biology 1.2

• Prokaryotes


  Cells that do not have a membrane-bound nucleus
• Prokaryotic cells


  • Have a cell wall that surrounds the cell membrane
  • Carry DNA in the cytoplasm where it is organised into a single circular chromosome
  • Contain simple sub-cellular components that lack a membrane, e.g. ribosomes
  • Exist as single cells, or are unicellular
• Shapes of prokaryotes


  • Rods
  • Spheres
  • Spirals
• The different shapes of prokaryote cells occur singly, in pairs, or in chains of many cells
• Chains of prokaryotes may include single rod-shaped, spherical, and spiral-shaped prokaryote cells
• Eukaryotes


  Cells that have a membrane-bound nucleus
• Eukaryotic cells


  • Can have a variety of sub-cellular components called membrane-enclosed organelles
  • Are significantly larger than prokaryote cells
  • Animal and plant cells are both eukaryotic cells, but the structure differs in several ways
• Differences between animal and plant eukaryotic cells

  • Plant cells have a cell membrane surrounded by a cell wall, animal cells do not
  • Plant cells have a large number of large permanent vacuoles, animal cells do not
  • Plant cells have organelles called chloroplasts, animal cells do not
• The membrane-enclosed organelles in eukaryote cells have a variety of functions
• Functions of membrane-enclosed organelles in eukaryotic cells

  • Making important biological molecules, e.g. proteins
  • Performing biochemical reactions, e.g. aerobic cell respiration and photosynthesis
  • Secretion of substances made by the cell, e.g. proteins
  • Removal of wastes, e.g. carbon dioxide
• Nucleus


  Stores the genetic information/DNA and controls/coordinates the overall function of the cell
• Organelles found in eukaryotic cells

  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Golgi body
  • Mitochondrion
  • Vacuole
  • Chloroplast