Biology paper 1

Question 1

Microscopy

Answer 1

• peel one layer of skin/cells from an onion using a scalpel and tweezers
  -place on a slide and add two drops of iodine to stain the cells
  -place coverslip on top making sure there are no air bubbles
  -place on microscope stage and turn on light so it reflects through condenser to the slide
  -use the lowest magnification objective lens. use coarse and fine focus knobs to focus. adjust magnification and focus if needed
  -place a ruler (graticule) to allow you to measure length of cells in micrometers
  I=AM

Question 2

Microbiology

Question 3

Osmosis

Answer 3

-cut equal size cylinders from potato (no skin) could use cork borer
-remove excess water from surface and weigh
-place each in a test tube with different concentrations of sugar solution and leave for a set time
-remove potatoes from test tubes and remove excess water, reweigh and calculate change in mass
change in mass%= change in mass/inintial mass X 100

Question 4

Enzymes

Answer 4

-measure out the enzyme and substrate (starch and amylase) place separately in a water bath (along with buffer solution if changing pH)
-prepare a spotting tile with iodine drops, mix reactants (starch and amylase)together and start timer.
-every 10 sec remove a drop of mixture and put in dimple of iodine, if it changes colour there is still starch present (once all the starch is broken down it will no longer change colour)
-repeat process for different temps or pH buffer solutions
-optimum condition lies between the two lowest points

Question 5

Food tests

Answer 5

-put grinded samples in a test tube with distilled water
- Starch: add iodine solution turns solution from orange/brown to blue/black
- sugar: add excess volume of Benedicts solution to food sample. place in ht water bath for a few minutes. if solution remains blue no sugar is present, if it turns brick red there is sugar. could also turn green, yellow,orange
-protein:add burets reagent and shake, if protein is present solution turns from blue to purple
-lipids (fats): add a few drops of ethanol to food sample add this to equal volumes of distilled water. if lipids present a white emulsion is formed (emulsion test)

Question 6

Photosynthesis

Answer 6

-put pond weed in test tube or measuring cylinder, add sodium hydrogen carbonate then cut stem at angle
- set lamp at set distance away from test tube, wait one minute then time one minute and count how many bubbles produced or measure volume of oxygen produced
-change distance and repeat