Required Practicals

Question 1

Preparing Slides:

When do you add iodine or methylene blue?

Answer 1

Iodine - Plant (onion cell)

Methylene Blue - Animal (cheek cell)

Question 2

Why is iodine or methylene blue added?

Answer 2

So that the cells in the plant (onion) and animal (cheek) cells can be clearly seen.

Question 3

Using a ………………………, slowly lower a …………….. over it.

Answer 3

Using a mounted needle, slowly lower a coverslip over it.

Question 4

Culturing Microorganisms:

Why must you wash your hands with an antibacterial soap and clean your working area with disinfectant spray?

Answer 4

To kill unwanted bacteria that could contaminate the bacteria that is being grown.

Question 5

Why is a Bunsen burner used?

Give 2 reasons.

Answer 5

1. The flame kills unwanted bacteria that may be around it. Therefore if the experiment is carried out near the Bunsen burner, there is less risk of bacteria in the air contaminating the bacteria being grown.
2. The inoculated loop must be passed through the Bunsen burner (until it glows red) to sterilize and kill any unwanted bacteria that may be on it that could contaminate the bacteria being grown.

Question 6

Why is the Petri dish sealed shut with tape? Give 2 reasons.

Answer 6

1. Prevents bacteria leaving or entering the Petri dish.

2. Allows oxygen to enter the Petri dish so that aerobic bacteria can be grown.

Question 7

Why must the bacteria be incubated at 25 degrees Celsius?

Answer 7

It is warm enough for bacteria growth but not so warm that the bacteria is able to grow at a rapid rate. This would be dangerous as the experiment is being done in a school environment with school children.

Question 8

Preventing Bacteria Growth:

Why must each antiseptic be labeled on the Petri dish?

Answer 8

So that after the bacteria has been killed by each antiseptic, we can know which antiseptic is which.

Question 9

When lifting the lid of the Petri dish to place each disc of antiseptic, why must this be done very quickly?

Answer 9

To minimize the bacteria’s exposure time to air, making it less likely for bacteria in the air to contaminate the bacteria in the Petri dish.

Question 10

Area of clear zone?

Answer 10

Using a ruler, measure the diameter of each clear zone. Then calculate the area of each clear zone:

A=PIr2

Question 11

Effect of pH on Amylase Enzyme:

Why is iodine used?

Answer 11

As iodine tests for starch. Therefore if the amylase enzyme is able to break down the starch, then the iodine will undergo a color change:
Orange to Blue Black

Question 12

Why are the mixtures placed into a water bath at 25 degrees Celsius?

Answer 12

To ensure that each mixture is the same temperature as temp can affect the amylase enzyme. Control variable.

Question 13

Why must the pipette be rinsed after each addition of the mixture into each depression of the spotting tile?

Answer 13

To ensure that the previous addition of the mixture has been washed off the pipette so that it does not affect the next addition.

Question 14

Why must the experiment continue until the amylase/buffer/starch mixture remains orange?

Answer 14

As this will mean that the amylase can no longer break down the starch and that the reaction is therefore over as the iodine stops changing color.

Question 15

How to calculate the rate of reaction?

Answer 15

1 divided by t.

t= time taken for amylase to break down starch

Question 16

Effect of Light Intensity on Photosynthesis:

Why is sodium hydrogen carbonate used?

Answer 16

As plants need carbon dioxide to photosynthesise and carbon dioxide is found in sodium hydrogen carbonate.

Question 17

What is the symbol for sodium hydrogen carbonate?

Answer 17

NaHCO3

Question 18

Paper clip?

Answer 18

To weigh the Elodea plant down.

Question 19

Why use Elodea?

Answer 19

As it is an underwater plant which means that we are able to put it into the sodium hydrogen carbonate and count the number of bubbles produced by it as the bubbles can be seen in a liquid.

Question 20

Should you begin with the greatest or smallest distance? Why?

Answer 20

The greatest distance. This is because the light intensity will increase as the distance decreases so the anoint of photosynthesis achieved with the smaller distances will not be affected by the amount of photosynthesis achieved with greater distances.

Question 21

How can this experiment be improved?

Answer 21

1. If the oxygen produced was instead collected and then weighed as counting the bubbles is not very accurate. You can miss bubbles and the size of each bubble varies.
2. If a lux meter (light meter) was used instead of changing the distance between the plant and light source. This would mean that the light intensity would be measured directly and therefore be more accurate.

Question 22

Biochemical Tests:

What does iodine test for?

Color change?

Answer 22

Starch.

Orange to Blue black.

Question 23

What does Benedict’s solution test for?

Color change?

Answer 23

Sugars (glucose).

Blue to Green to Orange to Brick red orange.

Question 24

What does Biuret’s solution test for?

Color change?

Answer 24

Protein.

Blue to Pink to Mauve.
Purple ring to the whole solution purple.

Question 25

What does Ethanol test for?

Color change?

Answer 25

Lipids.

Goes cloudy.

Question 26

What does Sudan III test for?

Color change?

Answer 26

Lipids.

Separation. Top layer of bright red stained oil.