Information on Cells

Cells are the basic building block of living organisms. Some organisms are single-celled, while others have evolved into multicellular plants or animals. The more primitive prokaryotic cells are single-cells. The more complex eukaryotic cells may be single-celled, colonial, or multi-celled. Prokaryotes and eukaryotes also exhibit differences in cell structure and internal organization.

The Facts About Cells

The cell is the smallest living unit. Some cells live as single-cell organisms, while others serve as building blocks for multicellular organisms. All cells are derived from pre-existing cells. Cells are generally self-contained and self-maintaining. Each cell is able to take in nutrients, convert nutrients to energy, execute special functions, and reproduce. Each cell stores the necessary information to perform all functions independently within the cell. All cells will respond to internal and external stimuli such as nutrient levels, light, and temperature.

The Types of Cells

Cells are classified into two major divisions: the prokaryotes and the eukaryotes. Prokaryotic cells do not exhibit a well defined nuclear membrane in the cell. The name prokaryote means: "before" (pro-) the nucleus, or "karyon" (Greek: "nut"). The eukaryotic cell has a defined or "true" (eu-) nucleus. Prokaryotic cells are more primitive than eukaryotic cells. Prokaryotic organisms are single-celled organisms such as archaea and bacteria. Eukaryotic cells exist as single-cell, colonial, and multicelled organisms.

Prokaryotic Cells

Prokaryotic cells are distinguishable because they do not have a nuclear membrane or membrane enclosed organelles. The metabolic functions of the cell are performed by the plasma membrane. The prokaryotic cell usually has a cell wall. The cell wall of bacteria (Eubactera) contains peptidoglycan, while the Archaea cell walls do not. Prokaryotes have their genetic material, Deoxyribonucleic acid (DNA), dispersed throughout the cytoplasm. The prokaryotic DNA is arranged in a single circular configuration. Prokaryotic cell reproduce by binary fission. They replicate their genetic material and divide into two daughter cells. This limits genetic diversity and keeps each generation of cells the same

Eukaryotic Cells

The eukaryotic cells are those that have a true ("eu") nucleus ("karyon"). The nucleus of the eukaryotic cell, containing the genetic material, is separated from the cytoplasm by a discrete membrane, the nuclear membrane. The DNA of eukaryotes is arranged linearly in paired strands forming the chromosomes. The cytoplasm of the eukaryotes contains organelles that also are bound by membranes. The mitochondria and chloroplasts are organelles that have a function in energy conversion and metabolism in the cell. These organelles are enclosed in separate endoplasmic membranes. Chloroplasts are only seen in eukaryotes that perform photosynthesis. The mitochondria and chloroplasts each contain their own DNA. This has led to cell biologists to believe that these organelles evolved from symbiotic prokaryotes that associated with eukaryotic cells early in the evolution of the eukaryotes. Other organelles contained in membranes include Golgi apparatus, endoplasmic reticulum, lysosomes, and vesicles that serve various functions in metabolism and storage. Eukaryotic cells can reproduce by mitosis (binary fission producing identical daughter cells) or by meiosis (sexual reproduction). Meiosis occurs when individual strands of paired chromosomes separate into individual strands to donate one-half of the parent cell genetic information.

Types of Eukaryotes

Eukaryotic cells can be separated as plant or animal cells. The plant cells usually have a cell wall outside of the cell membrane which animal cells lack. Photosynthetic plants will have chloroplasts in their cytoplasm while animal cells do not have these organelles. Eukaryotic cells can be found as singular organisms, associated colonial organisms, or as multicellular organisms. Eukaryotic cells can become specialized in multicellular organisms to form tissues and organs with specific structure and function. Eukaryotes are generally larger than prokaryotes. The eukaryotes have a cell diameter that ranges from 10 microns to 1 millimeter compared to a range of 1 micron to 10 microns for prokaryotes.

Resources

• The Prokaryotes