Eukaryotic cells are characterized by membrane-bound organelles. Except for red blood cells, which lose their nucleus at maturity, every eukaryotic cell contains a membrane-bound nucleus, which houses the cell's DNA. Other membrane-bound organelles include mitochondria, chloroplasts and other plastids, lysosomes, peroxisomes, vacuoles, and vesicles. Still other membranous organelles include the endoplasmic reticulum and Golgi apparatus. Ribosomes, centrioles, flagella, and cilia are among the few organelles that are not bound by cell membranes. Prokaryotic cells do not have these membrane-bound organelles but instead have other structures, such as the nucleoid, to carry out life functions. A cell's size is limited by its surface-area-to-volume ratio because the cell's surface area must be large enough to take in nutrients and let out waste. Cells can be viewed under microscopes—light microscopes use beams of light, while transmission electron microscopes and scanning electron microscopes use beams of electrons. Some kinds of cells can be grown in laboratories in artificial media in a process called tissue culture.
At A Glance
- Both eukaryotic and prokaryotic cells have some organization in common: they are enclosed in a cell membrane, which surrounds the cytoplasm (a combination of cytosol and organelles, excluding the nucleus), and they contain genetic material that encodes instruction for life processes.
- Eukaryotic cells are organized to contain several membrane-bound organelles and a nucleus that directs the functions of these organelles.
Organelles found in eukaryotes and prokaryotes have specific cell tasks. For example, the nucleus in eukaryotes contains information in the form of DNA.
Other organelles found in eukaryotic cells include the endoplasmic reticulum, ribosomes, the Golgi apparatus, and various other structures suspended in the cytosol.
- Prokaryotic cells lack membrane-bound organelles but include other structures such as the nucleoid, where the cell's genetic material is stored.
Cell size is limited by the cell's surface-area-to-volume ratio, such that cells cannot become so large that the surface of the cell is insufficient to take in nutrients and remove wastes.
- Plant cells were first viewed in the mid-1600s by Robert Hooke, who used a very simple light microscope to view the cell walls in dead cork cells.
Modern microscopy involves the use of light microscopes (including fluorescence microscopes), transmission electron microscopes (TEMs), and scanning electron microscopes (SEMs).
- Some kinds of cells can be maintained in vitro by growing them in artificial media, a process known as tissue culture.
- In order to better understand how organisms function, scientists often examine easily studied model organisms.