Experiments

Question 1

How to use a light microscope

Answer 1

Plug in + turn on
Use lowest lens 1st
Secure slide with clips
Use course focus to bring objective lens as close as possible
Refocus each time that you change lens power
Draw diagrams

Question 2

Examining onion cells

Answer 2

Set up microscope
Place water drop on slide
Place layer of epidermal onion tissue on slide with small paintbrush
Place cover strip at 45° to prevent air bubbles
Dry + examine under microscope
Repeat using iodine instead of water

Question 3

Examining cheek cells

Answer 3

Set up microscope
Swab inside of cheeks with cotton swab + wipe on slide
Cover with water drop
Place cover strip at 45° to prevent air bubbles
Dry + examine under microscope
Repeat using methylene blue instead of water

Question 4

To demonstrate osmosis

Answer 4

Soak 2 strips of visking tubing in water
tie a knot at 1 end of each
Fill 1 with distilled water + the other with sucrose + water solution
Tie each end + dry + find mass
Place each tube in a beaker with a rod supporting them
Leave for 15 mins + find new mass

Question 5

To test for reducing sugar

Answer 5

Dissolve glucose + water in test tube.
Add an equal volume of Benedict’s
solution (which is blue)
In test tube 2 mix water + Benedicts solution as a control.
Heat the test tubes in a boiling water bath.
Solution turns red if sugar is present and stays blue if not.

Question 6

To test for starch

Answer 6

Add iodine drops to starch+ water mix.
Add a few drops of iodine solution to water as a control
Blue black if starch is present

Question 7

To test for fat

Answer 7

Rub a butter on brown paper.
Repeat with water on brown paper as a control
Leave the paper to dry and examine for translucent stains.

Question 8

To investigate the effect of pH on the rate of enzyme activity

Answer 8

1) pH9 4 buffer solution + one drop of washing-up liquid + celery solution in graduated cylinder
2)Add hydrogen peroxide to a
smaller graduated cylinder
3)Both graduated cylinders in a water bath, wait then mix
4) Repeat steps 1-9 using pH buffers 7,10 and 13.

Question 9

To investigate the effect of temperature on the rate of
enzyme activity

Answer 9

1) Place pH9 buffer + 1 drop of washing up liquid + celery solution in graduated cylinder
2 )Add hydrogen peroxide to 2nd graduated cylinder
3)Stand in ice bath until 0°C
4)Mix solutions + record foam produced
5) Repeat at room temp and boiling