A2.2 Cell Structure

Question 1

Outline cell theory

Answer 1

1. All living things are composed of cells.
2. All cells come from preexisting cells.
3. Cells are the basic unit of life.

Question 2

Features of a prokaryote

Answer 2

• Plasma membrane — regulates what goes in and out of the cell
• Nucleoid — uncompartmentalized DNA not wrapped in a membrane, “naked” (not wrapped around a histone)
• Cytoplasm — site of metabolic reactions
• Ribosomes (70s) — synthesize proteins
• Plasmid — circular DNA
• Cell wall — supports the cell and prevents it from bursting by withstanding turgor pressure
• Pili - adhering to surfaces and harpoons DNA to the environment
• Capsule - prevents dehydration and adheres to surfaces
• Flagellum - locomotion, propels the cell

Question 3

Features of a eukaryote

Answer 3

• Plasma membrane, nucleus, cytoplasm
• Cell wall (cellulose in plants, chitin in fungi) — support the cell from increased or decreased turgor pressure in photosynthetic cells
• Rough ER — most ribosomes are attached here, synthesizing secretory proteins which are then packaged into transport vesicles
• Chloroplast — uses water, CO2 and light energy to produce glucose and oxygen for photosynthesis
• Golgi apparatus — receives transport vesicles and modifies the proteins from the rER. Produces secretory vesicles.
• Vacuole — larger than vesicles, stores water and dissolved nutrients
  
  • temporary and small in animal cells, storing glycogen in the liver and muscles
  • permanent and large in plant cells, storing starch in sinks, roots and leaves
• Lysosome — sacs containing digestive enzymes that digest food and break down worn-out cell parts
• Ribosomes (80s) — site of protein synthesis. attached to rER used outside the cell or are freely suspended in cytoplasm used inside the cell.
• Mitochondria — site of aerobic respiration, produces energy in the form of ATP from glucose
• Secretory vesicle — sac carrying proteins from the golgi apparatus to the cell membrane for secretion
• Smooth ER - synthesizes lipids and buds off to form transport vesicles.

Question 4

Differentiate prokaryotes from eukaryotes

Answer 4

• Prokaryotes reproduce through binary fission, eukaryotes through meiosis and mitosis.
• Prokaryotes has 70S ribosomes, eukaryotes have 80S ribosomes.
• Eukaryotes are compartmentalized, prokaryotes are not.
• Prokaryotes has a nucleoid, eukaryotes have a nucleus.

Question 5

Atypical cell structures

Answer 5

• Striated muscle fibres (multiple nuclei)
• Aseptate hyphae (no septa)
• RBC (no nucleus or mitochondria)
• Phloem (no nucleus)