Practicals Paper 1

Question 1

Method for plant/animal cells

Microscopy

Answer 1

Animal:
Gently scrape inside of cheek with sterile cotton bud
Smear scarpings onto microscope slide
Place used cotton bud in a beaker of disinfectant
Place a drop of dilute methylene blue to stain cells
Place coverslip over cells, lowering it carefully to avoid air bubbles
Plant:
Peel a thin layer of cells
Gently place the sample onto the microscope slide
Stain sample with iodine
Cover sample carefully to avoid air bubbles

For both:
Place slide under low power lens of a microscope focusing carefully. Then switch to a high power and focus using fine adjustment
Note magnification used and draw in pencil 2 or 3 cells in detail

Question 2

Disinfectants

Answer 2

Wash hands before touching the petri dish

Divide the selaed plate into 5 equal sections using a marker pen to draw sections on the base of the petri dish

Using respective sterile forceps dip one paper disc into each of the disinifectant solution and allow excess solution to drip off

Place carefully onto the respective section on the agar plate

Place used forceps into beaker of disinfectant

Ensure discs are well spread out and not touching each other

Reseal plates with tape, ensuring there is no gap so oxygen can enter

Place plate upside down so condensation doesnt mess up the discs and below 25C

Remove plate from incubator and measure diameter of the zone of inhibition around each disk

Question 3

Osmosis

Answer 3

Method:
Collect 7 potato chips/Peel them

Place them on a tile and using a sharp knife, trim them all to the same length 2 cm

Pour different concentrations of salt/sugar sloution into 5 test tubes

Meausre mass of each potato chip record their mass on tabletop balance

Place them in the test tube and leave for 20 minutes

Remove the potato chip from the solution and place on a paper towel to remove excess liquid

Measure mass again and record the data

Question 4

Enzymes pH

Answer 4

Method:
Measure 10cm3 of strach solution using 10cm3 plastic syringe and place into the boiling tube

Measure 1cm3 of buffer solution using the 1cm3 plastic syringe then add this the starch solution

Measure 1cm3 of amylase solution using the 1cm3 plastic syringe and add this to a different test tube

Place both tubes in the water bath to warm up

Place one drop of iodine solution into each well of the spotting tile

Add the amylase solution to the starch solution and mix. Start the stopwatch

Take out a drop of the starch amylase mixture and add to a well in the spotting tile

Repeat this every 30 seconds until there is no change in colour or 5 minutes has passed

Repet steps 1 to 8 for different pH values

Question 5

Food tests

Answer 5

Method for all:
Use pestel and mortar to grind up food
Starch-
Place small piece of food to test on white tile
Add 2 drops of iodine solution to food
If iodine solution changes from orange to blue-black the food contains starch
Sugar-
Mix a small sample with 3cm3 of Benedicts reagent in a boiling tube
Heat the mixture in a hot water bath for 3 minutes
If solution changes from blue to a brick red colour the food contains sugar
Protein-
Mix with 3cm of biuret reagent
Leave for 2 minutes
If buiret reagent changes from blue to a purple colour the food contains protein
Lipid-
Mix food with few drops of Sudan III solution
Then solution should form red layer on top of clear solution if lipids present

Question 6

Photosynthesis

Answer 6

Method:
Place piece of pond weed in a beaker of water with a paper clip attached to it to stop floating

Add small quantity of sodium hydrogen carbonate to the water to supply carbon dioxide

Start with lamp 60 cm from the pond weed and count number of bubbles produced in a minute or for higher accuracy place gas syringe over beaker to measure volume of gas produced

Repeat 3 times

Move light closer to 50cm away from the beaker and repeat steps 3 and 4.

Repeat this process at a number of shorter distances

Question 7

Culturing Microorganisms

Answer 7

Sterilise Petri dishes and culture medium so that other micororganisms dont grow

Then place agar gel in petri dish

Pass inoculating loop through bunsen burner flame to kill microorganisms

Allow loop to cool then place loop into bacteria sample then gently rub the loop into the agar gel to spread microorganisms

Secure lid with tape but do not fully seal

Incubate at 25C to reduce risk of harmful pathogens growing

Store Petri dish upside down to prevent condensation from dripping onto the agar.