AQA A Level Chemistry: Methods of Studying Cells

Question 1

What are the three main types of microscopes used to study cells?

Answer 1

1. Light microscope
   
   2. Transmission electron microscope (TEM)
   3. Scanning electron microscope (SEM)

Question 2

What is magnification?

Answer 2

magnification= size of image/ actual size of object

Question 3

What is resolution?

Answer 3

The ability to distinguish two objects as separate entities; higher resolution gives a clearer and more detailed image.

Question 4

What is the maximum magnification and resolution of a light microscope?

Answer 4

• Magnification: x1500
  
  • Resolution: 200 nm

Question 5

How does a transmission electron microscope (TEM) work?

Answer 5

• Passes a beam of electrons through a thin specimen.
  
  • Denser areas absorb more electrons, appearing darker.
  • Produces 2D images with very high resolution.

Question 6

What is the maximum magnification and resolution of a TEM?

Answer 6

• Magnification: x1,000,000
  
  • Resolution: 0.1 nm

Question 7

How does a scanning electron microscope (SEM) work?

Answer 7

• Beams electrons across the surface of the specimen.
  
  • Reflected electrons create a 3D image of the surface.

Question 8

What is the maximum magnification and resolution of a SEM?

Answer 8

• Magnification: x500,000
  
  • Resolution: 1–20 nm

Question 9

What are the advantages of using a light microscope?

Answer 9

• Can observe living cells.
  
  • Easy to use and prepare slides.
  • Produces colour images.

Question 10

What are the limitations of a light microscope?

Answer 10

• Low resolution and magnification.
  
  • Cannot see internal organelles in detail.

Question 11

What are the advantages of a TEM?

Answer 11

• High resolution shows detailed internal structures.
  
  • Can see organelles like ribosomes and membranes.

Question 12

What are the limitations of a TEM?

Answer 12

• Only produces 2D images.
  
  • Requires thin specimens.
  • Can only view dead specimens due to vacuum.

Question 13

What are the advantages of a SEM?

Answer 13

• Produces detailed 3D images of the surface.
  
  • Good for studying external structures.

Question 14

What are the limitations of a SEM?

Answer 14

• Lower resolution than TEM.
  
  • Can only view dead specimens.

Question 15

What is cell fractionation?

Answer 15

A process used to separate organelles from cells to study their structure and function.

Question 16

What are the three main steps of cell fractionation?

Answer 16

1. Homogenisation – Breaking cells open using a blender.
   
   2. Filtration – Removing debris and whole cells.
   3. Ultracentrifugation – Spinning at high speeds to separate organelles by density.

Question 17

What are the conditions for cell fractionation?

Answer 17

• Cold: Reduces enzyme activity.
  
  • Isotonic: Prevents osmosis and organelle damage.
  • Buffered: Maintains pH to avoid denaturing enzymes.

Question 18

What is the order of organelles separated by ultracentrifugation?

Answer 18

1. Nucleus (heaviest)
   
   2. Chloroplasts (in plant cells)
   3. Mitochondria
   4. Lysosomes
   5. Endoplasmic reticulum
   6. Ribosomes (lightest)

Question 19

What is the pellet and supernatant in ultracentrifugation?

Answer 19

• Pellet: Contains the denser organelles that settle at the bottom.
  
  • Supernatant: The liquid above containing lighter organelles.

Question 20

What is artefact formation in electron microscopy?

Answer 20

Structures that appear due to sample preparation, not actually part of the specimen.