A level Biology : Module 1 - Microscopes, Resolution and Magnification

Question 1

What is an Electron Micrograph?

Answer 1

Photo of an image seen under an electron microscope

Question 2

What is Magnification?

Answer 2

Number of times larger an image appears compared to the actual size of the object

Question 3

What are Organelles?

Answer 3

Small structures within cells, each one having a particular function

Question 4

What is a photomicrograph?

Answer 4

Photo of an image seen under an optical microscope (light microscope)

Question 5

What is resolution?

Answer 5

The ability to distinguish between 2 points on an image, i.e. the Detail, clarity and clearness of the image

Question 6

Advantages of Light Microscopes

Answer 6

• Cheap
• Relatively easy to use
• Portable, able to use in the field and in labs
• Can be used to study whole living specimens

Question 7

Disadvantages of Light Microscopes

Answer 7

• Resolution is limited, so we cannot magnify any higher whilst giving a clear image
• MAX magnification of 1500
• Preparation could distort specimen

Question 8

Information about Electron Microscopes

Answer 8

• Use electrons to form an image
• Higher resolution than light microscope
• Beam of electrons has a far smaller wavelength than light, so can resolve (distinguish between) two objects extremely close together
• Max resolution of around 0.2nm
• 1,500,000 max useful magnification
• Can observe the smaller organelles (ribosomes, ER, lysosomes)
• 2 types (Transmission and Scanning)

Question 9

Advantages of TEMs

Answer 9

• Produce a high resolution image
• Allows internal structures within cells and organelles to be seen

Question 10

Disadvantages of TEMs

Answer 10

• Can only be used with very thin specimens or thin sections of the object being observed
• Can’t observe live specimens (vaccum, water is removed from specimen)
• Lengthy treatment required to prepare specimens (so artefacts can be introduced, which are the result of preserving and staining and not the actual structures)
• No colour image produced

Question 11

How does a scanning electron microscope work

Answer 11

• Scan a beam of electrons across the specimen
• Beams bounce off the surface and electrons are detected which forms a 3D image of the surface of a specimen

Question 12

Advantages of a Scanning electron microscope

Answer 12

• Can be used on thick or 3D specimens to be observed
• Can observe surface structure in 3D

Question 13

Disadvantages of Scanning Electron Microscopes

Answer 13

• Give lower resolution images (than TEMs)
• Cannot observe live specimens
• No colour images

Question 14

How do Laser Scanning Confocal Microscopes work?

Answer 14

• Relatively new technology
• Cells viewed should be stained with florescent dyes
• Thick section of tissue or small living organism is scanned with a laser beam
• beam reflected by fluorescent dyes
• Multiple depths of the tissue section / organism is scanned producing an image

Question 15

Advantages of Laser Scanning Microcopes

Answer 15

• Used on thick or 3D specimens
• Allow external 3D structures of specimens to be observed
• Clear images produced
• STRUCTURE OF CYTOSKELETON CAN BE SEEN

Question 16

Disadvantages of using Laser Scanning Microscopes

Answer 16

• Slow process
• Laser can cause photodamage to the cells

Question 17

What limits the resolution of an optical microscope?

Answer 17

The wavelength of light (400nm)

Question 18

How to calibrate microscope

Answer 18

• Place stage micrometer on stage (each unit is 10nm)
• Replace eyepiece on microscope with eyepiece graticule
• Line up eyepiece graticule with stage micrometer

Question 19

Why do we stain in microscopy?

Answer 19

• Tissues / organisms are often transparent
• So coloured dyes absorb colours of light while reflecting others, so structures are visible

Question 20

What common stains are used in light microscopy?

Answer 20

Toluidine blue, Phloroglucinol (red/pink)