Chapter Nine

Life evolves after a billion or so years - Eukaryote, including Algae

9.1    The next great leap forward in evolutionary complexity, which was to lay the foundation for the development of all complex life forms which are visible to the eye today, was the emergence of the eukaryotes, which began as single celled organisms but with a nucleus.

9.2   One theory of how the first Eukaryotes evolved suggests that a tricky little organism called mitochondria entered into a symbiotic relationship with a prokaryote and thus bestowed on the lucky host great powers of generating energy.  Today mitochondria are found in every single eukaryotic cell on the planet, including in all complex lifeforms including humans.  Much is still being discovered about Mitochondria.  Nick Allen has devoted another book to the subject.  One reviewer slyly refers to enthusiasts for the vast role played by mitochondria as “mitochondriacs”.  No doubt proponents of the primary importance of photosynthesis, way before even the mitochondria turned up on the scene, will be similarly branded “cyanotologists”. But since between them the cyanobacteria and mitochondria supply the pretty much the power of all plant and animal life on earth, the energy with which their roles is acclaimed is arguably not excessive.

9.3   The eon which followed the Archaen, is named the Proterozoic or early life, was characterized by the formation of stable continents, the appearance of abundant bacteria and archaea, and the buildup of oxygen in the atmosphere. By about 1.8 billion years ago the oxygen buildup was significant enough to cause many types of bacteria to die out.  But this “oxygen catastrophe” turned out to open up much great possibilities for more complex life-froms which led to the the arrival of multicelled creatures by around 1.5 billion years ago.  Initially these were just assemblages of identical cells in a colony, but soon the individual cells developed specific structures useful to the whole colony, and this in turn led to even more complex and successful life forms.

9.4   Eurkaryotes developed into diplomonads, and microsporia, and trichomonads, before the arrival of two organisms which to this day play a big role in lake life: the flagellates, so called because they propel themselves by means of a single flagella and ciliates who use a row of tiny hairs or cilia to propel themselves.  Eukaryotes proceed to take a huge step forward in evolution and produce the slime moulds, and then fungi, plants and animals and somewhat later, us.

9.5    The arrival of the eukaryotes was a step change in biological complexity to which even the heretofore all-conquering kings of creation, Cyanobacteria, had to accommodate.  But our hero/ villain Cyanobacteria, was ever resourceful.  It had seen its dominance of the oceans, making the planet’s entire atmosphere oxygen rich, and destroying vast numbers of its bacterial competitors in the process, eventually enabling its successor eukaryotes to evolve into ever more complex forms. It saw what was happening with the arrival of these sophisticated competitors and took a big decision – of the smartest kind.  Seeing the success mitochondria had made of symbiosis, they negotiated a joint venture beneficial to both themselves and the eukaryotes.  They were allowed into the safe environment of the eukaryotes cell wall in return for giving the eukaryote host the ability to photosynthesize – in structures called chloroplasts.

9.6   So cyanobacteria were generous enough to bequeath their unique photosynthetic knowledge to more complex life forms, which exist to this day, not least in Lake Annecy, and are called algae.   Cyanobacteria gave away their patent.   Or rather they traded it for new symbiotic relationships with the new powerful life form on the block, eukaryotes.

9.7   These little chaps became the floating, microscopic vegetation of the ocean and lakes which we now call phytoplankton.  (Q80 p 34) They produce oxygen in water close to the surface.  These microorganisms develop thanks to the energy of the sun, to carbon dioxide and nutritious elements dissolved in the water such as phosphorus, and nitrogen and so transform inert material into life.  Characterized by very numerous species classified by their shape and colour, these microorganisms also serve as food for the other acquatic organisms.

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