The Precambrian era envelopes the major bulk of the history of the Earth, beginning from the creation of the planet approx 4.5 billion years ago and terminating with the origination of composite, multicelled forms of life approximately 4 billion years after.
The Precambrian refers to the earliest of the geologic ages that are signified by the distinct layers of sedimentary rock. The Earth was about more than six hundred million years old when life started. The planet had cooled down from its native molten state, creating a solid crust and oceans formed by water vapor in the atmosphere.
At about three billion years ago, the atmosphere of the Earth was virtually devoid of oxygen. At approximately 2.4 billion years ago, oxygen was discharged from the seas as a waste product of photosynthesis by cyanobacteria. The levels of the gas slowly raised, attaining about 1 percent around two billion years ago.
Approximately 800 million years ago, the levels of oxygen attained about 21 percent and started to breathe life into more composite species. The oxygen-rich ozone layer was also created, protecting the surface of the Earth from the harmful solar radiation.
The parent cells are diploid.
An adaptation-----------------------
What is a gene?
- According to Mendel something was being stably passed down, unchanged, from parent to offspring through the gametes, over successive generations. He called these things as ‘factors’ now called as genes. Genes, therefore, are the units of inheritance.
- They contain the information that is required to express a particular trait in an organism.
- Genes which code for a pair of contrasting traits are known as alleles, i.e., they are slightly different forms of the same gene.
- There is no ambiguity that the genes are located on the DNA, it is difficult to literally define a gene in terms of DNA sequence.
- The DNA sequence coding for tRNA or rRNA molecule also defines a gene. A cistron is defined as a segment of DNA coding for a polypeptide, the structural gene in a transcription unit could be said as monocistronic (mostly in eukaryotes) or polycistronic (mostly in bacteria or prokaryotes).
To learn more about transcription:
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Hi
Do prokaryotic organisms carry out cellular respiration? If so, how?
The answer is yes as well as no, because some prokaryotes like Archeae and some bacteria donot use cellular respiration because they are anaerobic. The Archaea are also known as Methanogens that reduce Carbon di oxide from environment to Methane that is eventually oxidized to NADH (that is used as an energy source).
However, there are some bacteria that use cellular respiration as a source for the energy production.Cellular respiration is a process which occurs in the cells of higher living organisms as well as in cells of some small organisms like Bacteria. During process of cellular respiration in bacteria, glucose is broken down with the help of oxygen into water and Carbon di oxide. In the process of cellular respiration, bacteria just like humans goes through three stepsi.e Glycolysis, Kreb cycle and Electron transport chain that ultimately lead to the production of ATP (energy).
Hope it helps!
