CPACS

Question 1

CPAC 1 - Daphnia heart rate

Answer 1

1. Dilute the caffeine solution with ​distilled water ​to produce several ​different concentrations​.
2. Place some cotton wool (to ​restrict movement​) on a cavity slide. Add ​one​ large water flea.
3. Use filter paper to absorb the water around the flea.
4. Then use a dropping pipette to add a ​few drops of distilled water​ to the slide.
5. Use a stopwatch to time a ​minute ​and record the ​number of heartbeats​.
6. Repeat the experiment, replacing the distilled water with a ​caffeine solution​.

Question 2

CPAC 2 - Investigate the vitamin C content of food and drink.

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 and replace the Vitamin C solution with the ​fruit juices​.

Question 3

CPAC 3 - Investigate membrane structure, including the effect of alcohol concentration or temperature on membrane permeability.

Answer 3

1. Cut beetroot into 8 ​identical cylinders​ using a cork borer
2. Place each of the cylinders of beetroot in 10 ml of distilled water.
3. Place each test tube in a ​water bath​ at a ​range of temperatures ​between​ ​0 and 70​°​C (record with thermometer).
4. Leave the samples for ​15​ minutes (using stopwatch)
5. Remove the test tubes from the water baths and decant the liquid into clean test tubes.
6. Set the colorimeter to a ​blue filter​
7. Measure the ​absorbance​ for each solution. A ​higher absorbance​ indicates higher pigment concentration​, and hence a ​more permeable membrane​.

Question 4

CPAC 5 - Prepare and stain a root tip squash to observe the stages of mitosis.

Answer 4

1. C​ut 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. Leave for five minutes in cold distilled water.
4. Place tip on a microscope slide. ​
5. Add a drop of ​toluidine blue​ and leave to stain for ​2 minutes​.
6. Place cover slip over it
7. Look under microscope
   9.To calculate ​mitotic index​, ​cells ​undergoing mitosis​ must be counted (cells with ​chromosomes visible​), as well as the​ total number of cells​.

Question 5

CPAC 7 - Investigate plant mineral deficiencies.

Answer 5

1. Use the measuring cylinder to fill test tubes with ​each of the nutrient solutions​.
2. Cover the top of the test tube with ​tinfoil​. Poke a hole through the tinfoil.
3. Push the ​roots of the ​Bryophyllum​ plantlets​ through the hole in the tinfoil into
   the solution.
4. Wrap the test tubes in tinfoil (to prevent light getting in) and place them under a
   sunny window​.

Question 6

CPAC 7 - conclusion

Answer 6

● Magnesium​ deficiency: ​stunted growth, yellowed leaves​ (because chlorophyll cannot be synthesised).
● Nitrate​ deficiency: ​yellowed leaves​ with ​red-brown​ cast (because chlorophyll cannot be synthesised as protein synthesis is restricted).
● Calcium​ deficiency: ​stunted growth, weakened stem​ (because the support from the cell wall is reduced and metabolism is restricted due to decreased membrane ​permeability​).

Question 7

CPAC 9 - Antimicrobial properties of plants

Answer 7

1. Carry out ​aseptic techniques​ detailed above.
2. Crush 3g​ of the garlic and mint (separately) with methylated spirit.
3. Leave paper discs to dry for ​10 minutes.
4. place the paper disc onto a ​petri dish​.
5. Lightly tape a lid on, ​invert​ and ​incubate​ at 25°C for 24 hours.
6. Sterilise equipment​ used to handle bacteria and​ disinfect work surfaces.
7. Measure the ​diameter​ of the ​inhibition zone​ (clear circle) for each plant.
8. Work out the ​area​ of the inhibition zone
   NB: Bacteria sample is incubated at ​25°C​ as incubating at 37°C (human body temperature) could enable pathogens to grow that are ​harmful to humans​.

Question 8

CPAC 11 - Investigate photosynthesis using isolated chloroplasts (the Hill reaction).

Answer 8

1. Grind sample using a pestle and mortar and place into a ​chilled isolation solution​.
2. Centrifuge
3. Remove liquid and leave the pellets at the bottom
4. Re-suspend the pellets in chilled isolation solution
5. Set the colorimeter to the ​red filter​.
6. set at a distance from bench lamp
7. Combine chloroplast extract with DCPIP
8. Record absorbance
9. Repeat every 2 minutes
10. Try different distances from lamp

Question 9

CPAC 12 - Investigate the effect of temperature on the rate of an enzyme-catalysed reaction, to include Q1​0.

Answer 9

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 10

CPAC 13 - Investigate the effects of temperature on the development of organisms (such as seedling growth rate, brine shrimp hatch rates).

Answer 10

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.
   Nb: treat the shrimps, eggs and larvae responsibly and ​ethically​ for the duration of the
   experiment and release them into salt water when it is completed.

Question 11

CPAC 15 - Investigate the effect of different antibiotics on bacteria.

Answer 11

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 12

CPAC 15 - conclusion

Answer 12

● The area of the ​zone of inhibition​/ ‘clear zone’ will be more effective when the antibiotics are more effective against the type of bacteria being used.
● How effective an antibiotic is against a certain type of bacteria is dependent on whether the bacteria are ​gram-positive or gram-negative​ and what ​type of antibiotics ​are used.

Question 13

CPAC 16 - Investigate rate of respiration practically.

Answer 13

1. Assemble the respirometer.
2. Add 5g of one organism to the boiling tube and replace the bung.
3. Place a drop of ​coloured manometer fluid​ in the open end of the respirometer.
4. Use a ​syringe​ to draw the fluid as far from the respirometer as possible and record its
   starting position.
5. Close the tap​. Start the stop clock.
6. After five minutes, open the tap. ​Record the end position​ of the coloured liquid.
7. Repeat the process for the other organism.

Question 14

CPAC 16 - conclusion

Answer 14

● Soda lime absorbs carbon dioxide​ that is given out during respiration, so any changes in volume are assumed to be only due to differences in ​oxygen uptake.
● Gas exchange due to ​photosynthesis​ is ignored and all of the gas is assumed to be oxygen.
● Different organisms have different rates of respiration - the ​animals have a higher rate of respiration​ per gram than the plants, as they have a ​higher metabolic rate and require much more energy to be released for movement/reproduction/etc.

Question 15

CPAC 17 - Investigate the effects of exercise on tidal volume, breathing rate, respiratory minute ventilation and oxygen consumption
using data from spirometer traces.

Answer 15

1. Find the ​vertical scale​ by emptying the chamber, starting the kymograph and then forcing a known volume of air into the chamber. This measures the volume of gas in the chamber, and by reading the trace, the movement of the pen on the kymograph​ can be calibrated to the actual volume of air.
2. Find the ​horizontal scale​ by setting it to 1 mm per second, using the switch (or as close to 1 mm per second as possible). This is the speed at which the ​drum turns.
3. A trained member of staff can fill the spirometer with ​medical grade oxygen​.
4. Disinfect the mouthpiece​ and attach it to the tube. Turn the tap so the tube is
   not attached to the spirometer..
5. Subject attaches the nose clip and breathes into the tube for a while to practice.
   When they are comfortable, start the datalogger/kymograph and turn the tap to
   attach the tube to the spirometer.
6. Subject takes ​one forced deep breath​ and then ​breathes normally​ into the
   spirometer for a duration of ​5 minutes maximum​.

Question 16

CPAC 17 - conclusion

Answer 16

● ●
From the calibration of the kymograph, volume of air can be linked to the movement (e.g. in number of squares) of the pen on the kymograph. Therefore, distance can be linked to volume​.
Interpreting the spirometer trace:
○ The ​tidal volume​ is the ​distance from peak to trough​, when the subject is breathing normally.
○ The ​vital capacity​ is the ​distance from peak to trough,​ when the subject takes a forced deep breath.
○ Breathing rate​ is the number of ​peaks in a time corresponding to a minute​ (e.g. total peaks divided by 5).
○ Respiratory minute ventilation​ is calculated by ​multiplying breathing rate by tidal volume​.

If the experiment is repeated after exercise (although not during exercise, because a spirometer can create resistance to breathing and therefore isn’t safe for use during exercise):
○ Tidal volume increases.
○ Vital capacity remains the same (although can be impacted long-term by
regular aerobic exercise).
○ Breathing rate increases.
○ Respiratory minute ventilation increases.

● This is because ​respiration increases during exercise​ because of increased muscle contraction​. Therefore, ​more oxygen is required​ and ​more carbon dioxide is produced​, so breathing rate, tidal volume and therefore respiratory minute ventilation increases to cope with this demand up to the ​maximum aerobic rate​. After this point, minute ventilation will ​plateau to a maximum​ and further respiration will be anaerobic.
NB: ​informed consent​ should be obtained before anyone uses the spirometer, as they are a participant in scientific research. Anyone should be allowed to refrain from participating or contributing their data, and can stop at any time during the practical.

Question 17

CPAC 18 - Investigate habituation to a stimulus.

Answer 17

1. Dampen​ the cotton wool bud in distilled water.
2. Touch the snail between the eye buds with the cotton wool bud
3. Time the ​length of time it takes for the snail to emerge fully​ from its shell
   again.
4. Repeat for a total of ​ten touches