2.1 Cell Biology

Question 1

What’s the use of Microscopes?

Answer 1

Microscopes can be used to observe and investigate cell structure

Question 2

Types of Microscopes?

Answer 2

Different types of microscope can be used to study cells at different levels of detail
- Light microscopes
- Electron microscopes

Question 3

What are light microscopes?

Answer 3

Light microscopes use light to form an image
- Maximum resolution is 0.2 micrometres (µm)
- Maximum useful magnification is ×1500
- used to observe larger structures:
= entire cells
= nuclei
= mitochondria and chloroplasts

Question 4

Light Microscopes : Positives

Answer 4

• they are small and relatively cheap
• they can be used to produce colour images
• they allow the observation of living specimens

Question 5

Light Microscope : Negatives

Answer 5

• they’re resolution is lower
• they’re magnification is also lower
• aren’t capable of seeing specific small structure

Question 6

What are Electron Microscopes?

Answer 6

Electron microscopes use electrons to form an image
- Maximum resolution of 0.2 nm
- Maximum magnification from around ×1,000,000 up
Electron microscopes can be used to observe small structures inside cells:
= cell membranes
= ribosomes
- there are two types:
= transmission electron microscopes (TEMs)
= scanning electron microscopes (SEMs)

Question 7

Electron Microscopes : Positives

Answer 7

• produces very high resolution therefore the specimen can be well investigated
• also has a very high magnification to identify certain parts
• images can be artificially coloured during processing
• helps validate studies and has 2 different types

Question 8

Electron Microscope : Negatives

Answer 8

• they are very large and expensive
• specimens must be prepared using a highly complex process
• live specimens cannot be observed
• images are always produced as black and white

Question 9

EM : Transmission Electron Microscopes

Answer 9

• Use electromagnets to transmit a beam of electrons through a specimen; denser parts appear darker on the final image
• TEMs produce images that:
  = are high-resolution
  = allow the internal structures within cells
  = are two-dimensional

Question 10

EM : Scanning Electron Microscope

Answer 10

• pass a beam of electrons across the surface of a specimen and then detect the rate at which the electrons bounce back
• SEMs produce images that:
  = are three-dimensional
  = show the surface of specimens
  = lower maximum resolution than TEMs

Question 11

What’s the Magnification Formula?

Answer 11

Magnification = size of Image ÷ size of Actual object

The magnification formula can be rearranged to allow the calculation of:
- magnification (M)
- size of image (I)
- size of actual size (A)

Question 12

Describe conversion units in Magnification:

Answer 12

Units of measurement relate to each other as follows:
- 1000 nm = 1 µm
- 1000 µm = 1 mm
- 1000 mm = 1 m
- 10 mm = 1 cm

Question 13

What is magnification?

Answer 13

Magnification:
The number of times larger an image is than the actual object

The ability of a microscope to magnify an object depends on the type of microscope, and on the features of the microscope itself

Question 14

What is resolution?

Answer 14

Resolution:
The ability to distinguish separate points on an image as two separate objects

The higher the resolution, the shorter the distance at which the two objects can be clearly distinguished

Question 15

What’s a Eukaryotic cell?

Answer 15

• Eukaryotic cells are larger than other cells
• their DNA is contained in a nucleus
• are complex multicellular organisms containing a range of specialized cells

Question 16

EC : Cell Membrane

Answer 16

• cells are surrounded by a cell surface membrane
• it controls the exchange of materials between the internal cell environment and the external environment; involved in osmosis
• membrane is ‘partially permeable’
• in control of what goes inside and outside of the cell

Question 17

EC : Cell Wall

Answer 17

• found in plant cells but not in animal cells
• cell walls are formed outside of the cell membrane
• provide structural support to the cell
• is thick and also provides protection for the cell

Question 18

EC : Nucleus

Answer 18

• present in all eukaryotic cells
• is relatively large and separated from the cytoplasm by a double membrane
• the nuclear envelope: which has many pores
• nuclear pores: are important channels for allowing mRNA and ribosomes to travel out of the nucleus
• nucleolus: are the sites of ribosome production

Question 19

EC : Mitochondria

Answer 19

• the site of aerobic respiration (the powerhouse of the cell)
• are just visible with a light microscope
• surrounded by double-membrane with the inner membrane