Paper 1

What is the practical for using a light micrscope?

• Prepare a microscope slide. Stain the specimen (e.g. using iodine) so the subcellular structures can be seen. Place a cover slip over the specimen to protect it

• Place the slide on the stage. Always start on the lowest magnification (makes it easier to focus & gives the widest field of view). Make sure the objective lens isn’t too close to the stage (avoids damage to the lens and slide)

• Focus the image

  Coarse adjustment knob: Moves the stage up and down, use to roughly focus

  Fine adjustment knob: Helps focus the image to see the finer details

What are the risks when using a light microscope?

• Care must be taken when looking down the microscope that the illumination is not too bright as eye damage could be caused

• Care when using microscope stains as some are harmful

• Care when handling coverslips and microscope slides as broken glass could cut skin

What is the practical for investigating the effect of pH on enzyme activity?

1. Set up a water bath at 35°C, place 3 test tubes of starch, amylase enzyme and pH buffer into the water bath until they are 35°C

2. Put two drops of iodine solution into each well of a spotting tile

3. Add 2cm³ of amylase solution and 1 cm³ of pH buffer to a test tube

4. Place 2cm³ of starch solution into the same tube. Mix the solution, then start a stop watch

5. Use a pipette to remove 2 drops of solution every 20 seconds from the test tube & put into a different well of the spotting tile

6. Repeat until the iodine solution stops turning black. Record the time this takes. Repeat at the same pH 3 times and calculate a mean

7. Repeat the above with different pH buffers

What are the variables regarding the practical for investigating the effect of pH on enzyme activity?

• Independent variable: pH buffer

• Dependent variable: time taken (seconds) for the starch to break down

• Control variable: temperature, concentration & volume of amylase enzyme

What are the risks of the practical for investigating the effect of pH on enzyme activity?

• Iodine solution is an irritant. If it touches the skin, it should be washed off

• Goggles should be worn at all times

What is the practical for investigating osmosis in potatoes?

1. Prepare samples of potato, a cork borer helps maintain thickness

2. Place the potato in different concentrations of sugar / salt solution, all for the same amount of time

3. Take measurements of mass and length of the potato samples before and after soaking them in the solutions

4. Dry the potato before weighing it to control the amount of water, ensuring you only record the mass of the potato not the excess water

What are the variables in the practical for investigating osmosis in potatoes?

• Independent variable: the concentration of sugar / salt in the water

• Dependent variable: the mass / length of the root vegetable after being in the water

• Control variables: temperature, volume of solution, surface area of the root vegetable

What are the risks in the practical for investigating osmosis in potatoes?

• Make sure that the potato is placed on a ceramic tile when using the cork borer - do not cut the potato cylinders

• Care must be taken when using the scalpel

• Wear eye protection when using chemical reactions