Cell Structure Plants & Animals
Life seemed so simple - not so very long ago. There were two "kingdoms", Vegetabilia and Animalia. But entities were found that just didn't seem to fit comfortably, so Vegetabilia was divided into Plantae (entities that were definitely plants) and Protista (entities that didn't seem to be either plants or animals). Then it got complicated, up to 8 kingdoms, and now the whole kingdom concept has pretty much collapsed.

Fortunately, for culinary purposes, we can simplify things quite a bit, by simply ignoring a bunch of whole "kingdoms" that aren't particularly edible. So here we present our "Tree of Life", considering only edible branches.   Illustration of Eukaryote Cell Structure by Mariana Ruiz contributed to the public domain (click on it for larger).


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In the Beginning was LUCA

About 4 billion years ago, when the Earth was only a half billion years old, LUCA (Last Universal Common Ancestor) came to be. From LUCA evolved two domains of life: Bacteria and Archaea. Genetic research has placed LUCA in a hot, toxic, metal-laden, gassy environment, very like the hot, toxic, metal-laden, gassy environment of the deep sea vents that still exist today. Similar conditions probably also existed on the surface in those formative times. The intense debate as to whether LUCA was alive, or just "half alive", or formed in the deep sea or on the surface, are entertainments for specialists and need not concern us here.

Domain Eukaryota

These are the "higher" life forms, with a much more complex cell structure than Bacteria or Archaea. It is now pretty certain that Eukaryots are an advanced form of Archaea, as living transition forms have been found. The big difference is that some bacteria engulfed by Archaea were not digested, but took up residence in the cells, eventually evolving into Mitocondria, but still with their own separate DNA. The Archaea cells set up Internal membranes to keep these mutually beneficial arrangements orderly, forming Eukaryotes. Eukaryotes are unique in their ability to organize into large, complex multi-cellular entities. This allowed Eukaryotes to develop sexual reproduction. Evolution was extremely slow until the invention of sex - then it took off like gangbusters.

Opisthokonta:   The Animals and Fungi, descending from a common Eukaryote ancestor, live by breaking down and digesting dead and living plant and animal material. There are no significant exceptions.

Archaeplastida:   Plants were formed by Eukaryots already containing Mitochondria. These also engulfing a form of Cyanobacteria, which evolved into Chloroplasts. These Cyanobacteria enable plants to generate their own food from sunlight, carbon dioxide and minerals, and to breath out Oxygen. Like Mitochondria, Chloroplasts have their own separate DNA. To some extent plants also depend on fungi to break down rock to release the minerals they need - and many depend on animals for their reproductive strategy. It is suspected that some plants use the network of fungus mycelium fibers as a sort of Internet, as they have been observed to react to threats affecting plants at a distance from them.

Chromalveolata:   These are similar to plants - but they aren't plants, at least not yet. Red and green algae used to be here, but are now considered plants.

Domain Bacteria

These simple (comparatively) single celled organisms have been with us since LUCA, and remain in the same basic form. They do not have a cell nucleus or internal membranes. Bacteria constitute more of the Earth's biomass than animals and plants together. The human body contains 10 times as many Bacteria cells than Animal Eukaryote cells (they are much smaller), and is dependent on these Bacteria for digestion and some other functions.

For culinary purposes, bacteria are also very important, for things like making vinegar, wine, cheese and many other products. Bacterial fermentation is also important for detoxifying soybeans and similar activities.

Domain Archaea

These single celled life forms are about the size and appearance of bacteria, and were classified as bacteria until 1977. Advanced genetic analysis caused them to be placed in their own domain. Not a lot is yet known about Archaea. They were thought to live mostly in extreme environments but now they have been found in the ocean, soil and the human gut and skin. They are important to life cycles of the planet. Living transition forms have been found deep in sediments off the coast of Antarctica making it clear that Eucaryotes developed from Archaea.

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©Andrew Grygus - agryg@clovegarden.com - Photos on this page not otherwise credited are © cg1 - Linking to and non-commercial use of this page permitted