Size

• Most cells are between 1 and 100 micrometers in diameter and are only visible with a microscope. However, some cells are large enough to be seen with the naked eye. For example, the largest known single cell is the ostrich egg, and there are single-celled amoebas that are the size of grapes and roll along the sea floor.
  
  

Membrane

• All cells are bounded by a semipermeable membrane that regulates what enters and exits the cell.
  
  

DNA

• All cells contain DNA in the form of one or more chromosomes. The DNA contains the information needed to build all the different proteins the cell can make.
  
  

Ribosomes

• All cells contain ribosomes, which make proteins based on the coded information stored in the DNA.
  
  

Nucleus

• Eukaryotic cells (such as plant and animal cells) have membrane-bound organelles, including a nucleus. Prokaryotic cells (such as bacteria) are much smaller and do not have a nucleus or any other membrane-bound organelles.