Required Practicals Flashcards
Preparing Slides:
When do you add iodine or methylene blue?
Iodine - Plant (onion cell)
Methylene Blue - Animal (cheek cell)
Why is iodine or methylene blue added?
So that the cells in the plant (onion) and animal (cheek) cells can be clearly seen.
Using a ………………………, slowly lower a …………….. over it.
Using a mounted needle, slowly lower a coverslip over it.
Culturing Microorganisms:
Why must you wash your hands with an antibacterial soap and clean your working area with disinfectant spray?
To kill unwanted bacteria that could contaminate the bacteria that is being grown.
Why is a Bunsen burner used?
Give 2 reasons.
- 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.
- 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.
Why is the Petri dish sealed shut with tape? Give 2 reasons.
- Prevents bacteria leaving or entering the Petri dish.
2. Allows oxygen to enter the Petri dish so that aerobic bacteria can be grown.
Why must the bacteria be incubated at 25 degrees Celsius?
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.
Preventing Bacteria Growth:
Why must each antiseptic be labeled on the Petri dish?
So that after the bacteria has been killed by each antiseptic, we can know which antiseptic is which.
When lifting the lid of the Petri dish to place each disc of antiseptic, why must this be done very quickly?
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.
Area of clear zone?
Using a ruler, measure the diameter of each clear zone. Then calculate the area of each clear zone:
A=PIr2
Effect of pH on Amylase Enzyme:
Why is iodine used?
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
Why are the mixtures placed into a water bath at 25 degrees Celsius?
To ensure that each mixture is the same temperature as temp can affect the amylase enzyme. Control variable.
Why must the pipette be rinsed after each addition of the mixture into each depression of the spotting tile?
To ensure that the previous addition of the mixture has been washed off the pipette so that it does not affect the next addition.
Why must the experiment continue until the amylase/buffer/starch mixture remains orange?
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.
How to calculate the rate of reaction?
1 divided by t.
t= time taken for amylase to break down starch