Studying Cells

Question 1

What is the function of ribosomes?

Answer 1

Site of protein synthesis

Question 2

What is the function of the nucleus?

Answer 2

• Contains genetic material/DNA

- Controls cell activity

Question 3

What is the function of the mitochondria?

Answer 3

• Site of aerobic respiration

- ATP production

Question 4

What is the function of the smooth endoplasmic reticulum?

Answer 4

Site of lipid synthesis

Question 5

What is the function of the rough endoplasmic reticulum?

Answer 5

• Encrusted in ribosomes
• Site of protein synthesis
• Transports and stores proteins within the cell

Question 6

What is the function of the golgi apparatus?

Answer 6

• Modifies/packages/sorts proteins

- Produces vesicles

Question 7

What is the function of lysosomes?

Answer 7

• Contains digestive enzymes

- Digests worn out organelles/autolysis

Question 8

What is the function of the cell surface membrane?

Answer 8

• Made of a phospholipid bilayer
• Controls what enters the cell / is selectively permeable
• Can be folded to increase surface area

Question 9

What is the function of chloroplasts?

Answer 9

• Contains thylakoids, stacked into granum

- Site of photosynthesis

Question 10

What is the function of a capsule?

Answer 10

• Protects cell from immune systems

- Aids bacteria sticking together

Question 11

What is the function of the plasmid?

Answer 11

• Circular DNA

- Contains antibiotic resistance genes

Question 12

What is the function of the cell wall?

Answer 12

• Provides rigid shape/structure

- Stops osmotic lysis

Question 13

What is the function of the flagellum?

Answer 13

Allows movement/propulsion

Question 14

Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells.

Answer 14

1. DNA in nucleus is code (for protein)
2. Ribosomes/rough endoplasmic reticulum produce protein
3. Mitochondria produce ATP (for protein synthesis)
4. Golgi apparatus package/modify proteins
5. Vesicle transport OR rough endoplasmic reticulum transports
6. Vesicles fuse with cell (surface) membrane

Question 15

Describe the differences between eukaryotic and prokaryotic cells.

Answer 15

Comparisons:
1. Nucleotide structure is identical
2. Nucleotides joined by phosphodiester bond
OR
Deoxyribose joined to phosphate in sugar, phosphate backbone)
3. DNA in mitochondria / chloroplasts same/similar structure as DNA in prokaryotes
Contrasts:
4. Eukaryotic DNA is longer
5. Eukaryotic DNA contain introns, prokaryotic DNA does not
6. Eukaryotic DNA is linear, prokaryotic DNA is circular
7. Eukaryotic DNA is associated with histones, prokaryotic DNA is not

Question 16

State three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

Answer 16

Plant v prokaryote

1. Associated with histones v no histones
2. Linear v circular
3. No plasmids v plasmids
4. Introns v no introns
5. Longer v shorter

Question 17

The structure of a cholera bacterium is different from the structure of an epithelial cell from the small intestine. Describe how the structure of a cholera bacterium is different.

Answer 17

1. Cholera bacterium is prokaryote
2. Does not have a nucleus/nuclear envelope/has DNA free in cytoplasm
   3 and 4. Any two from: No membrane-bound organelles/no mitochondria/no golgi/no endoplasmic reticulum
   5 Small ribosomes only
   6 and 7. Any two from Capsule/flagellum/plasmid / cell wall

Question 18

Give one advantage of using a TEM rather than a SEM.

Answer 18

1. Higher resolution
2. Higher maximum magnification/higher detail
   OR
3. Allows internal structures within cells to be seen/cross section to be taken

Question 19

Give one advantage of using a SEM rather than a TEM.

Answer 19

Thin sections do not need to be prepared/shows surface of specimen/can have 3D images

Question 20

Scientists use optical microscopes and transmission electron microscopes to investigate cell structure. Explain the advantages and limitations of using a TEM to investigate cell structure.

Answer 20

Advantages:
1. Small objects can be seen
2. TEM has high resolution;
3. Electron wavelength is shorter
Limitations:
4. Cannot look at living cells
5. Must be in a vacuum
6. Must cut section/thin specimen
7. Preparation may create artefact

Question 21

Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold, buffered isotonic solution. Explain why the solution was:

a) Isotonic
b) Ice-cold
c) Buffered

Answer 21

a) Prevents osmosis/no (net) movement of water So organelles do not burst/shrivel
b) Reduce/prevent enzyme activity so organelles are not digested/damaged;
c) Maintain a constant pH so proteins do not denature

Question 22

Describe and explain how cell fractionation and centrifugation can be used to isolate mitochondria from a suspension of animal cells.

Answer 22

1. Cell homogenisation to break open cells and release organelles
2. Filter to remove (large) debris/whole cells
3. Use isotonic solution to prevent osmotic damage to mitochondria/organelles
4. Keep cold to prevent/reduce damage to organelles by enzyme
5. Use buffer to maintain pH and prevent protein/enzyme denaturation
6. Use differential centrifuge (at high speed/1000 g) to separate nuclei/cell fragments/heavy organelles;
7. Re-spin (supernatant/after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom
8. Observe pellet with a microscope to identify mitochondria

Question 23

Describe the structure of a phospholipid molecule and explain how phospholipids are arranged in a plasma membrane. (3)

Answer 23

1. Glycerol joined to two fatty acid tails, phosphate group joined to glycerol on opposite side. (joined by condensation reaction with ester bond)
2. Phospholipid has hydrophilic head (phosphate and glycerol) and hydrophobic tails (fatty acid chains)
3. Arrange to form a phospholipid bilayer (Hydrophilic head facing out. Hydrophobic fatty acid chains facing in)