Required practicals

Question 1

Describe how temporary mounts of plant tissue are made

Answer 1

Thin section
Put on slide in water/ solution/stain
Add cover slip

Question 2

Describe how the scientist could have used the temporary mounts of leaves to determine the mean number of chloroplasts in mesophyll cells of a leaf.

Answer 2

Select large number of cells / select cells at random;
Count number of chloroplasts
Divide number of chloroplasts by number of cells

Question 3

The student cut thin sections of tissue to view with an optical microscope.
Explain why it was important that the sections were thin

Answer 3

Spread out cells
To allow more light through
A single/few layers of cells to be viewed

Question 4

When the student was making their microscope slides, they were told to ensure they did not move the coverslip sideways. Explain why

Answer 4

To prevent cells from rolling on top of each other/to not damage the chromosomes

Question 5

Mitosis is important in the life of an organism. Give 2 reasons why

Answer 5

Growth / increase in cell number
Replace cells / repair tissue
Genetically identical cells;
Asexual reproduction / cloning

Question 6

What is the mitotic index?

Answer 6

Ratio of cells undergoing mitosis to the total number of cells

Question 7

Why was it important to wash the beetroot discs before the start of the investigation?

Answer 7

To show that any pigment released is from the effect of the alcohol

Question 8

Why were you instructed to shake the test tubes every minute?

Answer 8

Increase contact of all surfaces with alcohol

Question 9

Explain why you were instructed to pour the alcohol immediately from the experimental test tube into a clean test tube

Answer 9

So that the pigment could not diffuse out of the discs

Question 10

Describe a method the student could have used to monitor the temperature of the water in each tube

Answer 10

Use a thermometer to take readings

Question 11

Explain why it was important that the student put the same volume of water in each tube

Answer 11

If there is less water, then the pigment concentration will be higher
So results (from different temperatures) are comparable

Question 12

What three environmental variables should be controlled?

Answer 12

CO2 concentration
Light intensity
Temperature

Question 13

Why was the temperature kept constant?

Answer 13

No denaturation of proteins in enzyme

Question 14

Why were the discs shaken?

Answer 14

All surfaces of the discs exposed to water

Question 15

why were the discs cut to the same thickness

Answer 15

same volume: surface area ratio. Controlling over surface area having any effect

Question 16

Describe two aseptic techniques you would use when transferring a sample of broth culture (bacteria) on to an agar plate.
Explain why each was important

Answer 16

Keep lid on Petri dish TO prevent unwanted bacteria contaminating the dish
Wear gloves/Wash hands TO prevent contamination of agar with bacteria on hands
Use sterile pipette/Flame the loop / Flame the neck of the container of the culture TO maintain a pure culture of bacteria

Question 17

Why is bacteria incubated at 25 degrees Celsius

Answer 17

To prevent the growth of pathogens which occurs at higher temperatures

Question 18

How can you compare the effectiveness of different antibiotics applied to the same bacteria?

Answer 18

Measure the diameter and calculate the area of the zone of inhibition