Required practicals paper 1

Question 1

RP-microscopy

Answer 1

-place the slide onto the stage,using the clips to hold it in place
-select the lowest power objective lense
-position the lens so it almost touches the microscope slide by turning the course focusing dial whilst looking from the side
-look down the eyepiece,then slowly turn the course focussing dial until the cells come into focus
-then we use the fine focusing dial to bring the cells into clear focus

Question 2

RP-osmosis in potatoe

Answer 2

-peel potato skin
-use a cork borer to produce three cylinders of potato
-use a scalpel to trim potato to equal lengths(around 3cm)
-measure the length(using ruler) and mass(use balance) of potato
-now place each cylinder into a test tube,add 10cm^3 of a 0.5 sugar solution into the first test tube
-add 10cm^3 of 0.25 molar sugar solution to second test tube and 10cm^3 of distilled water to the third
-leave the potato cylinders over night to allow osmosis to take place
-remove potato cylinders rolling them on paper towel removing surface moisture
-measure the length and mass of the potatoes once again
-calculate % change of mass and length

Question 3

RP-Food tests

Answer 3

-take food sample and grind with distilled water using mortar and pestle,making a paste
-transfer the paste to a beaker and add more distilled water,stir so the chemicals in food dissolve in water
-filter the solution to suspend any food particles

Question 4

RP food test for starch

Answer 4

-place 2cm^3 of food solution into test tube
-add a few drops of iodine solution which is orange
-if starch is present the solution will turn blue/black

Question 5

RP testing for sugars

Answer 5

-place 2cm^3 of food solution into test tube
-add 10 drops of blue benedict’s solution
-place the test tube into a beaker and half fill the beaker with hot water
-leave the beaker for around 5 minutes
-if sugars are present the benedict’s solution will change colour
-green=small amount of sugar
-yellow=more sugar present
brick red=a lot of sugar present
-only works for reducing sugars

Question 6

RP testing for protein

Answer 6

-place 2cm^3 of food solution into test tube
-add 2 cm^3 of blue biuret solution
-if protein is present the solution will turn purple/lilac

Question 7

RP testing for fats/lipids

Answer 7

-place 2 cm^3 of food solution into test tube,however this solution is not filtered
-add a few drops of distilled water and a few drops of ethanol, gently shake the solution
-if lipids are present white cloudy emulsion forms

Question 8

RP for PH on enzymes

Answer 8

-place one drop of iodine solution into each well of a spotting tile
-take three test tubes,first one has 2cm^3 of starch solution
-second test tube has 2cm^3 of amylase solution
-third test tube has 2cm^3 of pH 5 buffer solution
-place all three test tubes into a water bath at 30’c,leave them for 10 minutes to allow solutions to reach correct temperature
-combine all three test tubes into one test tube and mix with a stirring rod, return to the water bath and start a stop watch
-after 30 seconds use the stirring rod to transfer one drop of solution to a well,iodine should turn blue black showing starch is present
-take another sample every 30s until iodine keeps orange
-record the time
-repeat experiments different pH buffers

Question 9

problems for RP pH on enzymes

Answer 9

-by only taking samples every 30s we only have an approximate time for the reaction to complete
-we can fix this by taking samples every 10 seconds
-not always obvious when it turns blue/black
-can address this by having multiple people overlook the experiment

Question 10

RP photosynthesis

Answer 10

-start by taking a boiling tube and placing it 10 cm away from an LED light source
-fill the boiling tube with sodium hydrogen carbonate solution,this releases carbon dioxide which is needed for photosynthesis
-place a pond weed into the boiling tube with the cut end at the top
-leave this for 5 minutes to acclimatise to the conditions of the boiling tube
-should see bubbles of gas being produces from the cut end
-this gas is oxygen being produced through photosynthesis
-start stop watch and count number of bubbles per minute
-repeat 2 more times and calculate mean
-do the whole experiment again at 20,30,40cm

Question 11

what is the problems with the photosynthesis practical and how do we fix them

Answer 11

-number of bubbles can be too fast to count accurately
-the bubbles are not always the same size,a small bubble would count the same as a large bubble

-we can fix these issues by measuring volume of oxygen produced instead of counting bubbles
-we do this by placing pond weed under a funnel and catch the bubbles in a measuring cylinder

Question 12

the graph of photosynthesis equation is effected by what law

Answer 12

-inverse square law
-if we double the distance the light intensity falls by four

Question 13

how to prepare a microscope slide for onion

Answer 13

-peel one cell thick layer of onion using a scalpel and tweezers
-place this on a microscope slide,add a drop of iodine to stain the cell,place a cover slip on top, and place on the microscope stage