Required practicals Flashcards
Describe how temporary mounts of plant tissue are made
Thin section
Put on slide in water/ solution/stain
Add cover slip
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.
Select large number of cells / select cells at random;
Count number of chloroplasts
Divide number of chloroplasts by number of cells
The student cut thin sections of tissue to view with an optical microscope.
Explain why it was important that the sections were thin
Spread out cells
To allow more light through
A single/few layers of cells to be viewed
When the student was making their microscope slides, they were told to ensure they did not move the coverslip sideways. Explain why
To prevent cells from rolling on top of each other/to not damage the chromosomes
Mitosis is important in the life of an organism. Give 2 reasons why
Growth / increase in cell number
Replace cells / repair tissue
Genetically identical cells;
Asexual reproduction / cloning
What is the mitotic index?
Ratio of cells undergoing mitosis to the total number of cells
Why was it important to wash the beetroot discs before the start of the investigation?
To show that any pigment released is from the effect of the alcohol
Why were you instructed to shake the test tubes every minute?
Increase contact of all surfaces with alcohol
Explain why you were instructed to pour the alcohol immediately from the experimental test tube into a clean test tube
So that the pigment could not diffuse out of the discs
Describe a method the student could have used to monitor the temperature of the water in each tube
Use a thermometer to take readings
Explain why it was important that the student put the same volume of water in each tube
If there is less water, then the pigment concentration will be higher
So results (from different temperatures) are comparable
What three environmental variables should be controlled?
CO2 concentration
Light intensity
Temperature
Why was the temperature kept constant?
No denaturation of proteins in enzyme
Why were the discs shaken?
All surfaces of the discs exposed to water
why were the discs cut to the same thickness
same volume: surface area ratio. Controlling over surface area having any effect
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
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
Why is bacteria incubated at 25 degrees Celsius
To prevent the growth of pathogens which occurs at higher temperatures
How can you compare the effectiveness of different antibiotics applied to the same bacteria?
Measure the diameter and calculate the area of the zone of inhibition
