Required practicals- paper 1

Question 1

What is the method for using a light microscope?

Answer 1

1. Collect sample of tissue you want to observe.
2. Remove inner layer of onion using forceps, or a thin layer of algae using the scalpel.
3. Place the thin slice onto a clean glass slide
4. Using a pipette, add one or two drops of dilute iodine solution to the top of the onion skin/ slice of algae plant.
5. Hold the coverslip by its side and lay one edge of the coverslip onto the microscope slide near the speciemen.
6. Lower the coverslip slowly so that the liquid spreads out.

Question 2

What is the method for testing osmosis in plants?

Answer 2

1. Create three potato bores of equal mass.
2. Place the potato bores in 3 types of solution: pure water (0M), slightly salty water (0.3M), very salty water (0.8M).
3. Leave for 30 mins.
4. Remove and dry them, re-weigh to record their final mass.

Question 3

What is the method for investigating the impact of pH on amylase?

Answer 3

1. Take five different different test tubes and half-fill them with amylase.
2. Add a range of pH buffers to each test tube until each test tube is 3/4 full (pHs ranging 1-14 eg. 4,6,8,10,12)
3. Add starch solution to fill the test tubes.
4. Swirl gently to mix the solutions together.
5. Immediately start the timer.
6. Every 30 seconds use a pipette to remove some of the mixture from each of the five test tubes. Place the 5 solutions into a spotting tile.
7. Add iodine solution to the drops made, if the drop turns from yellow- red to blue-black, then the amylase has not worked yet as there is still starch present.
8. Repeat steps 6 and 7 until the iodine doesn’t turn blue/black. This may happen faster for some solutions than others.

Question 4

What is the method for preventing bacterial growth?

Answer 4

1. Get an agar plate and draw a cross on the bottom of it using a marker pen, splitting it into quarters.
2. Label each quadrant a different antibacterial (e.g. mouthwash, bleach etc.)
3. Use a bacterial spreader to spread a bacteria colony onto the agar.
4. Dip a small paper disc into one of the three antibacterials and carefully place into the middle of the quadrant on the agar gel.
5. Make sure one paper disc isn’t dipped into anything, this is used as a control.
6. Place the agar plate into an incubating oven set to a maximum of 25°C and wait a week.
7. A week later take out the agar plate and measure the diameter of the zones of inhibition to see which antibacterial was the most effective.

Question 5

What is the method for testing how light affects the rate of photosynthesis?

Answer 5

1. Take some pondweed and place it in a boiling tube.
2. Use a thermometer to measure temperature in boiling tube (control variable).
3. Place the lamp 15cm away. Place a large beaker of water between the lamp and the boiling tube.
4. Wait until a steady flow of bubbles comes from the end of the pond weed before you count how many bubbles are produced in 2 minutes.
5. Repeat steps 2-4 but changing the distance that the lamp is from the pond weed.

Question 6

How would you test for starch?

Answer 6

1. Grind up the food being tested to increase surface area.
2. Drop yellow-red iodine solution into the food being tested.
3. If it turns blue-black then starch is present.

Question 7

How would you test for sugars (glucose)?

Answer 7

Benedict’s test
1. Grind up the food being tested to increase surface area.
2. Add blue Benedict’s solution onto the food being tested.
3. Heat the solution.
4. If it turns brick red then sugar is present.

Question 8

How would you test for protein?

Answer 8

Biuret’s test
1. Grind up the food being tested to increase surface area.
2. Add blue Biuret’s solution to food being tested.
3. If it turns purple then protein is present.

Question 9

How would you test for lipids?

Answer 9

Ethanol test (Emulsion test)
1. Grind up the food being tested to increase surface area.
2. Add clear ethanol to food being tested.
3. If a cloudy white layer is formed then lipids are present.
4. HAZARD- Ethanol is highly flammable and harmful!

Question 10

How would you prepare a petridish to make sure it’s an uncontaminated culture of bacteria?

Answer 10

• Petri dish should be heated to sterilise beforehand in order to kill any unwanted microorganisms
• An inoculating loop used should be passed through a flame first in order to sterilise it
• After transferring the bacteria, the lid of the petri dish should be lightly taped on- to stop microorganisms in the air from getting in
• The dish should be stored upside down to stop drops of condensation falling onto the agar surface.