4. Diversity of Life
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Prokaryotes
Eukaryotes
How did bacteria evolve?
1) The first anaerobic prokaryotic cells appeared on Earth about 3.5 billion years ago. These cells, which are the most ancient known form of life, were simple and lacked a nucleus or other membrane-bound organelles. Bacteria, which are a type of prokaryote, are still found on Earth today and are important for a variety of ecological processes.
2) Photosynthetic bacteria, which are capable of producing their own food through photosynthesis, appeared on Earth shortly after the first prokaryotes. These bacteria released oxygen as a by-product of photosynthesis, which accumulated in the atmosphere. It had 2 main effects:
(a) The presence of oxygen in the
atmosphere led to the mass extinction of
many organisms that were not able to
survive in an oxygen-rich environment.
(b) The increased oxygen levels in the atmosphere formed the ozone layer, which protects life on Earth from harmful UV radiation. This facilitated the colonization of land by organisms, as it allowed for the development of more complex life forms that were able to survive in terrestrial environments.
What are Eukaryotes?
Eukaryotic cells are larger and more complex than prokaryotic cells, and they have a nucleus and other membrane-bound organelles. It is believed that eukaryotic cells evolved from prokaryotic cells through a process known as endosymbiosis, in which one type of prokaryote lived inside another prokaryote and eventually became a permanent part of the host cell.
The Endosymbiotic Theory
Organelles such as mitochondria and chloroplasts, which are important for energy production and photosynthesis, respectively, are thought to have originated through endosymbiosis. These organelles are thought to have evolved from prokaryotic cells that lived symbiotically within host eukaryotic cells, contributing to the complexity of eukaryotic cells.
What are the advantages of Eukaryotes?
Single-celled eukaryotes, which are a type of cell that is more complex than prokaryotes, developed sexual reproduction as a way to increase genetic diversity. Sexual reproduction involves the exchange of genetic material between two individuals, resulting in offspring that are genetically different from their parents. This increases the rate of evolution because it produces a greater variation in offspring, increasing their ability to adapt to changing environments. This is because different combinations of genetic material may lead to the development of traits that are better suited to the environment.
Multicellular organisms, which are composed of many specialized cells that work together to perform specific functions, developed from colonies of undifferentiated cells. These colonies of cells became organized and specialized, leading to the development of tissues and organs. Multicellular organisms also exhibit division of labour, which is the specialization of cells to perform specific functions. This allows for increased efficiency and the ability to perform more complex tasks.
Major Problem with multicellularity
As multicellular organisms increase in size, they face the problem of maintaining a sufficient surface area to volume ratio. This is because a larger organism has a greater volume, but its surface area does not increase at the same rate. This can lead to problems with obtaining nutrients and removing waste. However, the development of specialized cells and tissues can help to solve this problem by increasing the surface area available for exchange.