Introduction to Cells
Biology: IB Diploma Higher Level, topic 2.2.1
Introduction to Cells
According to the cell theory, all living organisms, from bacteria to humans, are composed of cells, the smallest units of living matter.
Cell size
- Cells are often too small to be seen without a microscope.
- Cells come in all sizes and shapes.
- Their small size allows for a large surface-area-to-volume ratio that enables a more efficient exchange of nutrients and wastes with the environment.
Types of cell
- There are three basic types of cells: archaea, bacteria, and eukaryotes.
- Both archaea and bacteria are classified as prokaryotes, whereas cells of animals, plants, fungi, and protists are eukaryotes.
- Archaea are a unique group of organisms and likely evolved in the harsh conditions of early Earth and are still prevalent today in extreme environments, such as hot springs and polar regions.
Common ancestry
- All three types of cells share features that reflect their evolution from a common ancestor.
- These features are:
- A plasma membrane that separates the cell from its environment
- Cytoplasm comprising the jelly-like cytosol inside the cell
- Ribosomes that are important for the synthesis of proteins
- DNA to store and transmit hereditary information
Prokaryotes vs eukaryotes
- The term “prokaryote” means “before nucleus,” and prokaryotes do not have nuclei.
- Rather, their DNA exists as a single circular chromosome in the central part of the cell called the nucleoid.
- Eukaryotic cells possess many features that prokaryotic cells lack, including a nucleus with a double membrane that encloses DNA.
- In addition, eukaryotic cells tend to be larger and have a variety of membrane-bound organelles that perform specific, compartmentalized functions.
Test yourself on Introduction to Cells
The presence of which of the following differentiates a eukaryotic cell from a prokaryotic cell?
Which of these is NOT one of the three basic types of cells?