Paper 1 Required Practicals

Question 1

PRACTICAL 1: MICROSCOPES

• What is the centre of the microscope called?
• What is below the centre of the microscope?
• What is above the centre?
• How do we use a microscope to view a prepared slide?

Answer 1

• The stage
• The Lamp/Mirror
• The optical lenses
• 1) Place the slide onto the stage
  2) Use clips to hold slide in place
  3) Select lowest magnification lens
  4) Use the coarse focusing dial to adjust the height
  of the lens. View from side so we can see clearly.
  5) Look down the eye piece and move coarse
  focusing dial until image is focused
  6) Use fine focusing dial to bring cells into CLEAR
  focus
  7) Use a pencil to create a detailed image

Question 2

PRACTICAL 2: CULTURING MICROORGANISMS

- How do we investigate bacterial growth?

Answer 2

• 1) Clean bench with disinfectant solution to kill
  microorganisms
  2) Sterilise inoculating loop by passing through flame
  3) Open sterile agar gel plate near a bunsen burner
  4) Use loop to spread bacteria evenly
  5) Place sterile filter paper discs soaked in
  antibiotics onto the plate
  6) Incubate at 25°C, leave for a few days

Question 3

PRACTICAL 3: EFFECT OF OSMOSIS

- How do we investigate the effect of osmosis?

Answer 3

• 1) Peel the potato
  2) Produce 3 cylinders of equal diameter and same
  length using a cork borer and a knife
  3) Measure length and mass of each cylinder
  4) Place each cylinder into a test tube - add 10cm^3
  of 0.5 molar sugar solution to the first, 10cm^3 of
  0.25 molar to the second, and 10cm^3 of distilled
  water to the 3rd as a control
  5) Leave cylinders over night
  6) Remove potato cylinders and dry them on paper
  towel
  7) Measure mass and length. Calculate percentage
  change (change in value ÷ original value x 100)

Question 4

PRACTICAL 4: FOOD TESTS
- How do we carry out food tests for carbohydrates,
proteins and lipids?

Answer 4

• 1) Take the food sample and grind with water using
  mortar and pestle
  2) Transfer paste to beaker and add more water - stir
  so chemicals dissolve
  3) Filter to remove suspended food paticles
  4) Starch: Add 2cm^3 of food solution and 2 drops of
  iodine solution if starch is present, iodine will turn
  blue-black. If not it will remain orange

  Sugars: Add 2cm^3 of food solution and 10 drops 
  of benedicts solution. Place tube into beaker and 
  half fill with hot water.  Leave for 5 mins.  If 
  solution turns brick-red sugar is present.
  
  Protein: Add 2cm^3 of food solution and 2cm^3 of 
  bieuret solution.  If it contains protein, solutions 
  turns from blue to pink
  
  Lipids: Add 2cm of food solution.  Add ethanol, if 
  solution turns cloudy, lipids are present

Question 5

PRACTICAL 5: EFFECT OF PH ON AMYLASE

- How do we test for the effect of pH on amylase?

Answer 5

• 1) Place 1 drop of iodine solution into each well of a
  spotting tile
  2) Take 3 test tubes - In the first, 2cm^3 of starch
  solution, the second 2cm^3 of amylase solution,
  the 3rd 2cm^3 of a pH 5 buffer solution
  3) Place all 3 in a water bath at 30°. Leave for 10
  minutes
  4) Combine the 3 and return into water bath and
  start a stopwatch
  5) Each 30 seconds, take a drop using a stirring rod
  and add to the iodine
  6) When the iodine no longer turns blue-black, all
  the starch has been broken down by the amylase
  7) Repeat with other pH levels and compare the
  times

Question 6

PRACTICAL 6: PHOTOSYNTHESIS

- How do we investigate the rate of photosynthesis?

Answer 6

• 1) Place a boiling tube 10cm away from an LED light
  source
  2) Fill with sodium hydrogen carbonate solution
  which releases CO2
  3) Add pond weed with cut end at top and leave for
  5 mins
  4) Start a stopwatch and count the number of
  bubbles produced in 1 minute. Repeat 2 more
  times and calculate a mean.
  5) Complete experiment again but 20cm away, then
  30cm and 40cm away
  6) If we double the distance, the mean number of
  bubbles falls by 4