Microscopy

Question 1

What is microscopy?

Answer 1

Microscopy is the science that studies structure, magnification, lenses and techniques related to the use of microscopes.

Question 2

What is a microscope?

Answer 2

A microscope is an instrument that magnifies images of very tiny objects to show great details.

Question 3

Define ‘magnification’

Answer 3

Magnification is the number of times that an image is larger than the specimen

i.e. The ratio of an object’s image size to its real size

Question 4

What is the formula for magnification?

Answer 4

Magnification = 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑖𝑚𝑎𝑔𝑒 / 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛

Question 5

Give the SI units for the following units of measurement:

1. Angstrom
2. Nanometer
3. Micrometer
4. Milimetre
5. Centimeter

Answer 5

1. Å
2. nm
3. μm
4. mm
5. cm

Question 6

An animal cell of 60μm length is enlarged photographically. An enlargement print is made showing the cell at 12cm.
What is its magnification?

Answer 6

X 2000

1cm = 1x104 μm = 10,000μm
12 cm = 12 X 10,000 = 120,000 μm
Magnification = 120,000/ 60 = X2,000

Question 7

A plant cell is magnified X2000 and the length of the chloroplast in the diagram is 16mm.
Calculate the actual length of the chloroplast in μm

Answer 7

8 μm

1mm = 1 x 103μm = 1,000 μm
16 cm = 16 X 1000 = 16,000 μm

Magnification =size of image / size of specimen
X2000 = 16000 /size of specimen

Actual size of specimen = 16,000 = 8 μm

Question 8

Define resolution

Answer 8

Resolution is a measure of the clarity of the image

The ability of a microscope to show two objects as separate

i.e. the minimum distance two points can be separated and still be distinguished as two points.

e.g what appears to the unaided eye as one star in the sky may be resolved as twin stars with a telescope

Question 9

Define ‘limit of resolution of a microscope’

Answer 9

The limit of resolution of a microscope is the minimum distance between two points at which they are still distinguished as two separate points

Question 10

State the two types of microscopes

Answer 10

• Light microscope
• Electron microscope

Question 11

Give the advantages of the light microscope

Answer 11

• It can view live specimens (thus life processes can be observed)
• Natural color of the specimen can be observed
• It is cheap to purchase and operate
• Small and portable
• Unaffected by magnetic fields
• Preparation of material is relatively quick, simple and requires little expertise

Give the disadvantages of the light microscope
- Low resolving power
- Low magnification of 2000x
- Cannot be used in the absence of light

Question 12

What are the advantages of an electron microscope?

Answer 12

• High resolving power
• High magnification of over 500,000x
• Can be used in the absence of light

Question 13

Give the disadvantages of an electron microscope

Answer 13

• Live specimens cannot be viewed thus life processes cannot be studied
• All images are in black and white
• Expensive to purchase and operate
• Very large
• Affected by magnetic fields
• Preparation of material is lengthy
• Preparation of material may distort the specimen

Question 14

What is the radiation source of an electron microscope?

Answer 14

• Electrons

Question 15

What is the radiation source of a light microscope?

Answer 15

• Light

Question 16

Arrange from biggest to smallest;
Nanometer, meter, millimeter, micrometer

Answer 16

Meter> millimeter > micrometer > nanometer

Question 17

What is staining?

Answer 17

This is the application of stain to a sample in order to color cells, tissues, components or metabolic processes for contrast.

Question 18

What is the role of staining samples?

Answer 18

• To enhance visualization of the cell or cellular components under a microscope
• To highlight metabolic processes
• To differentiate between live and dead cells in a sample

Question 19

What is cell fractionation?

Answer 19

This is the technique of isolating cell organelles into fractions so that their functions can be separately studied

Question 20

Which instrument is used for cell fractionation?

Answer 20

Centrifuge

(The process being centrifugation)

Question 21

By centrifugation, give the order of cell components from top to bottom;

Mitochondria, ribosomes, chloroplasts, unbroken cells & cell debris, nuclei, lysosomes

Answer 21

Ribosomes, lysosomes, mitochondria, chloroplasts, nuclei, unbroken cells & debris

Question 22

Which is the lightest cell component?

Answer 22

Ribosomes

Question 23

Which is heavier, chloroplasts or mitochondria?

Answer 23

Chloroplasts

Question 24

What is ultrastructure?

Answer 24

This is an internal detailed structure of a cell as seen by an electron microscope

Question 25

Describe the structure of the animal cell under the light microscope

Answer 25

• Contains protoplasm ( nucleus and cytoplasm) surrounded by a thin plasma membrane.

-Relatively large central nucleus surrounded by the cytoplasm.

-The nucleus contains coiled threads called chromatin.

-Chromatin contains DNA and proteins called histones which together condense to form chromosome during cell division.

-(DNA carries genetic material which controls cell activities and determines the organism’s characteristics.)

-The cytoplasm contains organelles suspended within.

Question 26

Describe the structures of the plant cell as seen by the light microscope

Answer 26

NB: A typical plant cell has additional specialised structures as well as many of those found in an animal cell.

• Protective, rigid, cellulose cell wall surrounding the cell.

-Plant cells have a nucleus and cytoplasm which are usually peripheral.

-The cytoplasm contains chlorophyll pigments which carry out photosynthesis.

-A large central vacuole filled with cell sap is present in mature plant cells.

• The vacuole is surrounded by the tonoplast

Question 27

What is a micrograph?

Answer 27

This is the diagram observed under the electron microscope