required practicals

Question 1

Describe a practical in which you would prepare a slide and observe it in a light microscope.

Answer 1

preparing a slide:

1) add a drop of water to middle of clean slide
2) use tweezers to place specimen onto water
3) add a drop of iodine solution to stain it
4) place a cover over and make sure there are no air bubbles

observing a slide:

1) place slide onto stage and attach with clips
2) select lowest power objective lens
3) use coarse adjustment knob to move stage just below lens
4) look into eyepiece and use coarse adjustment knob until focused
5) keep focusing with fine adjustment knob

Question 2

Describe a practical in which you would culture microorganisms on a petri dish or a broth, and investigating the effects of antibiotics.

Answer 2

culturing microorganisms:

1) sterilise petri dishes or broth to kill unwanted microorganisms and prevent contamination
2) sterilise inoculating loop in Bunsen burner flame
3) transfer organism onto loop and then to the dish with Bunsen burner nearby to kill bacteria in the air
4) attach lid to petri dish with adhesive tape to stop the lid from falling off and unwanted microorganisms entering
5) store upside down to stop condensation falling onto jelly. store at 25 degrees to avoid harmful bacteria

if investigating antibiotics:

• place paper discs with antibiotics onto plate before attach lid
• have a normal paper as a control
• area of no bacteria around disc is zone of inhibition

Question 3

Describe a practical to investigate the effects of osmosis.

Answer 3

effects of osmosis:

1) peel potato as the skin affects osmosis
2) use cork borer to produce three identical cylinders of potato, cut each to same length
3) measure length and mass of each
4) place each in a test tube and add each with 10 cubic cm of: pure water, concentrated sugar solution, in between
5) leave for 24 hours
6) remove and gently roll on paper towel to reduce moisture from surface
7) measure length and mass again

% change = (change / original) x 100

Question 4

Describe a practical to investigate the effect of pH on enzymes.

Answer 4

effect of pH on enzymes:

1) place one drop of iodine into each well on splotting tile
2) heat water in beaker to 35 degrees and try to keep constant
3) with a syringe, add 1 cubic cm of pH 5 Buffer solution to boiling tube, put in beaker and wait 5 minutes
4) with a syringe, add 5 cubic cm of starch to same boiling tube, mix and start stopwatch
5) at same intervals, take sample and drop into well
- if iodine stays brown-orange, no starch
- if iodine goes blue-black, starch
6) repeat with different pH Buffer solutions

Question 5

Describe practicals to test for starch, sugars, proteins and lipids.

Answer 5

food tests:
for all - take food sample and grind with morter and pestle, transfer to beaker, add distilled water, stir and filter and place in test tube

starch
- add a few drops of iodine (irritant to eyes) - starch = blue-black
no starch = brown-orange

sugars
- add 10 drops of Benedict’s solution (blue), place into beaker with hot water and leave for 5 minutes
high sugar - red - yellow - blue - low sugar

proteins
- add 2 cubic cm of Biuret solution (contains dangerous chemicals) and mix
if protein, purple-pink

lipids
- add 3 drops of Sudan III (contains flammable ethanol) and mix
if lipids, red stained oil layer will separate on surface

Question 6

Describe a practical on how to investigate the rate of photosynthesis.

Answer 6

rate of photosynthesis:

1) place boiling tube 10cm away from LED light
2) fill tube with sodium hydrogencarbonate solution as it releases carbon dioxide for photosynthesis
3) place pond weed in with cut end at top end
4) leave for 5 minutes to acclimate to conditions
5) start stopwatch and count bubbles produced in 1 minute
6) repeat 2 times for mean
7) repeat but at 20-50cm

• use LED as doesn’t release much heat
• if only normal bulb, place beaker of water between light and tube as it absorbs the heat