1.2 Ultrastructure of cells

Question 1

What do prokaryotes lack?

Answer 1

• A nucleus
• Membrane bound organelles

Question 2

Examples of prokaryotes:

Answer 2

• Bacteria
• Archaea
  (unicellular organisms)

Question 3

Cell wall

Answer 3

• In prokaryotes and eukaryotes (only in plant cells)
• Encloses the cell, protecting it and helping to maintain its shape
• Prevents the cell from bursting in hypotonic media

Question 4

Plasma membrane

Answer 4

• In prokaryotes and eukaryotes
• Controls the movement of substances in and out of the cell

Question 5

Cytoplasm

Answer 5

• In prokaryotes and eukaryotes
• Medium that fills the cell
• Is site of all metabolic reactions
• In eukaryotes: holds all organelles and contains enzymes that catalyse various reactions e.g. glycolysis

Question 6

Pili (singular: pilus)

Answer 6

• Only in prokaryotes
• Protein filaments on the cell wall
• Help in cell adhesion and in transferring of DNA between two cells: joining bacterial cells in preparation for transfer of DNA from one cell to another

Question 7

Flagella (singular: flagellum)

Answer 7

• Only in prokaryotes
• Much longer than pili
• Responsible for locomotion of organism
• Their whip-like movement propels the cell along

Question 8

70s ribosomes

Answer 8

• Only in prokaryotes
• Sites of protein synthesis

Question 9

80s ribosomes

Answer 9

• Only in eukaryotes
• Sites of protein synthesis
• Free ribosomes produce proteins used inside the cell itself

Question 10

Nucleoid region

Answer 10

• Only in prokaryotes
• Includes naked (circular) DNA
• Controls all the activities of the cell as well as the reproduction of the organism

Question 11

Plasmids

Answer 11

• Only in prokaryotes
• Small circles of DNA that carry a few genes
• These often give the cell antibiotic resistance
• Used in creating genetically modified bacteria

Question 12

Nucleus

Answer 12

• Only in eukaryotes
• Contains genetic material – DNA – which is stored
  as chromosomes
• Separated from cytoplasm by a double nuclear
  membrane (nuclear envelope)
• Controls all the activities of the cell as well as the reproduction of unicellular organisms

Question 13

Nucleolus

Answer 13

• Only in eukaryotes
• Part of the nucleus that is involved in the production of ribosomes

Question 14

Smooth endoplasmic reticulum

Answer 14

• Only in eukaryotes
• Responsible for producing and storing lipids, involving steroids

Question 15

Rough endoplasmic reticulum

Answer 15

• Only in eukaryotes
• Transports the protein produced by the ribosomes of its surface to the Golgi apparatus
• These proteins are usually for the outside of the cell

Question 16

Golgi apparatus

Answer 16

• Only in eukaryotes
• Processes and packages proteins which are ultimately released in Golgi vesicles

Question 17

Vesicle

Answer 17

• Only in eukaryotes
• A small sac that transports and releases substances produced by the cell by fusing with the cell membrane

Question 18

Lysosomes

Answer 18

• Only in eukaryotes
• Only in animal cells
• Contain hydrolytic enzymes
• Play important role in the destruction of microbes engulfed by white blood cells, as well as the destruction of old cellular organelles

Question 19

Centrioles

Answer 19

• Only in eukaryotes
• Only in animal cells
• Plays an important role in the process of nuclear division by helping to establish the microtubules

Question 20

Vacuole

Answer 20

• Only in eukaryotes
• Generally only in plants
• Helps in the osmotic balance of the cell and in the storage of substances

Question 21

Chloroplast

Answer 21

• Only in eukaryotes
• Only in plant cells
• Double-membrane-bound organelles
• They contain pigments, mainly chlorophyll
• Responsible for photosynthesis

Question 22

Binary fission
(asexual reproduction in prokayrotes)

Answer 22

Prokaryotes reproduce by binary fission to produce two genetically identical cells.
- The chromosome is replicated semi-conservatively, beginning at the point of origin.
- Beginning with the point of origin, the two copies of DNA move to opposite ends of the cell.
- The cell elongates (grows longer).
- The plasma membrane grows inward and pinches off to form two separate, genetically identical cells.

Question 23

Compartmentalisation - eukaryotes

Answer 23

The formation of compartments within the cell by membrane-bound organelles.
Example: the inside of the mitochondrion is completely sealed from the cytoplasm by the mitochondrial envelope, allowing it to carry out reactions without being affected by other reactions occurring in the cell

Question 24

Exocrine gland cell

Answer 24

• An exocrine gland secretes enzymes into a duct.
• Example: exocrine cell from pancreas –> secretes digestive enzymes via the pancreatic duct into the small intestine, where they aid the digestion of food
• They have a well developed network of rough endoplasmic reticulum for protein synthesis (since enzymes are proteins)
• As well as Golgi apparatus that produce the vesicles containing these enzymes

Question 25

Palisade mesophyll cells

Answer 25

• Main function of these cells: to photosynthesize; producing complex organic compounds
• Contains many chloroplasts: the palisade mesophyll tissue contains the greatest number of chloroplasts per cell in plants
• Positioned right under the upper epidermis where it is exposed to the highest amount of light

Question 26

Electron microscopes vs light microscopes

Answer 26

Electron microscopes have a much higher resolution and higher range of magnification than light microscopes
Electron microscopes –> can be used to observe non-living/dead specimens in black and white
Light microscopes –> can be used to observe living specimens in color

Question 27

Mitochondria

Answer 27

• Site of aerobic respiration (to produce ATP)
• Double membrane structure, inner membrane highly folded into internal cristae which increase the surface area for the attachment of the molecules which are
  associated with aerobic respiration.