Enzymes are important for allowing and speeding up reactions in an organism. They do this by orienting chemical compounds and or substances so that they can easily break and form new products easily, the activation energy is lowered upon the use of such enzymes.
There are all sorts of ways to reconstruct the history of life on Earth. Pinning down when specific events occurred is often tricky, though. For this, biologists depend mainly on dating the rocks in which fossils are found, and by looking at the “molecular clocks” in the DNA of living organisms.
There are problems with each of these methods. The fossil record is like a movie with most of the frames cut out. Because it is so incomplete, it can be difficult to establish exactly when particular evolutionary changes happened.
Modern genetics allows scientists to measure how different species are from each other at a molecular level, and thus to estimate how much time has passed since a single lineage split into different species. Confounding factors rack up for species that are very distantly related, making the earlier dates more uncertain.
These difficulties mean that the dates in the timeline should be taken as approximate. As a general rule, they become more uncertain the further back along the geological timescale we look. Dates that are very uncertain are marked with a question mark.
Animal skulls are said to protect the one of the most important organ in the body. Moreover, the bone has also some features that are important such as being able to identify the organ of the animal, knowing somehow the lifespan, diet and other similar biological traits.
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When you breath in you breath in oxygen, which comes from plants, when you breath out, you breath out carbon dioxide, which is what plants breath.