Biology Paper 1 - Required Practical - Light Microscopes

Question 1

Magnification

Answer 1

How many times larger the Image is than the Object

Magnification = Image Size / Actual Size

Determined by objective lens and eyepiece lens

Question 2

Field Of View

Answer 2

When you look through a microscope it is called the FOV
Larger FOV = objective lens with smaller magnification (Power)
Smaller FOV = objective lens with higher magnification since cells appear larger.

Question 3

Focus

Answer 3

All knobs are associated with focusing.

Easier to focus the object using a lower magnification lens.

Question 4

Preparing The Sample

Answer 4

• Make sure the sample is thin - To only have a few layers of cells and to ensure that light passes through.
• Add a stain to sample (usually Iodine) - To make organelles more visible
• Add glass coverslip - Flatten the sample so it remains in focus, and to protect the objective lens.

Question 5

Issues With Preparing The Sample

Answer 5

Glass Coverslip : Might form air bubbles, inhibiting the view. Can be avoided when the glass cover slip is placed using a mounted needle - applying pressure to glass coverslip to remove excess bubbles.

Leakage in the stain applied to sample : Any excess stain can be wiped away using tissue, and avoid using too much stain (only one drop)

Question 6

Electron Microscopes

Answer 6

• Can look at sub-cellular structures and organelles (chromosomes)
• Organism dead due to complex preparation because it requires a vacuum.
• High resolution (0.2 - 10nm) resulting in higher magnification.
• Images in 3D if you are using a scanning electron microscope.
• Image in 2D if you are using a transmission electron microscope.

Question 7

Light Microscopes

Answer 7

• Looking at cell - detail is low (only nucleus can be seen)
• Organism can be living.
• Low resolution (200nm) resulting in lower magnification.
• Image is in 2D.