1.2 Cell structure and organisation

• What is the cell theory?

  A unifying concept in biology
• What does the cell theory state about new cells?

  New cells are formed from existing cells
• What is the fundamental unit of structure in living organisms?

  The cell
• What surrounds all living cells?

  A cell/plasma membrane
• What does the cell membrane provide?

  A barrier between cytoplasm and environment
• What is contained within the cytoplasm?

  Specialised structures called organelles
• What is the function of organelles?

  They carry out specific functions within a cell
• What may be present outside the cell membrane?

  A cell wall
• How long ago is it believed that life evolved?

  Over 3.8 billion years ago
• What type of cells are believed to be the earliest organisms?

  Prokaryotic cells
• Why are prokaryotic cells named so?

  Their DNA is not enclosed in a nuclear membrane
• What is the size range of prokaryotic cells?

  Between 0.2 and 5 µm
• What is the generalised structure of a prokaryotic cell?

  • No nuclear membrane
  • Small size (0.2 to 5 µm)
  • Contains DNA
  • Surrounded by a cell membrane
• Eukaryotic cells

  Eukaryotic cells are believed to have evolved from prokaryotic cells. The most obvious difference between them is that the DNA is no longer free in the cytoplasm but is contained within a nuclear membrane. Plants, animals and fungi are multicellular eukaryotic organisms. Protoctista are unicellular eukaryotic organisms.

  Eukaryotic cells are larger than prokaryotic cells, 10-100µm, and have more and different organelles. Many of the organelles are membrane-bound organelles, not found in prokaryotic cells. The diagrams below represent typical plant and animal cells.

  
• Differences between prokaryotic and eukaryotic cells

  
• Why are viruses not considered alive?

  They lack a cell membrane
• What do viruses lack that makes them non-cellular?

  They have no cytoplasm
• Why can't viruses carry out respiration?

  They cannot synthesize ATP
• Do viruses grow like living organisms?

  No, they do not grow
• How do viruses replicate?

  They invade a host cell
• What must viruses use to produce more virus particles?

  Host cell's metabolic processes
• What are the basic components of a virus?

  • Protein coat (capsid)
  • Enzymes for viral replication
  • DNA or RNA molecule
• What is the protein coat of a virus called?

  Capsid
• What are capsomeres?

  Individual units of the capsid
• What does the viral genetic material contain?

  A small number of genes
• What essential proteins are coded by viral genes?

  Capsid proteins and replication enzymes
• What is a viral envelope?

  An additional layer outside the capsid
• What is the composition of a viral envelope?

  Phospholipid bilayer from host cell
• What role do viral proteins play in the envelope?

  They help penetrate host cell membrane
• What function do glycoproteins serve in viruses?

  They act as receptor molecules
• How do glycoproteins facilitate viral entry into host cells?

  They bind to host cell receptors
• What are the structural differences between a simple virus and a virus with an envelope?

  • Simple virus: only has a capsid
  • Virus with envelope: has an additional viral envelope
• What is the process of exocytosis?

  Secretion of substances from cells
• How does exocytosis affect the plasma membrane?

  It increases the surface area of the plasma membrane
• What is the role of endocytosis?

  To take in substances or food particles
• What happens to the plasma membrane during endocytosis?

  It decreases in surface area
• How do the nucleus, endoplasmic reticulum, Golgi body, and plasma membrane work together?

  • Enable cells to take in large food particles
  • Digest food particles internally
  • Synthesize, process, and package enzymes
  • Release enzymes for external digestion
• What is formed during endocytosis when the plasma membrane surrounds particles?

  Phagocytic vesicles
• What is the effect of exocytosis on the membrane composition?

  It adds new membrane to the plasma membrane
• What type of particles can cells take in through endocytosis?

  Large food particles, including bacteria