Biology Required Practicals AQA
Content:
Paper 1:
Microscope:
Areas of the Microscope:
Stage:
This is where the slide is placed on the microscope.
Clips:
Clips are on the stage, these are used to hold the slide in place on the stage
Lamp:
The lamp is placed below the stage, Light from the lamp passes through the slide, however this
can vary for some microscopes as they have a mirror in the stage to reflect the light up through
the microscope slide.
Objective Lenses:
Placed above the stage. Most light microscopes have 3 DIFFERENT objective lenses. They
usually have a magnification of 4x, 10x or 40x.
Eyepiece
At the top of the microscope. This is where we look through. The eyepiece has a lens which has
a magnification of 10x.
Coarse Focusing Dial and Fine Focusing Dial:
Discussed further down
How to Prepare a slide:
Plant Cell preparation:
1
, Biology Required Practicals AQA
1. Peel a thin, transparent layer of epidermal cells from the inside of an onion.
2. Place cells on a microscope slide.
3. Add a drop of water or iodine (a chemical stain).
4. Lower a coverslip onto the onion cells using forceps or a mounted needle. This
needs to be done gently to prevent trapping air bubbles.
Animal Cell Preparation:
1. Remove cells from the inside of your cheek using a cotton bud.
2. Smear the cotton bud onto a microscope slide.
3. Add a drop of methylene blue (a chemical stain).
4. Lower a coverslip onto the cheek cells using forceps or a mounted needle. This
needs to be done gently to prevent trapping air bubbles.
How to view a prepared slide on the microscope:
First place the slide on to the stage securing the slide with the clips to keep it in place. Then we
use the lowest objective lens (4x magnification) and position the objective lens so it is almost
touching the microscope slide. We do this by turning the Coarse Focusing dial, whilst doing this
you should always be looking from the side. Once the objective lens is almost touching the slide
you must stop turning the dial. If we look through the eyepiece whilst positioning the objective
lens, you are at risk of damaging the slide. Once the objective lens is positioned we look down
through the eyepiece. Whilst doing this, we need to slowly adjust the coarse focusing dial to
increase the distance between the objective lens and slide, this is to help the microscope focus
the cells. After, you use the fine focusing dial to gain a clearer view of the cells. When done with
the lower objective lens (4x magnification) we can move onto a higher magnification (10x
magnification). Again we will need to adjust the fine focusing dial to bring the cells back into
focus, and possibly use the coarse dial to ensure that the objective lens doesn't mess with the
slide. After each magnification we can make pencil drawings based on what cells we can see.
How to calculate the total magnification:
Total Magnification= magnification of the eyepiece lens x magnification of the objective lens
Eyepiece lens magnification= 10x
Low power objective lens magnification= 4x
10 x 4= 40
Total magnification= 40x
Eyepiece magnification= 10x
Mid power objective lens magnification= 10x
10 x 10= 100
Total Magnification= 100x
Eyepiece magnification= 10x
High Power objective lens magnification= 40x
2
Content:
Paper 1:
Microscope:
Areas of the Microscope:
Stage:
This is where the slide is placed on the microscope.
Clips:
Clips are on the stage, these are used to hold the slide in place on the stage
Lamp:
The lamp is placed below the stage, Light from the lamp passes through the slide, however this
can vary for some microscopes as they have a mirror in the stage to reflect the light up through
the microscope slide.
Objective Lenses:
Placed above the stage. Most light microscopes have 3 DIFFERENT objective lenses. They
usually have a magnification of 4x, 10x or 40x.
Eyepiece
At the top of the microscope. This is where we look through. The eyepiece has a lens which has
a magnification of 10x.
Coarse Focusing Dial and Fine Focusing Dial:
Discussed further down
How to Prepare a slide:
Plant Cell preparation:
1
, Biology Required Practicals AQA
1. Peel a thin, transparent layer of epidermal cells from the inside of an onion.
2. Place cells on a microscope slide.
3. Add a drop of water or iodine (a chemical stain).
4. Lower a coverslip onto the onion cells using forceps or a mounted needle. This
needs to be done gently to prevent trapping air bubbles.
Animal Cell Preparation:
1. Remove cells from the inside of your cheek using a cotton bud.
2. Smear the cotton bud onto a microscope slide.
3. Add a drop of methylene blue (a chemical stain).
4. Lower a coverslip onto the cheek cells using forceps or a mounted needle. This
needs to be done gently to prevent trapping air bubbles.
How to view a prepared slide on the microscope:
First place the slide on to the stage securing the slide with the clips to keep it in place. Then we
use the lowest objective lens (4x magnification) and position the objective lens so it is almost
touching the microscope slide. We do this by turning the Coarse Focusing dial, whilst doing this
you should always be looking from the side. Once the objective lens is almost touching the slide
you must stop turning the dial. If we look through the eyepiece whilst positioning the objective
lens, you are at risk of damaging the slide. Once the objective lens is positioned we look down
through the eyepiece. Whilst doing this, we need to slowly adjust the coarse focusing dial to
increase the distance between the objective lens and slide, this is to help the microscope focus
the cells. After, you use the fine focusing dial to gain a clearer view of the cells. When done with
the lower objective lens (4x magnification) we can move onto a higher magnification (10x
magnification). Again we will need to adjust the fine focusing dial to bring the cells back into
focus, and possibly use the coarse dial to ensure that the objective lens doesn't mess with the
slide. After each magnification we can make pencil drawings based on what cells we can see.
How to calculate the total magnification:
Total Magnification= magnification of the eyepiece lens x magnification of the objective lens
Eyepiece lens magnification= 10x
Low power objective lens magnification= 4x
10 x 4= 40
Total magnification= 40x
Eyepiece magnification= 10x
Mid power objective lens magnification= 10x
10 x 10= 100
Total Magnification= 100x
Eyepiece magnification= 10x
High Power objective lens magnification= 40x
2
