Biology Chapter 2

• Cells

  Basic functional units of all living organisms
• Cells

  • Simplest organisms are made up of single cells which perform all functions of life
  • Complex organisms are composed of millions of cells
  • In multicellular organisms, there may be hundreds of different types of cells with different structures. They are specialized to carry out particular functions in plants or animals.
• Organelles

  Subunits that cells are made up of, often of a particular size but all microscopically small
• Cell Theory

  1. Cells are the building blocks or basic structures in all living things

  2. Cells are the smallest units of living things, they are the basic units of organization of all organisms

  3. All cells are derived from other cells (pre-existing cells) by means of division

  4. Cells contain a blueprint (i.e. information) outlining their growth, development and function

  5. Within cells there are sites and structures where the chemical reactions of life occur (metabolism)
• Prokaryotic and Eukaryotic Cells

  • Both types of cells are bounded by the plasma membrane which is semipermeable

  Inside the cells is a semifluid jelly-like substance called cytoplasm, in which cellular organelles are suspended

  All cells contain chromosomes which carry genes in the form of DNA

  All cells have ribosomes, tiny organelles that make proteins according to instructions from the genes
• A microscope with a high magnification and resolution is needed to observe cells and their subunits.
• Prokaryotic cells

  Cells of bacteria and archaea
• Eukaryotic cells


  Cells of protists, fungi, plants and animals
• Prokaryotic cells evolved


  Before eukaryotic cells
• Prokaryotic cells


  • Lack a true nucleus
  • Nuclear materials not bound by a nuclear membrane
• Eukaryotic cells

  • Possess a true nucleus
  • Nuclear materials bound by a nuclear membrane
• Prokaryotic cell size

  0.1 - 5.0 μm in diameter
• Eukaryotic cell size

  Typically 10 - 100 μm in diameter
• Eukaryotic cell: an animal cell


  • DNA located in the nucleus, which is bounded by a double membrane
  • DNA is linear and made up of nucleic acid and proteins called histones
• Prokaryotic cell

  • DNA is concentrated in a region called the nucleoid, which is part of the cytoplasm and not membrane bound
  • DNA is circular and contains only nucleic acid with no proteins
• Prokaryotic vs eukaryotic cells

  Membrane bounded organelles are present in eukaryotic cells, but not in prokaryotic cells
• Eukaryotic cells

  Cell walls are absent except in plants and fungi
• Prokaryotic cells

  Cell walls are present
• Prokaryotic cell

  • Average diameter is 0.1 - 5 μm
  • Single copy DNA, circular and contains only nucleic acid with no proteins
  • DNA is located in the cytoplasm
  • Nucleus absent
  • Ribosomes are about 20 nm in size
  • No membrane bounded organelles
  • Cell wall present, made up of murein, a peptidoglycan
• Eukaryotic cell

  • Average diameter is 10- 100 μm
  • Multiple copies DNA, linear and made up of nucleic acid and proteins
  • DNA is located in the nucleus, chloroplasts and mitochondria
  • Nucleus present
  • Ribosomes are about 25 nm in size
  • Membrane bounded organelles present
  • Cell wall present in plants and fungi only, made up of cellulose or lignin in plants and chitin in fungi
  • Cell wall absent in animal cell
• The major difference between prokaryotic and eukaryotic cells is the location of their DNA.
• Eukaryotic cell structure


  • Plant and animal cells have common features which include a plasma membrane (cell membrane), a nucleus and cytoplasm
  • Not all the ultrastructures of a cell are seen with a light microscope
• Cells of different organisms and even cells within the same organisms are very diverse in terms of shape, size, internal organization and function
• Form follows function


  A cell's function influences its physical features
• The diversity in cell shape and structure reflects the different functions of cells
• Cell components present in most plant and animal cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
• Other cell components may be present or absent in plant and animal cells
• One theme that occurs repeatedly throughout biology is that form follows function.
• Plant and animal cells have common features which include a plasma membrane( cell membrane), a nucleus and cytoplasm.
• Not all the ultrastructures of a cell are seen with a light microscope.