Levels of Organization Image Map

Cells are small. How small? See the diagram below that shows the size relationships of cells relative to larger and smaller things.

csizescale.gif (17821 bytes)


Most cells can be seen with a light microscope. The chart shows a huge range of sizes, from fractions of a nanometer of atoms to the meter sizes of humans.

Big-Picture Time


First, let us step back and get the big picture on the size of cells. We know cells are small, but how small? The chart below shows the relative sizes (on a logarithmic scale) of a typical cell, compared with the sizes of other things in nature.


Structure and Function

Now let's learn the different parts and functions of cells. Here we want to think about how the organization inside each cell keeps them alive and well.

The chart below gives some examples of how living things assign and divide up jobs that are needed for breathing to occur. 

Example Function (Job):

Name of Structure

Level of Organization

  • control of breathing
  • breathing
  • gas exchange in lungs
  • blood pumping
  • oxygen transport
  • energy production
  • oxygen binding/release
  • nervous system
  • lungs
  • alveoli
  • heart
  • red blood cells
  • mitochondria
  • hemoglobin
  • organ system
  • organ system
  • tissue
  • tissue
  • cells
  • organelles
  • molecules

Cells are organized by the jobs they perform in living things. The main jobs of cells are as follows:


Detailed Tasks

Hold cell materials together Regulate which molecules can go in and out of cells. Detect chemical signals outside of cells and translate "message" to inside.
Capture and use energy Plant cells - trap energy of sunlight. Animal cells - convert energy of food.
Make protein Repair, provide building materials for growth and for new cells.
Make new cells Control division to make new cells. Sex cells: reduce the genetic material by half.

What Performs the Work of Cells 

Cells contain certain smaller structures, known as organelles. They perform the work of cells. Organelles are thus one level of organization for life functions.

Details on what these organelles do are given in the other units of "Cells Are Us." 

Cell Function Chart

For a 3-dimensional drawing of a cell and its organelles, click here.

For animated illustrations of each organelle and its functions, click here. (At this site, click on the name of each organelle to see animation and explanation).

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