The Five Kingdoms.

Traditionally, all living things have been grouped into a number of kingdoms. For many years, the generally accepted number of kingdoms was two. All living things were grouped into either plants or animals. As more living things were discovered and studied closely, it became clear that not all living things could fit easily into one of these categories. For some years now, the accepted number of kingdoms has been five.

The prokaryotes are the organisms belonging to the kingdom Prokaryota (which used to be called the Monera). These organisms include the bacteria and the cyanobacteria (these used to be called blue-green algae). Prokaryote means 'before nucleus'. The main feature of all the prokaryotes is given in their name - they evolved before the nucleus became the place to keep DNA. So all prokaryotes have no nucleus. The prokaryotes:

• have no nucleus
• have a loop of naked DNA (DNA that is not associated with histore proteins) that is not arranged in linear chromosomes
• have no membrane-bound organelles
• have smaller ribosomes than in other groups
• carry out respiration not in mitochondria, but on special membrane systems (mesosomes)
• have cells smaller that those of eukaryotes
• may be free-living or parasitic; some cause diseases

All members of the kingdom Protoctista are eukaryotes. This group contains organisms that are single-celled. It also contains some multicellular organisms, e.g. algae. (The smaller members of this kingdom used to be known as protists.) The protoctists:

• are eukaryotes
• are mostly single-celled
• show a wide variety of forms
• shows various plant-like or animal-like features
• are mostly free-living
• have autotrophic or heterotrophic nutrition - some photosynthesise, some ingest prey, some feed using extracellular enzymes (like fungi do), and some are parasites

The only thing that all Protoctists have in common is that they do not qualify to belong to any other four kingdoms!

The members of the kingdom Fungi are a group of organisms in which the body consists of a mycelium - a network of numerous strands called hyphae. The cytoplasm is surrounded by a wall of a polysaccharide called chitin. The cytoplam is usually not divided into cells. It has many nuclei (it is multinucleate). A few fungi are cellular. The fungi:

• are eukaryotes
• have a mycellium, which consists of hyphae
• have walls made of chitin
• have cytoplasm that is multinucleate
• are mostly free-living and saprophytic - this means that they cause decay of organic matter

The green plants (kingdom Plantae) are all multicellular organisms. They gain their nutrition from photosynthesis. This means they are autotrophs. The plants:

• are eukryotes
• are multicellular
• have cells surrounded by a cellulose cell wall
• produce multicellular embryos from fertilised eggs
• have autotrophc nutrition

The animals (kingdom Animalia) are multicellular organisms that gain their nutrition by digesting and absorbing organic matter - they are heterotrophic. The animals:

• are eukaryotes
• are multicellular
• have heterotrophic nutrition
• have fertilised eggs that develop into a ball of cells called a blastula
• are usually able to move around