Biology Practicals

Question 1

Plan an experiment to view onion cells under a microscope

Answer 1

1. Use a dropping pipette to put one drop of water onto a microscope slide.
2. Separate one of the thin layers of the onion.
3. Peel off a thin layer of epidermal tissue from the inner surface.
4. Use forceps to put this thin layer on to the drop of water that you have placed on the microscope slide.
5. Make sure that the layer of onion cells is flat on the slide.
6. Put two drops of iodine solution onto the onion tissue.
7. Carefully lower a coverslip onto the slide. Do this by placing one edge of the coverslip on the slide and then using a mounted needle to lower the other edge onto the slide.
8. Use a piece of filter paper to soak up any liquid from around the edge of the coverslip.
9. Put the slide on the microscope stage

Question 2

Plan an investigation to culture a group of microorganisms

Answer 2

Microorganisms
1.Try to work next to a bunsen burner
→ Creates asephic environment to kill 2.Heat agar plate in an autoclave
surrounding microorganisms.
→ kills any microorganims present
3.Use sterile inoculating loop to transfer bacteria to agar plate
→ pass it through hot flame.
4.Carfully Spread bacteria around surface of agar plate
→ even spread of bacteria
5 Close petri dish and lightly tape sides
→ avoids microorganisms entering.
6.Place petri dish upside down
→ prevents condensation dropets falling on agar jelly.
7.leave pate at 25°C to allow cultue to grow
→ harmful pathogens grow above this
8.After some time, you should notice colonies forming on surface of agar jelly.

Question 3

Plan an investigation in order to find the concentration of a cylinder of potato

Answer 3

1.Use cork borer to cut 5 potato cylinders of same diameter
2.Use scalpel and ruler to trim each potato so they are all 3cm
3.Measure each mass and record in a table of results
4.Measure 10cm3 of each sugar solution and pour into each boiling tube
5. Add one potato into each one and wait for 30 minutes
6.After 30 minutes remove the potatoes and dry using paper towel
7.Record final mass of each and record in a table of results.
8.Plot a graph of concentration against percentage change in mass.
9.Where the line hits 0% is the concentration of the potato

Question 4

Plan a test to identify if foods contain starch, sugar, protein, lipids

Answer 4

Iodine tests for starch
1.Put food sample in test tube
2. Add a few drops of iodine
3. Is starch is present then solution will turn blue-black

Benedict’s test for sugar
1. Add 5cm3 Benedict’s solution into test tube with food sample
2. Place in hot water bath for 5 min
3. If sugar is present then solution will turn brick red

Biurets test for protein
1. Add food sample into test tube and a few drops of biurets
2. Shake vigorously and wait 5 minutes
3. If protein is present then the solution should turn lilac

Ethanol test for lipids
1. Add 3cm3 of ethanol into the test tube
2. Pour into a test tube of equal amounts of water
3. If lipids are present the solution should turn cloudy

Question 5

Plan an investigation to figure out how long it takes for amylase to react

Answer 5

1. On a spotting tile add a drop of iodine solution on each well
2. Add 2cm3 of buffer solution using a a syringe into each test tube
3. Immerse the starch and amylase solution and test tubes of buffer solution into hot water bath
4. Allow the temperatures to equilibrate
5. Add 2cm3 amylase solution into buffer solution test tube
6. Add 2cm3 of starch solution into the same test tube and start timer
7. Use glass rod to transfer a drop of the mixture into the well
8. Repeat 6-7 until there is no colour change
9. Calculate rate of reaction by doing 1/time taken
10. Repeat 2-8 using different pH
11. Plot a graph of rate of reaction against pH

Question 6

Plan an investigation to show how light intensity affects the rate of photosynthesis

Answer 6

1. Place test tube rack containing
   boiling tube 10cm from light
2. Fill boiling tube with 10cm3 sodium hydrogen carbonate
3. Place cut pondweed in boiling tube with cut end at the top. Push pondweed down using glass rod
4. Leave boiling tube to rest for 5 minutes
5. Start stopwatch and count the number of bubbles in one minute
6. For each distance repeat 3 times and take mean
7. Record in table
8. Repeat 1-7 for 3 more distances (20, 30, 40)
9. Plot graph of rate of photosynthesis against light distance
   →light intensity= 1/ distance^2