be part of the variation caused by random uncertainty

Question 3

random error

Answer 3

cause readings to be spread about the true value due to results varying in an unpredictable way
they can be reduced by making more measurements and calculating a mean

Question 4

systematic error

Answer 4

causes readings to differ by a consistent amount each time
can be due to environment or instruments be used
data collection should be repeated using a different technique or equipment

Question 5

zero error

Answer 5

a false reading when the true value of a measured quantity is zero
can result in systematic uncertainty

Question 6

precision

Answer 6

very little spread around the mean value
depends on the extent of random erros

Question 7

repeatable

Answer 7

the original experimenter repeats the investigation using the same method and equipment and obtains the same results

Question 8

reproducible

Answer 8

investigation is repeated by another person or by using different equipment or techniques and the same results are obtained

Question 9

uncertainty

Answer 9

interval within the true value can be expected to lie, with a given level of confidence or probability

Question 10

accuracy

Answer 10

how close a blue is to the true value

Question 11

reading

Answer 11

the values found from a single judgement when using a piece of equipment
±0.5 of the smallest scale reading

Question 12

measurement

Answer 12

the values taken as the difference between the judgements of two values
±1 of the smallest scale reading

Question 13

% uncertainty

Answer 13

uncertainty/value x 100

Question 14

% uncertainty in a repeated measurement

Answer 14

uncertainty/mean value x 100

Question 15

when to use correlation coefficient

Answer 15

if you are looking for association between data

Question 16

when to use chi-squared test

Answer 16

when comparing frequencies

Question 17

when to use student’s t-test or

Answer 17

comparing two means

Question 18

layout of a response to an evaluation/conclusion of an investigation

Answer 18

formulate/evaluate the null hypothesisselect and justify a statistical testinterpret a given probability that the difference of results is due to chance (if p

Question 19

describe rp 1a: effect of a factor on the rate of an enzyme controlled reaction

Answer 19

vary the conc of substrate hydrogen peroxide - see the effect on the rate of a reaction catalysed by enzyme catalase (hydrolyses hydrogen peroxide into water and oxygen)set up a boiling tube with hydrogen peroxide, yeast, and a pH 7 buffer and put it in a water bathshake the yeast suspension before each sample is takenhave a stopper with a delivery tube that leads to an inverted burette in a large beaker of water read and record the burette reading mix the reaction mixtures bubbles of air will displace water in the burette downwards after 60s, note the position of the meniscus, record and calculate the volume of oxygen produced repeat with different concentrations of hydrogen peroxide

Question 20

describe rp 1b: investigation on the effect of temperature on trypsin

Answer 20

make two control samples: one that has the milk suspension and distilled water (to indicate the absence of enzyme activity) and one with the milk suspension and hydrochloric acid (to indicate the colour of a completely hydrolysed sample)take three test tubes and measure 5cm3 milk into each - place in a water bath at 10°C for 5 mins to equilibrate add 5cm3 trypsin to each test tube simultaneously and start the timer record how long it takes for the milk samples to completely hydrolyse and become colourless (this can be tested by marking a dot on one side of the glass and waiting for this to become visible)repeat at different temperaturesfind the mean time for the milk to be hydrolysed at each temperature

Question 21

describe rp 2: root tip squash

Answer 21

fill a vial with 1M HCl and place it into a beaker of hot wateradd a section of garlic clove with roots into the acid and leave for 5 minutesremove the garlic from the acid and rinse it in the beaker of hot watertransfer the clove to a tile and cut the last 1-2mm of the root tip off using a scalpeluse forceps to transfer the tip to a slide and tease the root apart with 2 mounted needles to separate the cells into a singular layeradd a drop of toluidine blue and place a cover slip, cover with a paper towel and press firmly to squash and spread the cells place under a microscope and observe

Question 22

describe rp 3: osmosis - identifying the water potential of a plant tissue

Answer 22

label six boiling tubes 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 mol dm-3 sucroseuse 1.0 mol dm-3 sucrose solution and distilled water to make up 20cm3 of each of the above concentrations stand the boiling tubes in a water bath at 30°Cusing an apple corer, cut six equal size potato chips and blot but don’t squeezeweigh each potato chip and record these initial masses transfer each potato chip to its corresponding boiling tube and start a timerafter 20 mins remove and blot then reweigh and recordplot a graph of % change in mass against concentration of solution, where the line crosses the x axis (no change in mass), this is the water potential of the tissue

Question 23

describe rp 4: investigating cell membrane permeability

Answer 23

use beetroot extract and water to prepare 6 solutions different concentrations, which increase at regular intervals from 0% to 100%set up a colorimeter, use distilled water to calibrate and then measure and record the absorbance of each of the standards preparedadd 2cm3 of 100% alcohol to a test tube and put a bung in the tube - label it with the alcohol concrepeat this with alc conc of 80, 60, 40, and 20%collect 10 discs of beetroot of equal size then blot and put the discs into a boiling tube of distilled waterput a bung in this boiling tube and shake - repeat this until the water is free of pigmentput two discs of beetroot into each of the alcohol tubes and leave for 5 minutesremove beetroot and measure and record the absorbance of each of the solutions - use a calibration curve to determine the conc

Question 24

describe tdp: investigating transpiration with a potometer

Answer 24

cut a shoot around 30cm long and put the cut end in waterprepare a potometer by completely filling the syringe, capillary tube, and rubber tubing with water, making sure there’s no air bubblecut another 2cm still underwater off the end and attach the rubber tube of the potometer - clamp it so the capillary tube is horizontal turn the valve so the shoot can obtain water from the capillary tube record the initial position of the meniscus on the capillary tube and start a timer for 1 minute - record how far the meniscus moves in this time refill the tube and repeat - can investigate factors like temp or light intesnsity

Question 25

describe rp 6: microbiology

Answer 25

wipe down area with disinfectant wipes and place sterile plastic sheet on the benchplace bunsen burner on a heat proof mat and light write name, date, and type of bacteria on underside of petri dish wash handsremove molten agar from water bath place petri dish, bacterial culture, and molten agar bottle near roaring flame open test tube with bacteria and flame neck of bottledip in sterile pipette and remove some of the bacteria - flame the neck again and replace the lidremove lid of molten agar and flame neck, add bacteria to the bottle, flame neck and replace lid discard pipette into disinfectant gently invert molten agar 5 times, remove lid and flame neck, lift lid of petri dish at angle to face the flame and pour in contents of the bottleplace empty bottle in disinfectantreplace the lid of the agar plate and swirl contents then leave to set dip forceps in ethanol then flame, use them to place multodisk on centre of agar plate resterilise forceps hold lid of plate with two pieces of tape and leave it to incubate upside down at 25oCobserve which colonies were able to grow and measure zones of inhibition using πr2

Question 26

descrive rp 7: use chromatography to isolate pigments from leaves of different plants

Answer 26

take a piece of TLC paper and rule a pencil line 2cm3 from the bottomscrape/blend leaves to extract green liquid using a small dropping pipette, place one drop of solvent onto the extracted liquid and mix use a clean pipette to transfer the liquid onto a watch glassuse a hairdryer to gently evaporate the solvent again add a drop of solvent and mixdip the end of a capillary tube into the liquid then transfer to a spot in the middle of the pencil line on the TLC paper, allow this to dry and repeat x3 on the same spotplace the paper upright in a boiling tube with solvent and a bung remove when the solvent has moved to 1cm from the top and note the final position of the solventcalculate rf values for each pigment and use it to identify them

Question 27

describe rp 8: dehydrogenase activity in extracts of chloroplasts

Answer 27

attach a 5cm length of double sided sticky tape across the middle of white cardlabel 4 small watch glasses ABC and Duse a pipette to transfer 2 drops of chloroplast extract to A, B and Duse a pipette to add 1 drop DCPIP to A, B and C and mixuse capillary tubes to draw up mixtures from ABC and D place them onto the tape and place black paper over half the capillary tubeshine light directly onto the tubes and leave for ten minutesit should show that in lower light intensity DCPIP takes longer to turn colourless

Question 28

describe rp 9: factors affecting rate of respiration

Answer 28

fill a syringe with 10cm3 yeast suspension followed by 10cm3 glucose solution orientate the syringe vertically and draw up a small amount of airplace a finger over the top of the syringe and mix the contentsempty out the air attach the capillary tube to the syringe place the end of the capillary tube into a beaker of water and slowly move the syringe plunger out, allowing water to enter the tube then remove the capillary tube from the water but dontinue to withdraw the plunger so some air enters, continue until the air/water interface is near the syringe wait for 2 mins so pressure can equalisemeasure the time it takes for the meniscuc to travel a set distance and record the resultsrepeat with other sugar solutions

Question 29

describe rp 10a: investigating animal responses uses a choice chamber

Answer 29

set up the choice chamber with nothing in the base quarters place 12 woodlice in the chamber through the hole using a brush wait 4 minutes then record the no. woodlice in each half of the chamber (expected results should be 6 in each half or other but with a stat test outcome of a p value over 0.05)cover half the choice chamber with black paper to make it dark place damp paper towels in two quarters (one light one dark) and do the same with drying agentleave the woodlice for 4 minutes and record the distribution in each quarter

Question 30

describe rp 10b: investigating animal responses in a maze

Answer 30

set up a maze where an animal comes to a T and has the option to turn left or right - record how many turn left and how many turn rightthen set up a bend in the maze so the animal is forced to turn left before reaching the T - then record how many turn left vs right at the Tthis tests the hypothesis of turn alteration behaviour - when forced to turn in one direction, an animal will subsequently choose to turn in the opposite direction

Question 31

describe rp 11: investigating glucose concentration in urine

Answer 31

create a dilution series of glucose using distilled waterplace 2cm3 of each of the unknown samples in separate boiling tubesadd 2cm3 benedict's solution to all boiling tubesplace them in a water bath at 90°C for four minutescalibrate the colorimeter using distilled water place the known samples into cuvettes and measure and record the absorbances make a calibration curve of absorbance against glucose concentrationplace the unknown samples into the cuvettes and measure and record their absorbancesuse the calibration curve to find their concentrations

Question 32

describe rp 12: investigating inheritance patterns in drosophila

Answer 32

transfer 5 pure breeding virgin females and 5 pure breeding vestigial wing males into a new bottle containing culture medium incubate at 25°C for 7 daysremove the parent flies and incubate for another 7 days to allow the F1 generation to develop into adultsanaesthetise all the F1 generation and count the number of flies in categories female normal, female vestigial, male normal, male vestigialcross the F1 generation by transferring 5 males and 5 females into a new culture bottle incubate for 7 days and remove parentsincubate for another 7 days to allow the F2 generation to develop into adults anaesthetise the F2 generation and count the number of flies in categories female normal, female vestigial, male normal, male vestigial