Practicals paper 1

Question 1

how do you use an optical ( light ) microscope to view a prepared slide

Answer 1

1. place the slide onto the stage and use the clips to hold the slide in place
2. select the lowest power objective lens ( usually 4x )
3. position the objective lens so it almost touches the microscope slide. ( to do that slowly turn the coarse focusing dial )
4. IMPORTANT that you look at microscope from side while adjusting the position of objective lens (otherwise there is a risk if looking through eyepiece that the slide becomes damaged)
5. when objective lens almost touches the slide stop turning the dial
6. now look down through eyepiece
7. slowly turn the coarse focusing dial ( this increases the distance between the objective lens and slide - do this till cells come into focus )
8. at this stage use the fine focusing dial to bring the cells to clear focus
9. calculate the total magnification
10. you can select a higher power objective lens from 4x to 10x ( to do this adjust the fine focusing dial to bring the cells back into focus
11. use a pencil to make a clear , labelled drawing of some of the cells and include the magnification scale ( to do this place a clear plastic ruler over the stage and meaure the diameter of the field of view IN MM

Question 2

how do you calculate the total magnification

Answer 2

magnification of eyepiece lens x magnification of objective lens

Question 3

describe how to carry out chemical tests for carbohydrates, proteins and lipids

Answer 3

equipment for IODINE for starch :
- food sample
- test tube
- iodine solution (0.01 mol/dm^3)
pipettes

method
1. put some of the food sample into a test tube
2. add a few drops of iodine solution to the food sample using a pipette
3. if starch is present the solution turns from brown to blue/black

Benedicts test for reducing sugars
equipment:
- food samples
- test tube
- benedicts solution
-hot water bath
-thermometer
-pipettes
METHOD
1. add an equal volume or excess of benedicts solution to the food sample in a test tube
2. place in a hot water bath for a few minutes
3. if reducing sugar is present a brick red precipitate is formed BUT if reducing sugar is absent the solution remains blue
TEST FOR PROTEIN
equipment:
- test tube
- 10cm^3 measuring cylinder
- buiret solution
METHOD