4. Cell Structure

Question 1

What is an optical microscope?

Answer 1

Uses light
Lower resolution due to longer wavelength
Only nucleus, cytoplasm and cell walls can be seen
Can view live specimens
Shows colour
Easy prep
Focuses using lenses

Question 2

Whats an electron microscope?

Answer 2

Uses electrons.
Greater resolution due to short wavelength.
Smaller organelles can be seen.
Can only view dead specimens that are thinner than with optical.
No colour.
Require more time consuming, complex prep.
Focuses using magnets.

Question 3

What are the 2 types of electron microscope and how are they different?

Answer 3

Scanning electron microscope:
- 3D
- Lower resolution
- Only surface visible
Transmission electron microscope:
- 2D image
- Higher resolution
- Detailed internal structures visible.

Question 4

What is the main problem with an electron microscope?

Answer 4

Produces artefacts which can take scientist lots of time to be able to distinguish them between cells.

Question 5

What is magnification?

Answer 5

Making an object appearance increase in size.

Question 6

What is resolution?

Answer 6

Ability to distinguish between 2 separate points. Higher resolution, greater the detail.

Question 7

How is small intestine adapted to function?

Answer 7

Folded to make microvilli providing a large SA to maximise absorption.

Question 8

How do prokaryotic cells differ from eukaryotic cells?

Answer 8

• much smaller
• cytoplasm lacks membrane bound organelles
• smaller ribosomes
• no nucleus but have circular DNA molecule that free in cytoplasm
• cell wall which contains murein ( a glycoprotein)
  SOME HAVE: plasmids, flagella, a capsule surrounding the cell.

Question 9

How do prokaryotic cells differ from eukaryotic cells?

Answer 9

• much smaller
• cytoplasm lacks membrane bound organelles
• smaller ribosomes
• no nucleus but have circular DNA molecule that free in cytoplasm
• cell wall which contains murein ( a glycoprotein)
  SOME HAVE: plasmids, flagella, a capsule surrounding the cell.

Question 10

What is the structure of a virus?

Answer 10

Acellular and non living.
Have genetic material ( DNA or RNA), a capsule and attachment proteins embedded in lipid envelope.
If they have RNA genome, may contain enzyme of reverse transcriptase.

Question 11

Why is a virus acceluar?

Answer 11

It requires host cells to replicate.

Question 12

What are the differences between eukaryotic snd prokaryotic?

Answer 12

Eukaryotic has a linear DNA inside the nucleus, prokaryotic have circular DNA found free in the membrane.
Prokaryotic mesospme id site of respiration, eukaryotic mitochondria is site respiration.
P has 70s ribosomes but E had 80s ribosomes
P cell wall made of peptidoglycan but E made of cellulose.
P has no membrane bound organelles but E has many membrane bound organelles.

Question 13

What is ATP and how does it work?

Answer 13

Adenosine triphosphate is a typebof nucleotide made from molecule of ribose, adenine and 3 phosphate groups.
Hydrolysis of ATP into ADP and an inorganic phosphate (Pi) is catalysed by enzyme ATP hydrolase
The Pi can be used to phosphorylate other compounds.
ATP resynthesises by condensation of ATP and Pi , catalysed by the enzyme ATP synthase during respiration.

Question 14

Whats cell fractionation and ultracentrifugation used for?

Answer 14

Separate cell components.

Question 15

Whats the process for cell fractionation?

Answer 15

• homogenise (blend ) to break open the cells
• filter to remove large cell debris
• suspend in ice cold isotonic buffer solution.
• place suspension in a centrifuge.

Question 16

Why is cell fractionation suspended in ice cold isotonic buffer solution?

Answer 16

Ice cold- stops enzyme activity to prevent digestion of organelles.
Isotonic- same water potential as organelles, prevent osmosis so there will be no osmotic lysis of organelles and no shrinkage.
Buffer- maintains pH so that proteins are not denatured

Question 17

Whats the process of ultracentrifugation?

Answer 17

• centrifuge on slow speed
• 1st pellet will contain all nuclei as its the densest organelle.
• remove the supernatant from above pellet.
• centrifuge the supernatant at a faster speed.
• mitochondria ( and chloroplasts) will be found in 2nd pellet as its less dense.
  Repeat if required.

Question 18

How do you obtain temporary mount of plant tissue to observe starch grain using light microscope?

Answer 18

Add drop water to glass slide.
Obtain thin section plant tissue and place on slide
Stainless starch grains blue black with iodine.
Use mounted needle lower cover slip down onto sample avoiding air bubbles.

Question 19

How do you measure a cell?

Answer 19

Using a eyepiece gratitude
Calibrate using stage micrometer ( with known length)
Place specimen on microscope and use gratitude to measure length cell.