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• they should avoid contact with hands/skin and they could also wear gloves [1]
• they should wear safety googles [1]
• they should wash their hands after handling the bottle or slide, or (of course) not drink the stain [1]

1. take an onion bulb and remove one of the leaves
2. peel a piece of inner epidermis from the leaf using forceps
3. trim the piece of epidermis and place in one drop of water on a microscope slide
4. lower a coverslip on top, taking care not to trap any air bubbles
5. place one drop of iodine solution next to the coverslip
6. draw the iodine solution under the slide by placing a piece of filter paper on the other side of the coverslip

[6]

These are the main points that the examiner will be looking for, but you do not have to match every word.

In questions based on compulsory practical activity groups, the examiner will make allowances for instances where the equipment used in one school may be slightly different from another, the level of detail you've added, or if your answer is worded in a slightly different way.

1. select the lower power objective
2. move the stage as close to the objective as possible
3. place the prepared slide on the stage
4. focus away from the slide, using the coarse focusing adjustment, until the specimen is in focus
5. move the high power objective in line with the slide
6. use the fine focusing adjustment to bring the specimen back into focus
7. if the specimen cannot be brought back into focus, refocus under low power and repeat steps 5-6

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Note: This is a 6 mark question so only answers that have a logical sequence with relevant detail would achieve six marks. Allow marks for variations in enzyme chosen, method, solutions and volumes.

The below example is for the digesting of starch by amylase.

Answer six from:

1. Prepare a water bath at 35°C - this is a suitable temperature for the enzyme to work.
2. Put two drops of iodine solution into each spot of a spotting tile so that starch can be tested for.
3. Set up test tubes for a range of pHs using the appropriate buffer solution to control the pH.
4. Place 5 cm³ of amylase and 10 cm³ of starch solution into one of the buffer solutions - start timing immediately because the reaction starts as soon as everything is mixed.
5. Mix the solution in the test tube so that the amylase and starch can react fully/predictably and place it into the water bath.
6. Use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile. This is done at short time intervals because the reaction might be fast/to be able to tell the different pHs apart.
7. Repeat until the iodine solution stops turning black/remains orange. At this point all of the starch has been digested
8. Repeat the experiment for each pH and compare the times. The one where the iodine no longer turns black/remains orange in the shortest time has the fastest rate of reaction.
9. Carry out the entire investigation at least twice to check repeatability.

[6]