Required Practical

Question 1

Explain how to prepare a food sample

Answer 1

1. Get a peice of food and break it up using a pestle and mortar
2. Transfer the ground up food to a beaker and add some distilled water
3. Mix the solution with a glass rod to dissolve some of the food
4. Filter the solution with filter paper to get rid of any solid bits of food and add to a testing tube

5.Add your different testing solutions to the testing tubes

Question 2

What are the Safety precautions for this required practical

Answer 2

• Do not eat any of the food in case of allergies
• Wear safety goggles when dealing with the solutions

-Be careful when dealing with the ethanol as it is flammable
Be careful when dealing with the buiret as it is an irritant

Question 3

How do enzymes work (7steps)

Answer 3

• Enzymes are protiens that sppeed up the rate of chemical reactions
• They have a specific shape called an active site
• The active site is complementary to the shape of a substrate molecule. Like a “lock and key”
• There are random collisions between the enzyme a substrate molecules and when an substrate molecule enetrs the enzymes active site an enzyme-substrate complex is formed
• Bond are broken in the substrate molecules
• Products are released
• The enzyme can then be reused

Question 4

How do you prepare a microscope slide

Answer 4

1. Use a dopping pippete to poor a drop of water onto the slide
   - Separate one of the thin layers of the onion
   - Peel off the layer of epidermal tissue from the inner surface
   - Using forceps Place the epidermal tissue into the water on the slide
   - Add two or three drops of iodine solution which is used as a stain to highlight the cell
   - Place a cover slip onto the cell. First place the edge kf the coverslip on the slide at a 90 degree angle . Then lower the coverslip gently with a mounted needle the slip so that no air bubbles get stuck under the cover as they could obstruct the view of the cell
   - Use a piece of blotting paper to remove any excess liquid from the slide
   - Put the prepared slide on the microscope stage

Question 5

Hoe do you use the light microscope to look at the slide (6 steps)

Answer 5

• carry the microscope with one hand on th earm and one on tne base
• Plug in and switch on the light source
• Clip the slide you have prepared onto the stage
• Select the lowest power objective lens
• Look down the eyepeice , use the coarse adjustment knob to move the stage up or down until the image is roughly in focus
• Adjust the fine adjustment knob until you get a clear view of what is going on on the slide
• repeat steps 5-6 with medium objective lens

Question 6

How do you plan a required practical for osmosis

Answer 6

1) Use a cork borer to cut five potato cylinders of the same diameter
2) Use a knife to trim off any potato skin on each cylinder. Then trim each potato cylinder so they are the same length
3) accuratley measure the mass (g) of each potato cylinder
4) Accuratley measure the length of each potato cylinder
5) Record the measurements in a table
6) Measure 10cm3 of each conc of sugar solution and put into boiling tubes. Label boiling tubes cleary
7) Measure 10cm3 of distilled water and put into fifth boiling tube
8) Add one potato cylinder to each boiling tube
9) leave boiling tubes for chosen amount of time
10) remove the potato cylinders and carefully blot them dry with paper towels to remive water
11) measure the new mass and length of each potato cylinder . Record results

Question 7

What is the independent variable

Answer 7

The concentration of sugar solution

Question 8

What is the dependent variable

Answer 8

The mass of the potato chip

Question 9

Describe a method to find out the rate of enzymatic activity

Answer 9

1. Put a drop of iodine solution into every well of a spotting tile
2. Place a bunser burner on a heat proof mat and a tripod and a gauze over the bunsen burner.Put a beaker of water on top of the tripod and heat the water till it is 35°
3. Use a syringe to add 1cm3 of amylase solution and 1cm3 of a buffer solution with a Ph of 5 to the boiling tube. Place the boiling tube into beaker of water and wait for five minutes
4. Using a different pippete add 5cm3 of startch solution into the boilimh tube .
5. Mix the content of the boiling tube and start stirring
   - use a dropping pippete to take a fresh sample of the amylase starch from the boiling tube every thirty seconds and put a drop into a well
   - When the idodine solution remains browny orange startch is no longer present
   - Repeat the experiment with buffer solutions of different PH values to see how PH affects the rate of reaction