Studying cells

Question 1

Formula

Answer 1

Image size = actual size x magnification

Question 2

Difference between magnification and resolution?

Answer 2

Magnification is how much bigger the image size is then the actual image (specimen) whereas resolution is the minimum distance where two very close objects can be distinguished

Question 3

Conversion?

Answer 3

1 mm = 1000 micrometre. 1 mm = 1,000,000 nanometre

Question 4

Which type of microscope has the highest resolution?

Answer 4

TEM > SEM > LM

Question 5

Why do electron microscopes have a higher resolution?

Answer 5

Electron microscope uses electrons which have a shorter wavelength (light microscope uses light which has a large wavelength)

Question 6

How does a transmission electron microscope work?

Answer 6

Uses a beam of electrons which pass through the specimen. Denser parts absorb more electrons so appear darker.

Question 7

How does a scanning electron microscope work?

Answer 7

Electrons bounce of the specimens surface

Question 8

Advantages and disadvantages of transmission electron microscope?

Answer 8

Advantages

• highest magnification and resolution
• can see internal structures of organelles

Disadvantages

• works in a vacuum so can only use dead specimen
• specimen needs to be thin
• black and white image produced
• 2d image
• artefacts

Question 9

Advantages and disadvantages of scanning electron microscope?

Answer 9

Advantages

• produces 3d images
• can be used on thick specimen

Disadvantages

• black and white images produced
• works in a vacuum so can only use a dead specimen
• artefacts
• lower resolution and magnification than TEM

Question 10

What is an artefact?

Answer 10

Things you can see down the microscope that aren’t part of the specimen or cell

Question 11

Why can organelles appear different in images?

Answer 11

viewed from different angles and at different levels/depth

Question 12

How do you separate cell components?

Answer 12

cell fractionation and ultracentrifugation

Question 13

Cell Fractionation?

Answer 13

• Breakdown tissue into cells (cut, pestle & mortar)
• add cold/isotonic/buffer solution (cold = reduce enzyme activity, isotonic = same water potential so organelle does not shrink or burst, buffer = maintains constant pH)
• homogenate – breaks open cells releasing organelles
• filter = removes large debris and intact cells
• centrifuge – spin at low speed, largest organelle builds at bottom (nucleus), leaves supernatant, spin at higher speed, next heaviest organelle forms at bottom (chloroplast or mitochondria)
• (organelle by size: nucleus, chloroplast, mitochondria, endoplasmic reticulum/golgi body/lysosomes, ribosomes)