Biology practicals

How can you measure the effect of caffeine on heart rate

1. Prepare 5 different concentrations of caffeine solution and a control of distilled water

2. Add pond water to a cavity slide and add 3 drops of distilled water

3. Select a large daphnia and transfer it to the cavity slide using a pipette

4. Place the cavity slide onto the stage and observe it under a low power

5. Using a stopwatch, time for 20 seconds and count the number of heart beats

6. Multiply your answer by 3 to get the number of beats per minute

7. Return the daphnia

8. Repeat this with at least 5 other daphnia individuals

9. Repeat the entire experiment for the different caffeine concentrations

Why are there more ethical concerns to using a vertibrate to an invertibrate in experiments

vertibrates are more likely to feel pain

Why are daphnia used to measure heart rate

They are transparent, so their internal organs can be viewed under a light microscope and caffeine can diffuse through their skin

Method for counting heart beats of daphnia

Use a piece of paper and pen and make a dot every time you see a beat

Ethical considerations when using daphnia for research

- They deserve respect as they cannot consent and cannot express pain

- Animals should be handled gently, examinations should be kept short and should be returned immediately to their tank once examined

- Extreme variables should be avoided e.g. extreme temperatures

Vitamin C

Found in green vegetables, fruit and potatoes.

Known as ascorbic acid

Good reducing agent and easily oxidised

How to investigate vitamin C content

1. Make up 6 known vitamin C concentrations

2. Measure out 1cm^3 of DCPIP solution into a test tube, using a measuring cylinder

3. Add one of the vitamin C concentrations to the DCPIP solution, drop by drop, using a pipette or biurette, shaking the tube for a set period of time after each drop

4. When the solution turns from blue to colourless, record the volume of vitamin C added

5. Repeat steps 2-4 for the same concentration twice more

6. Repeat steps 2-5 for the rest of the concentrations

7. Create a calibration curve by plotting a line of best fit, showing vitamin C volume used against concentration

8. Repeat steps 2-5 with fruit juices of unknown concentrations, using the calibration curve to find the concentration

Name a control used during the vitamin C experiment

The time the test tube is shaken after each drop of solution added

Risks for vitamin C experiment

DCPIP is an irritant, so safety goggles should be used

How to calculate the mass of vitamin C used in the experiment

Mass of vitamin C to decolourise 1cm³ of DCPIP = 10 mg × volume of vitamin C used

Mass of vitamin C in fruit juice sample = mass of vitamin C to decolourise 1cm³ of DCPIP × volume of fruit juice used

How to measure the effect of enzyme concentration on the rate of reaction

1. Add a set volume of hydrogen peroxide solution to a boiling tube

2. Add a set volume of buffer solution to the same tube

3. Invert a full cylinder in a trough of water

4. Place the end of a delivery tube into the open end of the measuring cylinder and attach the other end to a bung

5. Add a set concentration of one concentration of catalase to the boiling tube and quickly attach the bung

6. Record the volume of oxygen collected in the measuring cylinder every 10 seconds for 60 seconds

7. Repeat steps 1-6 for the same concentration twice more and calculate a mean

8. Repeat the whole experiment with different concentrations of catalase

How to measure the effect of substrate concentration on rate of reaction

Use a range of substrate concentrations

Add iodine to starch, creating a blue-black solution

Add amylase, which will begin to break down the starch into glucose, and use a colorimeter to measure the absorbance every 10 seconds until it turns colourless

Repeat this for a range of starch concentrations

How to measure the effect of temperature on membrane permeability

1. Using a cork borer and scalpel, cut five equal-sized sections of beetroot

2. Rinse the beetroot pieces

3. Add the beetroot pieces to five different test tubes, each containing the same volume of water, e.g. 5 cm3

4. Put each test tube in a water bath at a different temperature, e.g. 10 ℃, 20 ℃, 30 ℃, 40 ℃, and 50 ℃, for the same length of time

5. Remove the beetroot pieces, leaving just the coloured liquid in the five test tubes

6. Use pipettes to transfer samples of the coloured liquid to colorimeter cuvettes

7. Use a colorimeter to measure how much light is absorbed as it passes through each of the five samples of coloured liquid

8. The higher the absorbance, the more pigment must have been released due to a greater membrane permeability

How to view plant stems under a microscope

- Calibrate the eyepiece graticule

- Cut transverse sections of the plant stem, using a scalpel on a white tile, as thinly as possible and select the thinnest pieces

- Place a sample onto a slide and use a wax crayon to draw a line either side to prevent the dye from spreading

- Add a few drops of concentrated phloroglucanol and lower the coverslip carefully avoiding airbubbles

- Place under a microscope on the lowest objective lense magnification and use the coarse adjustment knob to lower the lense to just above the slide

- Use the fine adjustment knob to adjust the focus

How to calibrate the eyepiece graticule

- Place both on the stage and line up the divisions of the stage micrometer, with known length, with the divisions of the eyepiece graticule, with unknown length. This can be used to calculate the length of one division of the graticule.

How to test nutrient deficiencies in plants

- Use a measuring cylinder to fill the test tubes with the nutrient solutions: All minerals, no nitrogen, no magnesium, no calcium and no nutrients

- Cover the top of each one with tinfoil and poke a hole

- Push a plantlet through each hole into the solution

- Wrap the tubes in tinfoil and leave by a sunny window

Why is it more ethical to use invertebrates in testing

They are less likely to feel pain

Transmission electron microscope

- use electromagnets to focus a beam of electrons through a specimen

- Denser parts absorb more electrons so are darker

- Give high resolution images but can only be used on thin specimens

Scanning electron microscope

- Knock electrons off the specimen, which are collected in a cathode ray tube to form an image

- show a 3D image and can be used on thicker specimens, but don't give high resolution