Biology P1 - Practicals

Question 1

How do you use to test for glucose?

Answer 1

• Benedict’s solution
• Heat in water bath
• Will turn from blue to green/yellow/red depending on glucose quantity

Question 2

How do you use to test for starch?

Answer 2

• Iodine
• Yellow/brown to blue/black

Question 3

How do you use to test for proteins?

Answer 3

• Biuret’s reagent
• Add biuret solution A to the food solution
• Mix liquids
• Add biurets solution B

Question 4

How do you test for lipids?

Answer 4

THE SUDAN III TEST
- Equal amounts of food and water are added to a test tube, Sudan III is added and it is shaken
- A red layer forms on the surface of the water
THE EMULSION TEST
- Ethanol is added to a test tube containing crushed food
- Poured into a test tube, leaving any food residue behind
- Cloudy liquid (emulsion) indicates the presence of lipid in the food

Question 5

Describe the microscopy practical:

Answer 5

• Cut a section of onion 1 cell thick and place on microscope slide.
• Add drop of iodine and place cover slip
• Place slide onto microscope stage
• Turn on light
• Start on lowest magnification and use the coarse focus and fine focus knob. Increase magnification if needed

Question 6

Describe the osmosis practical

Answer 6

• IV = concentration of sugar solution
• DV = percentage change in mass
• Controls = temperature, same potato
• Cut equal size cylinders from a potato with a corer and remove any skin with scalpel
• Dab with paper towel to remove excess water
• Place on a top-pan mass balance to measure it’s mass
• Place potato cylinders in different sugar solutions and leave for set amount of time (eg. 1 day)
• Remove and dab off any excess water with paper towel
• Measure mass again with top-pan mass balance
• Calculate change in mass with: (final mass - initial mass) / initial mass * 100
• Plot this against concentration and where LOBF meets x-axis: concentration in potato - No water in or out

Question 7

Describe the Enzymes practical

Answer 7

AIM - determine the optimum temp/pH

• IV = temperature OR pH
• DV = time for substrate to be broken down
• Measure out the enzyme and substrate (e.g. starch and amylase)
• Place separately in water bath, along with buffer solution if changing pH
• Prepare a spotting tile with iodine drops
• Mix the reactants together and start timer
• Every 10 seconds remove a drop of the mixture and place in dimple with iodine. If it changes colour there is still starch
• Repeat for different temperatures/pH and plot these times against temperature/pH and draw a line of best fit. The optimum condition les between the two lowest points

Question 8

Describe the food tests

Answer 8

• Make solution by grinding solid food and adding distilled water

STARCH
- Turns IODINE from ORANGE to BLACK

GLUCOSE
- Turns BENEDICT’s SOLUTION from BLUE to Green, Yellow, Orange, or Brick Red when heated in water bath

PROTEIN
- Turns BIURET’s REAGENT from BLUE to PURPLE

LIPIDS (FATS)
- Add COLD Ethanol, then shake with water - it will turn cloudy
- OR Sudan III forms two layers - top brick red

Question 9

Describe Photosynthesis practical

Answer 9

IV - distance between plant and light source
DV - rate of photosynthesis (indicated by O2 produced)

• Put pond weed in test tube and add sodium hydrogen carbonate and cut stem at angle while submerged.
• Invert and put in a beaker, ensuring there is no air at the top
• Carry out in dark room
• Position lamp at a distance measured with a meter ruler
• Wait 1 minute for plant to acclimatise to light
• Start stop-clock and count how many bubbles, or measure the volume of O2 produced in 1 minute
• Change distance and repeat, plotting rate ( bubbles/volume) against distance.
• Inverse square relationship with distance