paper one practicals

Question 1

experiment to investigate heart rate of daphnia

Answer 1

1. Make up at least five different caffeine solutions of diff concentration and a control solution
2. Transfer one daphnia onto cavity slide
3. Using pipette place five drops onto daphnia. 4. Wait five minutes so it absorbs
4. Place under microscope and adjust focus
5. Count heart beats in twenty seconds
   Repeat ten times using same conc but different daphnia
   7.repeat using other concs
   Controls : temperature, volume of caffeine solution.

Question 2

experiment to investigate vitamin c content

Answer 2

1. Transfer 1cm of ​DCPIP solution​ into a test tube with a pipette.
2. Add ​Vitamin C solution dropwise​ to the DCPIP solution. Shake after each drop.
3. Record the ​volume​ of Vitamin C that is required to ​change the colour​ of the
   DCPIP.
4. Repeat the experiment (to get concordant results) and replace the Vitamin C solution with the ​fruit juices
5. Use a calibration curve to determine vit c content
   REMEMBER IN EXPERIMENTS
   Controls and at least five samples

Question 3

experiment to investigate membrane permeability

Answer 3

1. Cut beetroot into 8 ​identical cylinders​ using a cork borer and wipe/rinse to clean off any pigment​ released as a result.
   Place each of the cylinders of beetroot in 10 ml of distilled water. Place each test tube in a ​water bath​ at a ​range of temperatures ​between​ ​0 and 70​°​C.
2. Leave the samples for ​15​ minutes​- pigment will leak out of the beetroot.
3. Record the exact temperature of the ​water bath ​using the thermometer.
4. Remove the test tubes from the water baths and remove the cylinders of beetroot
   from them. Decant the liquid into clean test tubes.
5. Set the colorimeter to a ​blue filter​ and​ zero​ using a cuvette with ​distilled water​.
6. Filter each sample into a cuvette using ​filter paper
   Measure the ​absorbance​ for each solution. A ​higher absorbance​ indicates higher pigment concentration​, and hence a ​more permeable membrane

Question 4

the effect of changing enzyme concentration on the rate of reaction

Answer 4

1. Dilute stock solution of trypsin with distilled water to produce solutions with
   concentrations of 0.2%, 0.4%, 0.6% and 0.8%.
2. Make a control by adding 2cm3 of trypsin solution and 2cm3 of distilled water.
   Use this to set the colorimeter absorbance to zero.
3. To another cuvette, add 2cm3 of milk suspension and 2cm3 of the stock trypsin
   solution. Mix, place in the colorimeter and measure absorbance at 15 second
   intervals for 5 minutes.
4. Rinse the cuvette with distilled water.
5. Repeat step 3 at all trypsin concentrations.

Question 5

observing stages of mitosis practical

Answer 5

1. Cut a 5mm sample of the root tip using a scalpel.
2. Transfer root tip to sample tubes containing HCl and leave for 5 minutes.
3. Transfer to watch glass containing cold distilled water. Leave for 5 minutes.
4. Dry root tips on filter paper.
5. Place tip on a microscope slide. Macerate with a needle to spread the cells out.
   This makes the chromosomes visible and will therefore show which cells are
   undergoing mitosis.
6. Add a drop of toluidine blue to the slide and leave to stain for 2 minutes.
7. Lower the cover slip down carefully onto the slide. Make sure there are no air
   bubbles in the slide which may distort the image, and that the coverslip doesn’t
   slide sideways which could damage the chromosomes.
8. Wrap in a paper towel and gently ‘squash’ the slide.
9. Place under a microscope and set the objective lens on the lowest
   magnification, then use the coarse adjustment knob to move the lens down to
   just above the slide.
   10.Use the fine adjustment knob to carefully re-adjust the focus until the image is
   clear
10. calculate mitotic index

Question 6

identifying structures in a stem practical

Answer 6

1. Calibrate the eyepiece graticule by placing both on the stage and lining up the
   divisions of the stage micrometer (which have a known length) with the divisions of the eyepiece graticule (for which the length is unknown) to calculate the length of one division of the graticule.
2. Cut transverse sections of the plant stem (on the white tile using a razor, wet to
   reduce friction) as thinly as possible. Select the thinnest sections.
3. Place one section on a microscope slide. Draw a line in wax crayon from top to
   bottom of the slide either side of the specimen to prevent the dye from spreading. Add
   a few drops of concentrated phloroglucinol and lower the cover slip down carefully
   onto the slide. Make sure there are no air bubbles in the slide which may distort the
   image.
4. Place under a microscope and set the objective lens on the lowest magnification, then
   use the coarse adjustment knob to move the lens down to just above the slide.
5. Use the fine adjustment knob to carefully re-adjust the focus until the image is clear
   (can use a higher magnification if needed).
6. Observe and draw the stem.
7. Measure the size of the stem diameter and vascular bundle using the calibrated
   eyepiece graticule.

Question 7

tensile strength of plant fibres practical

Answer 7

1. Use the forceps to separate the fibres.
2. Test the tensile strength of the fibres by using suspended masses to compare

Question 8

antimicrobial properties practical

Answer 8

1. Carry out aseptic techniques
2. Crush 3g of the garlic and mint (separately) with methylated spirit. Shake
   occasionally.
3. Use a sterile pipette to transfer plant extract to paper disc.
4. Leave paper discs to dry for 10 minutes.
5. Use sterile forceps to place the paper disc onto a petri dish.
6. Lightly tape a lid on, invert and incubate at 25°C for 24 hours. DO NOT tape
   around the entire dish as this prevents oxygen entering and so promotes the
   growth of more harmful anaerobic bacteria.
7. Sterilise equipment used to handle bacteria and disinfect work surfaces.
8. Measure the diameter of the inhibition zone (clear circle) for each plant. DO NOT remove lid from agar plate.
9. Work out the area of the inhibition zone

Question 9

hill reaction experiment

Answer 9

1. Remove stalks from leaf samples. Cut into small sections. Grind sample using a
   pestle and mortar and place into a chilled isolation solution.
2. Place several layers of muslin cloth into funnel and wet with isolation medium to
   filter sample into a beaker.
3. Suspend the beaker in an ice water bath to keep sample chilled.
4. Transfer to centrifuge tubes and centrifuge at high speed for 10 minutes. This
   will separate chloroplasts into the pellet.
5. Remove supernatant and add pellet to fresh isolation medium.
6. Store isolation solution on ice.
7. Set the colorimeter to the red filter. Zero using a cuvette containing chloroplast
   extract and distilled water.
8. Place test tube in rack 30cm from light source and add DCPIP. Immediately take
   a sample and add to cuvette.
9. Measure the absorbance of the sample using the colorimeter
   10.Take a sample and measure its absorbance every 2 minutes for 10 minutes.
   11.Repeat for different distances from lamp up to 100 cm. This will vary the light
   intensity.

Question 10

Investigate the effect of temperature on the rate of an
enzyme-catalysed reaction, to include Q10

Answer 10

1. Grind a known mass of peas in distilled water and place in a boiling tube.
2. Add 5cm of hydrogen peroxide solution to the peas.
3. Fit the syringe into a delivery tube and the delivery tube into the boiling tube with
   a bung.
4. Place the boiling tube into a water bath at a known temperature.
5. Time for a set length of time e.g. 5 minutes. Measure the volume of gas produced at regular intervals e.g. 30 seconds.
6. Repeat the experiment at different temperatures.

Question 11

Investigate the effects of temperature on the development of organisms

Answer 11

1. Place 2g of sea salt into a beaker containing 100 cm of dechlorinated water.
   Stir with the stirring rod until the salt completely dissolves.
2. Put some eggs onto a sheet of paper.
3. Wet a piece of graph paper in salt water. Place it face-down onto the sheet of
   paper so it picks up some eggs.
4. Observe the graph paper under a microscope and count out 40 eggs.
5. Remove the rest of the eggs/the paper so there are only 40 eggs there.
6. Place the graph paper upside-down into the beaker and leave for 3 minutes/until
   all eggs have detached into the water.
7. Incubate the beaker at a set temperature (between about 5 and 35 degrees
   Celsius - this mimics the conditions in the wild) for 24 hours.
8. Remove the beaker from the incubator.
9. Shine a bright light on the beaker. Any hatched larvae will swim towards the light and can then be removed with a pipette.
   10.Return the beaker to the incubator and repeatedly remove and count hatched
   larvae.
   11.Repeat all steps at a range of temperatures

Question 12

why might glucose be added in daphnia experiment

Answer 12

• glucose provides a respiratory substrate
• to provide energy for heart contraction

Question 13

explain why daphnia were left for five minutes in the alcohol/caffeine solution before the heart rate was recorded

Answer 13

• time is required for the alcohol/caffeine to be absorbed
• time is required for acclimatisation

Question 14

why is…
- HCl added to the root tip
- a stain added to the root tip
….when investigating mitosis

Answer 14

HCl breaks down middle lamella allowing light to pass through
a stain makes the chromosomes visible so that the stages of mitosis can be identified

Question 15

when investigating microbial properties suggest …
- why the bacteria is mixed with agar
- why the petri dish must be sterile
- why the two halves of the petri dish are not completely sealed with tape
- a suitable temp for safe incubation in a school lab

Answer 15

• so the bacteria are distributed evenly
• prevents contamination of other bacteria, stops bacteria from being cultured
• allows air in, oxygen required for aerobic respiration by the bacteria
• 20-30 degrees. above this bacteria would be encouraged to grow

Question 16

investigating the effect of different antibiotics

Answer 16

1. Carry out the whole experiment using aseptic technique.
2. Flame the forceps and pick up a paper disc.
3. Slightly lift the lid of the petri dish and place the paper disc onto the agar.
4. Tape the dish with two pieces of sellotape (don’t tape all the way around to
   avoid conditions becoming anoxic).
5. Wash your hands and disinfect the bench.
6. Incubate for 24 hours at approximately 30 degrees.
7. Measure the radius of the clear zone on the agar plate. Calculate the area

Question 17

using a transect practical

Answer 17

1. Choose a site where there is an obvious gradient in an abiotic variable. Place the
   transect down. Select a species that changes in abundance along the gradient.
2. Place the quadrat at each of the marks on the transect, placing the bottom left
   corner on the mark every time.
3. Record the percentage cover for the chosen species. This can be done by
   recording how many of the quadrat’s 100 squares contain the chosen species. A
   square should only be counted if half or more of it is covered.
4. At each coordinate, a measure of the independent variable should be taken.
   For example, if investigating light intensity, a photometer can be used to take a
   reading for the light intensity at each coordinate.

Question 18

what must you do when using a quadrat

Answer 18

RANDOM SAMPLING