Cell Structure and Specilisation

Question 1

What are the 3 key structural features of a cell

Answer 1

• Exterior plasma membrane. Phospholipid bilayer separates the cell from the external medium.
• Contains nuclear region with DNA as genetic material.
• Interior cytoplasm, a semifluid matrix with remaining cell contents.

Question 2

What are the two main cell types

Answer 2

Eukaryotic
Prokaryotic

Question 3

What is the basic structure of prokaryotic cells

Answer 3

No nucleus, little defined internal structure, and unicellular. Very small, normally 0.5 - 2.0 µm diameter.

Question 4

What is the basic structure of Eukaryotic cells

Answer 4

contain nuclei, more complex structure with specialised organs (organelles),
may be unicellular (yeasts/protozoa) or multicellular (animals, plants, fungi).
Variable size: 2.0 µm upwards, typically 5-20 µm diameter

Question 5

What is the issue with the term prokaryote

Answer 5

can be seen as an outdated term because it covers two separate groups

Question 6

What is Eubacteria

Answer 6

It is the most commonly encountered prokaryote

Question 7

What are the key features of bacteria

Answer 7

• Plasma membrane (PM) delineates edge of cell cytoplasm.
• Rigid cell wall composed of peptidoglycan (carbohydrate/protein polymer) external to the PM. Two classes of bacteria can be recognised depending on their reaction with ‘Gram stain’. Gram positive have only an outer cell wall. Whereas Gram negative have an extra outer membrane external to the cell wall, inbetween lies the ‘periplasmic’ space.
• Relatively simple internal organisation, lacks differentation.
• The genomic DNA present in ‘nucleoid’ region, not separated from surrounding cytoplasm.
• nucleoid DNA in the cytoplasm in a localised area

Question 8

List some ways bacteria cells can differentiate from another

Answer 8

• Cell shape. Round, oval, spiral, curved, rods, chains etc
• Cell appendages. Some have rotating flagella on surface for motility. Many Gram-negative have short ‘fimbriae’ for attachment to surfaces and ‘pili’ for attachment to bacteria
• Some have infoldings of the plasma membrane to allow photosynthesis e.g. the Cyanobacteria (blue green) with apparent internal membranes

Question 9

What other group comes under the term Prokaryote

Answer 9

Archaea

Question 10

How are Archaea similar to Bacteria

Answer 10

size range, shape (rods, round), external flagella and pili. DNA present in nucleoid region, not separate from cytoplasm.

Question 11

How are Archaea different from Bacteria

Answer 11

• But some unique cell shapes – branched, flat, square.
• Have distinct cell biochemistry including cell membranes, DNA molecular differences.
• Lack peptidoglycan cell wall – instead very diverse outer surface layers.
• Found in hostile environments e.g. hot volcanic springs, airless marine sediments, salt lakes. Conditions where primitive life evolved

Question 12

Are Eukaryotes structurally more or less complex than prokaryotic cells?

Answer 12

More complex

Question 13

Describe the main structural features of Eukaryotic cells

Answer 13

• plasma membrane (PM) delineates edge of cell cytoplasm.
• DNA is contained in a nucleus separated from cytoplasm by membrane, DNA present on chromosomes.
• Cytoplasm is compartmentalised. Features series of ‘organelles’ membrane-bound structures with diverse functions.
• Complex cytoskeletal system to maintain cell integrity. Bacteria may have one put not as pronounced
  e.g. microtubules and intermediate and actin filaments

Question 14

In Animal, plant, protist, fungal cells, the main constituents include

Answer 14

• Nucleus
• Organelles: mitochondria, Golgi body, peroxisomes, rough and smooth endoplasmic reticulum, small vacuole - -
• Ribosomes
• CENTRIOLES - on in animal cells
• Cytoskeleton

Question 15

What are the main constituents of plants cells

Answer 15

• Nucleus
  
  • Organelles: mitochondria, Golgi body, peroxisomes, rough and smooth endoplasmic reticulum, and CHLOROPLAST involved with photosynthesis
  • Ribosomes
  • Cytoskeleton
  • SINGLE LARGE VACUOLE
  • RIGID CELLULOSE CELL WALL

Question 16

Main components of Protist cells

Answer 16

• Mainly unicellular
• Flexible cell surface with supportive ‘pellicle’
• Some have contractive vacuole

Question 17

Main components of Fungal cells

Answer 17

• Unicellular yeasts or filamentous hyphae
• Can contain multiple nuclei per compartment
• Rigid chitin cell wall

Question 18

In what organisms has specialisation occurred the most

Answer 18

Multicellular organisms
One of the biggest advances in evolution of life

Question 19

Multicellularity also allows what?

Answer 19

Specialisation
Cells have different functions within whole organisms

Question 20

Why do cells differentiate

Answer 20

Cells differentiate as a result of the expression of subsets of genes within the genome

Question 21

Give an example of how a cell can be specialised for movement

Answer 21

Some cells have external projections from cell surface which undulate to cause movement e.g. ‘flagella’ (few and large) or ‘cilia’ (small and numerous). Found in unicellular protists/fungi for propulsion and vertebrate tissues including airways and ears.

Question 22

Give an example of how a cell is specialised for signaling

Answer 22

Nerve cells (neurons) have a central cell body with terminal dendrites, and long axon transmitting electrical signals. Length may be > 1 metre !

Question 23

Give an example of how a cell is specialised for transport

Answer 23

Red blood cells (erythrocytes) specialized for gas transport; lack nucleus and organelles when mature and instead packed full of haemoglobin. Are small (8 µm) for passage through capillaries

Question 24

Give an example of how a cell is specialised for reproduction

Answer 24

Sperm cells have a flagellum for swimming. Mushroom spores are produced on gills by specialized ‘basidia’ swollen reproductive cells.