Paper 1 practicals

Question 1

Microscope

Answer 1

Prepare the slide:
-spread the cell on a slide and add a dye(iodine) to stain the cells and place a cover slip on top.

Place the slide on the stage and use grips to keep in place.

First select the lowest magnification objective lens.

Use the coarse focus wheel, then the fine focus wheel to focus on the image.

Draw the image using a pencil. Label parts. Write the magnification on the image.

Then change the lens to a higher magnification and re-focus the image.

Question 2

Microscope 2

magnification equation

Answer 2

Magnification= image size/real size

mm>μm = x1000

Question 3

Osmosis

Answer 3

Cut out 3 identical cylinders of a vegetable such as potato. Using a cork borer.

Measure length and mass of cylinders.

Place these columns of potato into test tubes and then add 10cm³ of different concentrations of sugar solution (0 mol / dm3, 0.5mol / dm3 and 1 mol / dm3).

Leave overnight.

Remove cylinders and remove surface moisture by rolling on a towel.

Measure length and mass of cylinders again.

Then…Calculate percentage change using…

change/original x100

Question 4

Effect of the ph on amylase

Answer 4

Prepare a spotting tile by dropping a couple of drops of iodine into each well.

Heat a water bath and place a boiling tube inside containing: -2cm³ starch
-2cm³ amylase
-2cm³ ph5 buffer
and leave for 5 mins

Now combine all 3 solutions into 1 test tube and mix with a rod. Return to water bath and start stopwatch.

After 30 seconds transfer one drop of solution to well in tile. The iodine turns blue/black if starch is present.

Now take sample every 30 seconds until iodine remains orange (orange=starch not present) Repeat with different ph buffers.

Question 5

Food tests

Answer 5

Test for sugars

Benedict’s test

• prepare food sample and transfer 5cm³ to test tube
• set water bath to 75℃
• add Benedict’s solution and leave for 5 mins

If sugar is present it will go from blue to green, yellow or red

Test for starch

Iodine test

• prepare food sample and transfer 5cm³ to test tube
• add a few drops of iodine solution and shake

If starch is present the colour will go from browny-orange to black or blue-black

Test for proteins

Biuret test

• prepare food sample and transfer 2cm³ to test tube
• add 2cm³ of biuret solution and shake

If protein is present it will go from blue to pink or purple

Test for lipids

Sudan III test

• prepare food sample and transfer 5cm³ to test tube
• add 3 drops of Sudan III stain solution and shake

If lipid is present the mixture will separate out into 2 layers, the top layer will appear red

Question 6

Photosynthesis

Answer 6

Place boiling tube 10cm away from LED light sourse

Fill tube with sodium hydrogen carbonate solution

Put a piece of pondweed into tube and cut off the end

Leave for 5 mins to adapt to conditions in the tube

Should see bubbles of gas being produces, this gas is oxygen

Start stopwatch and count number of bubbles in one minute

Repeat 3 times and calculate the mean

Complete experiment again but with the pondweed at 20cm then 30cm then 40cm

Light intensity = 1/d²