Required Practicals Paper 1

Question 1

General tips (not a flashcard just read)

Answer 1

• Mention all the equipment
• State safety measures
• Remember variables
• State how you will get accurate data by reducing errors and uncertanties

Question 2

Parts of the microscope and their role

Answer 2

• Stage + clips - where the slide goes
• Lamp - passes light through the slide
• Objective lenses - lenses with magnifications of 4x 10x and 40x
• Eyepiece - where you look through and has a lense with 10x mag
• Coarse focus
• Fine focus

Question 3

How to prepare an onion cell slide

Answer 3

• Wash the onion and peel a one cell layer of skin using a scalpel and tweezers
• Clean slide and coverslip
• Put thin onion strip onto the slide and reposition using a toothpick
• Add a drop of iodine onto the onion - this stains the cells so they can be seen
• Slantly put the coverslip on so no air bubbles form

Question 4

How to use the microscope to view a prepared slide

Answer 4

• Put it on the stage and attach the clips to hold it in place
• Use the lowest power objective lens
• Turn the coarse focus dial until the lens nearly touches the slide
• Look through the eyepiece and slowly turn the coarse focus dial until the cells come into focus
• Use the fine focus dial to bring the cells into a clear focus
• Repeat using different objective lenses and turn the fine focus dial

REMEMBER, INCLUDE A MAGNIFICATION SCALE IN YOUR DRAWING

Question 5

How to grow bacteria in the lab

Answer 5

• Nutrient broth solution
• Agar gel plate with nutrients

Question 6

Aspetic technique to prepare an uncontaminated bacterial culture

Answer 6

• Sterilise petri dishes, nutrient broth and agar
• Sterilise the inoculating loop by passing it through a bunsen flame
• Inoculate the agar with the bacteria but only open the lid slightly so less airbourne pathogens can get in
• Do this near the bunsen flame to kill airbourne pathogens as they move towards the flame
• Add 2 pieces of Cellotape to the lid to stop bacteria entering, leaving and to allow oxygen to enter
• Label, store upside down (stop condensation falling) in an incubator at 25 degrees (prevent growth of harmful human pathogens)

Question 7

How to investigate the effect of an antibiotic on a bacterial growth

Answer 7

• Same method as before but add sterile filter paper disks with the antibiotic onto the plate
• After a few days, you should observe that around the antibiotics, there are no bacteria growing
• This is called the zone of inhibition
• The effefct of the antibiotic can be calculate using the area of the zone of inhibition

Question 8

How to investigate the effects of osmosis on plant tissue

Answer 8

• Peel the potato to remove the skin
• Use a cork borer to produce 5 potato cylinders with the same duameter and a scalpel to trim them to the same length
• Record the mass using a mass balance
• Add each potato cylinder to a test tube and add 10cm3 of distilled water, 0.2mol sugar solution with increases of 0.2 each time
• After 24hrs, remove the potatoes and gently roll them on a paper towel to remove excess water than hadn’t been absorbed (surface moisture)
• Record the new mass
• Find the percentage change and plot a graph

Question 9

How to prepare a sample of food for a food test

Answer 9

• USing distilled water, grind the food using a pestle + mortar to get a paste
• Transfer to a beaker, add water and stir so all the chemicals in the food dissolve in the water
• Filter the solution to remove suspended food particles
• This produces a food solution

Question 10

How to test for lipids

Answer 10

• Add a few drops of distilled water and ethanol
• Shake gently
• If lipids are present, a cloudy white emulsion forms

Question 11

How to test for carbohydrates

Answer 11

• Add iodine SOLUTION to the food solution
• If carbs are present, the iodine solution will turn form orange to blue-black

Question 12

How to investigate the effect of pH on amylase

Answer 12

• Place one drop of iodine solution into each well of a spotting tile
• Set up 3 test tubes - one with 2cm3 starch soltuion, one with 2cm3 amylase solution and the last with 5cm3 pH buffer solution (to control the pH)
• Place all test tubes in a 30 degrees water bath. Leave for 10 mins to equilibrate
• Combine all solutions, mix, return to water bath and start a timer
• At 30 second intervals, transfer one drop of solution to a well until the iodine remains orange
• Repeat the whole experiment using different pH buffers (6,7 and 8)
• Plot a graph which will be a curve and the lowest point is the optimum pH

Question 13

Problems with the pH amylase experiment

Answer 13

• 30 second samples may not be frequent enough so the time is only approximate
• The colour change tends to be gradual so it is hard to tell when the iodine isn’t blue-black

Question 14

Method for photosynthesis practical

Answer 14

• Place LED 10cm away from boiling tube
• Fill boiling tube with water and sodium hydrogen carbonate (release carbon dioxide)
• Add pondweed with cut end at the top and leave to acclimatise
• After 5 mins, start a stopwatch and count the number of bubbles produced in one minute
• Repeat to find a mean
• Repeat at different distances e.g. 20cm, 30cm

Question 15

Relationship between light intenisty and distance from light source

Inverse square law

Answer 15

• As distance increases, light intensity decreases
• Light intensity is proportional to the inverse of the distance from the light squared

Question 16

Control variables for photsynthesis practical

Answer 16

• Temperature
• Type of light source
• Concentration of bicarbonate
• Piece/species of pondweed

Question 17

Problems with the photosynthesis and the solution

Answer 17

• Bubbles may be too fast to count accurately
• Bubbles aren’t the same size so a small bubble would be the same as a large bubble even though the large bubble has more oxygen
• This is fixed by using an inverted measuring cylinder filled with water to measure the volume of oxygen produced in a set amount of time