The Cambrian explosion was a period at the Pre-Cambrian boundary of the geologic time scale at 542 Ma. At this boundary, the fossil record shows that animals suddenly appeared in a dramatic radiation of life. A radiation is the relatively rapid development of new types of organisms that derive from a common ancestor. The Cambrian explosion is important because it marks the origination of all major animal groups called phyla.
The level of productivity in oceans can be explained by the fact that the volume of the global ocean is enormous.
The oceans cover about 70% of the earth. This makes the ocean to occupy the largest volume on earth.
In spite of this large volume, the productivity of the ocean is just about 55 billion tons.
This low productivity of the ocean is tied to its large volume and small amount of primary productivity.
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I believe option B would be the correct choice because, without a catalyst, the reaction will be either too slow or will not happen at all as it would not acquire a fitting activation energy for the reaction.
If you would like to know why the other options are incorrect, please read on:
Option A is incorrect because since proteins are specific in nature, so other protein cannot be replaced, for some other chemical reaction.
Option C is not correct it is a genetic defect that the protein does not form, and all cells are genetically identical, a reaction cannot take place in any parts of the body.
And finally, option D would be wrong because if a forward reaction does not take place, a backwards reaction will not occur.
I hope this answer has helped, and I apologise if somehow this answer finds itself to be incorrect. Good luck on your quiz or homework. :)