Practicals (Paper 1)

Question 1

What safety precautions should be taken when using a light microscope?

Answer 1

• Always start with the lowest power objective under the eyepiece
• Clip the slide securely on the stage
• Adjust the light source (mirror) so that light goes up through the slide

Question 2

What does the coarse focusing wheel do on a microscope?

Answer 2

Used to focus on the slide

Question 3

Where does the cell you are drawing need to be in relation to the slide?

Answer 3

In the middle

Question 4

What is the fine focusing wheel used for?

Answer 4

To focus on the cell

Question 5

When should you not use the coarse focusing wheel?

Answer 5

When you are using a higher powered objective as the the objective could crash into the slide

Question 6

What does the slide go onto?

Answer 6

The stage

Question 7

What do you look down on a microscope?

Answer 7

The eyepiece

Question 8

What is the bit under the stage?

Answer 8

The mirror

Question 9

What is the bigger wheel?

Answer 9

The coarse focusing wheel

Question 10

What is the smaller wheel?

Answer 10

The fine focusing wheel

Question 11

What are the 3 different parts connected to the bottom of the eye piece?

Answer 11

The objectives

Question 12

What equipment would you need when drawing a labelled diagram of a plant cell?

Answer 12

• Pencil
• Ruler
• Rubber
• Unlined paper
• Light microscope

Question 13

What is the method for drawing a labelled diagram of a cell?

Answer 13

• Focus the microscope on a single cell
• Draw details of the parts of the cell that are important to your study
• Keep looking back at the cell as you draw, draw only what you see, not what you’re meant to see

Question 14

What is the method used to investigate the effect of pH on enzymes (using starch and amylase)?

Answer 14

• Add amylase to buffered starch solution in a test tube
• Place the test tube in a water beaker that is being heated by a bunsen burner at a constant temp
• Take samples of the mixture every 10 seconds and mix them with a fresh drop of iodine solution on a dimple tile
• Repeat until the iodine stops changing colour, record the time taken for this to happen
• Repeat the procedure at different pH values

Question 15

What is the method used to identify starch?

Answer 15

Add a few drops of iodine solution to solid food or mix with a solution of the food the iodine/solution will turn blue/black

Question 16

What is the method for identifying reducing sugar?

Answer 16

Add a few drops of Benedict’s solution to a food solution and mix, heat the solution in a water bath at around 95 degrees for a few minutes, the solution should turn green, orange or red depending on how much sugar is present

Question 17

What is the method for identifying proteins? (biuret test)

Answer 17

Add a few drops of 0.1 moldm^-3 potassium hydroxide solution to the food solution and mix, then add a few drops of 0.01moldm^-3 copper sulfate solution and mix, the solution should turn pale purple if protein is present

Question 18

What is the method used to identify fats?

Answer 18

Add a few drops of ethanol to the food solution and shake thoroughly, add water to the mixture

Question 19

What is the method for finding the energy in a sample of food? (calorimetry)

Answer 19

• The temperature of the water at the start is taken
• The mass of the food sample is measured
• The food is set alight using a bunsen burner and immediately placed under the tube containing the water
• The temperature of the water is taken when the food has stopped burning and the temperature change is calculated

Question 20

What is the method for investigating osmosis in potatoes?

Answer 20

• Mark the value of one solution concentration on one test tube, repeat for each different concentration of solution
• Fill each tube around 2/3 full with the appropriate solution
• Blot a piece of potato dry on a paper towel then measure and record its mass, then use forceps to place it into one of the tube, repeat this for all tubes
• After 20 minutes remove each piece of potato and blot it dry on a paper towel
• Measure each piece of potato’s mass and calculate the percentage change in mass

Question 21

What is a solute?

Answer 21

The substance dissolved by the solvent

Question 22

What is a solvent?

Answer 22

A substance able to dissolve other substances

Question 23

What is a solution?

Answer 23

A liquid mixture containing a solvent and a solute, the solute has been dissolved by the solvent

Question 24

How do you calculate percentage change in mass?

Answer 24

((Final mass - initial mass) / initial mass ) x 100

Question 25

How is DNA extracted from fruit?

Answer 25

• First the fruit is grinded with sand using a pestle and mortar
• Then detergent is added to break down cell membranes, this enables the DNA to be taken out of the cell
• Finally ice cold ethanol is added so the DNA precipitates, this puts the DNA all in one place so it has then been extracted from the fruit

Question 26

What is the method for investigating microbial cultures?

Answer 26

• First turn the bacterial plate upside down and mark the base into 3 sections (one for each test disc), label each section with the substance used
• Turn the plate the right way up and open the lid just enough so that the discs can be placed on the bacterial lawn
• Use the sterile forceps to place each disc in its designated section, make sure you sterilise the forceps between placing each disc on the lawn by heating them with a blue flame on a bunsen burner
• Tape the lid to the base of the plate without completely sealing it to avoid the risk of harmful anaerobic bacteria growing inside
• Incubate the plate for a few days at 25 degrees
• Accurately measure the diameter of any clear area in mm, the larger the diameter of a clear area around the disc, the more effective the substance is at killing bacteria