Cell Structure

Question 1

Outline how a student could prepare a temporary mount of tissue for a light microscope.

Answer 1

1. Obtain thin section of tissue e.g. using ultra tome or by maceration
2. Place plant tissue in a drop of water
3. Stain tissue on a slide to make structures visible
4. Add coverslip using mounted needle at 45 degrees to avoid trapping air bubbles

Question 2

Describe how light microscopes work

Answer 2

1. lenses focus rays of light and magnify the view of a thin slice of specimen
2. Different structures absorb different amounts and wavelengths of light
3. Reflected light is transmitted to the observer via the objective lens and eyepiece

Question 3

Describe how a transmission electron microscope (TEM) works

Answer 3

1. Pass a high energy beam of electrons through a thin slice of specimen
2. More dense structures appear darker since they absorb more electrons
3. Focus image onto fluorescent screen or photographic plate using magnetic lenses

Question 4

Describe how a scanning electron microscope (SEM) works

Answer 4

1.Focus a beam of electrons onto a specimen’s surface using electromagnetic lenses
2. Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate

Question 5

Describe how a laser scanning confocal microscope works

Answer 5

1. Focus a laser beam onto a small area on a sample’s surface using objective lenses
2. Fluorophores in the sample emit photons
3. Photomultiplier tube amplifies the signal onto a detector. An image is produced pixel by pixel in the correct order

Question 6

How should the field of view in microscopy be recorded?

Answer 6

Draw a diagram with a sharp pencil. Do not use sketchy lines or shading. Include a scale bar. Annotate visible structures.

Question 7

State an equation to calculate the actual size of a structure from microscopy

Answer 7

actual size = image size / magnification

Question 8

Define magnification and resolution

Answer 8

Magnification: factor by which the image is larger than the actual specimen
Resolution: smallest separation distance at which 2 separate structures can be distinguished from one another

Question 9

Why do samples need to be stained for light microscopes?

Answer 9

Coloured dye binds to he structures. Facilitates absorption of wavelengths of light produce image. Differential staining: contrast between heavily & lightly stained areas distinguishes structures.

Question 10

What is a microscope?

Answer 10

An instrument which enables you to magnify an object.

Question 11

What was the first microscope to be discovered and when?

Answer 11

Light microscopes in the 16th - 17th century.

Question 12

What happened in the mid-19th century to microscopes?

Answer 12

They had a high enough level of magnification to allow scientiststo see individual cells.

Question 13

What does cell theory state?

Answer 13

• Both plant and animal tissue is composed of cells
• Cells are the basic unit of all life
• Cells only develop from exissting cells

Question 14

Why is light microscopy still important?

Answer 14

• It is easily available
• It is relatively cheap
• It can be used in the field
• It can be used to observe living specimens not just dead, prepared slides

Question 15

When was the first cell observed?

Answer 15

1665 by Robert Hooke

Question 16

When were the first living cells observed?

Answer 16

1674-1683 by Anton van Leeuwenhoek

Question 17

When was evidence for the origin of new plant cells discovered (cell division)?

Answer 17

1832 by Barthélemy Dumortier

Question 18

When was the nucleus first observed?

Answer 18

1833 by Robert Brown

Question 19

When was the birth of a universal cell theory?

Answer 19

1837 - 1838 by (Matthias Schleiden, Jan Purkyné) Theodor Schwann

Question 20

When was evidence for the origin of new animal cells discovered?

Answer 20

1844 (1855) by Robert Remark (who wasn’t believed, theory republished by Rudolf Vinchow as his work)