Core Practicals

Question 1

Investigate the effect of ph on an enzyme by using buffer solutions

Answer 1

• Cells produce a waste product called hydrogen peroxide
• it is toxic and so must not be allowed to build up in a cell
• cells therefore contain an enzyme called catalase which can break down hydrogen peroxide into water and oxygen which are harmless
• we can investigate the effect of PH on the rate of breakdown of hydrogen peroxide by catalase
• You can get plenty of catalase from potato cells. They just need to be blended with water and then filtered to make potato extract full of all the catalase from the cells
• We can then add this to various pH buffers and hydrogen peroxide and measure the bubble of oxygen produced per minute from the reaction,

Question 2

Surface area ti volume ratio practical

Answer 2

• 3 different sizes agar cubes with phenolphthalein
• place in hydrochloric acid which will diffuse into the cube and turn the indicator from pink to colourless
• as the size of the cube increases, the surface area to volume ratio increases
• the bigger cubes will still be more purple as they require a bigger surface area in order to rely on diffusion.

Question 3

Osmosis practical visking tube

Answer 3

• use a visiting tube to model how osmosis works on cells
• It is basically a permeable ,membrane that lets small molecules through but not large ones
• place 0.1% sugar solution in visiting tube and fill container in which visiting tube is in with 0.5% sugar solution
• water moves from inside the tube to outside of the tube.

Question 4

Osmosis practical potatoes

Answer 4

• use cork bearer to take 5 cores from potato
• cut off any skin
• use a ruler and scalpel to trim them all to 4cm
• blot the cylinders using paper towels to remove any excess water
• use a balance to record the mass of each cylinder
• Add each one to the following salt solutions and leave for 15 minutes
  
  1. Salt solution 0.0
  2. Salt solution 0.2
  3. Salt solution 0.4
  4. Salt solution 0.6
  5. Salt solution 1.0
• calculator % change in mass of the potato after 10 minutes in the solution
• potato in more concentrated solution will lose mass
• potato in less concentrated solution will gain mass

Question 5

How to prove photosynthesis produces starch

Answer 5

• remove a leaf from the plant
• place it in a beaker of boiling water for 30s to kill it

Place another leaf in a beaker of boiling water for 30s to kill it
- then place it in boiling tube of ethanol to remove the green pigment called chlorophyll from the leaf

• remove both leaves using forceps and put iodine over it.
• iodine will turn blue black if starch is present
• leaf in dark cupboard for 3 days will not go blue black because photosynthesis stopped occurring after chlorophyll was removed
• leaf not in dark cupboard§1q will turn blue black as photosynthesis is still occurring.
• you can prove this also by adding soda lime in a bell jar.
• the soda lime uses up the co2 so eventually the plant will stop photosynthesising and use up its starch reserves for energy
• therefore if you tested for starch it would not be positive

Question 6

Investigate the energy content in food

Answer 6

• weigh food sample
• place 20cm3 of water in a boiling tube
• measure temp of water
• light the food and hold it under the boiling tube
• continue this until it will no longer burn
• stir the water and measure the final temp
• (final temp - start temp) x 20x4.2/ mass of food + energy in J/g