Cell Structure and Composition: Prokaryotes vs Eukaryotes

Cell Structure and Composition

• The largest cell is the egg of an ostrich, measuring 17cm x 13cm.
• Cells can be classified into two main categories: Prokaryotes and Eukaryotes.

Prokaryotes

• Characterized by a relatively simple morphology and lack of a true membrane-delimited nucleus.
• Have a single circular chromosome (1 chromosome) and no membrane-enclosed organelles.
• Ribosomes are the only membrane-bound organelles.
• Cell walls typically consist of polysaccharide peptidoglycan.
• Reproduce by binary fission (no mitosis).
• Examples include bacteria, rickettsia, and blue-green algae.

Eukaryotes

• Characterized by a true membrane-enclosed nucleus.
• Have more than one chromosome and numerous membrane-bound organelles.
• DNA is associated with histone proteins.
• Divide by mitosis.
• Cell walls are chemically simpler than prokaryotes.
• Examples include plant and animal cells.

Comparison of Prokaryotes and Eukaryotes

• Prokaryotes lack a nucleus, organelles, and have a cell wall made of peptidoglycan.
• Eukaryotes have a nucleus, organelles, and may have a cell wall made of cellulose or chitin.

Plant and Animal Cells

• Both have a cell membrane, nucleus, and cytoplasm.
• Plant cells have a cell wall, while animal cells do not.
• Plant cells have plastids, while animal cells do not.

Classification of Organisms

• The Binomial System of Nomenclature is used to classify organisms.
• Whittaker's five-kingdom system is based on the following criteria:
  • Kingdom Animalia (animals): multicellular, have nuclei, can move, and are heterotrophic.
  • Other kingdoms include Plantae, Fungi, Protista, and Monera.

Taxonomic Classification

• The classification system consists of seven levels: Domain, Kingdom, Phylum, Class, Order, Family, and Species.
• The three domains are: Bacteria, Archaea, and Eukarya.
• Domain Eukarya is further divided into four kingdoms: Plantae, Animalia, Fungi, and Protista.

Domain Archaea

• Single-celled organisms that lack a membrane-bound nucleus.
• Can be found in environments that are too hostile for other life forms.

Domain Bacteria

• Single-celled organisms that lack a membrane-bound nucleus.
• Found almost everywhere on the planet Earth.

Domain Eukarya

• Cells have a membrane-bound nucleus.
• Members of this domain are further categorized into one of four kingdoms.

Learn about the structure and composition of prokaryotic and eukaryotic cells. Explore the differences in morphology, nucleus presence, organelles, and other cellular components.