Cell Types

• The two main types of cells are prokaryotic cells and eukaryotic cells. Prokaryotic cells are small, simple cells. These cells---commonly known as bacteria---appear in three main shapes including cocci (a spherical shape), bacilli (a rod shape) and spirilla (a spiral shape). Prokaryotic cells do not have organelles. Their DNA sits in an area called the nucleoid region. Eukaryotic cells are much larger and more complex than prokaryotic cells. Eukaryotic cells have specialized organelles. Their DNA is enclosed in a membrane-bound nucleus.
  
  

Cell Parts

• All cells (prokaryotic and eukaryotic) contain three main elements. This includes the cell's own genetic material (DNA) which governs its operations, a cell membrane surrounding the cell and a fluid-like substance called cytoplasm that fills the cell. Eukaryotic cells however, also contain specialized structures called organelles that perform specific functions in the cell. The nucleus controls cell division and regulates the function of the entire cell. Mitochondria manufacture energy for the cell. The Golgi apparatus processes and organizes certain molecules. Lysosomes break down molecules of food. Plant cells have organelles called chloroplasts that create energy through photosynthesis.
  
  

Cell Reproduction

• All cells have the ability to reproduce. When a cell reproduces, the parent cell duplicates its DNA and divides to form two identical daughter cells. Each daughter cell receives a copy of the original cell's genetic material. Prokaryotic cells reproduce in a process called binary fission. Eukaryotic cells reproduce in a process called mitosis. Mitosis occurs in four main phases which include prophase, metaphase, anaphase and telophase. In multi-cellular organisms, cell reproduction functions to replace cells that are damaged or old, and contributes to the organism's growth.
  
  

Discovery

• The cell was discovered by 17th century scientist Robert Hooke who published his observations in his work Micrographia in 1665. Hook discovered cells while examining a piece of cork under a microscope. Since cork is derived from a species of oak tree called the cork oak, Hooke was actually looking at dead plant cells. Hooke felt that the regions he saw resembled a monk's chambers so he called them cells. Later,19th century botanist Matthias Schleiden and zoologist Theodor Schwann would each contribute to the formulation of a complete cell theory. In 1838, Schleiden proclaimed that all plant tissues are made of cells. In 1839, Schwann added that all animal tissues are made of cells and that all life begins as a single cell.
  
  

Stem Cells

• New research and discoveries involving the cell continue to change the face of modern science and medicine. Human embryos contain what are called stem cells. Human embryonic stem cells are very unique. While they are still unspecified at this stage, these cells have the ability to become any type of specialized cell in the human body such as skin cells or nerve cells. As a result, scientists believe that stem cells may have the potential to treat a wide range of diseases including heart disease and Alzheimer's disease. However, a heated debate is currently underway over the ethical implications of using human embryonic stem cells.