The answer is an ecosystem.
Microfilaments
Microfilaments are fine, thread-like protein fibers, 3-6 nm in diameter. They are composed predominantly of a contractile protein called actin, which is the most abundant cellular protein. Microfilaments' association with the protein myosin is responsible for muscle contraction. Microfilaments can also carry out cellular movements including gliding, contraction, and cytokinesis.
Microtubules
Microtubules are cylindrical tubes, 20-25 nm in diameter. They are composed of subunits of the protein tubulin--these subunits are termed alpha and beta. Microtubules act as a scaffold to determine cell shape, and provide a set of "tracks" for cell organelles and vesicles to move on. Microtubules also form the spindle fibers for separating chromosomes during mitosis. When arranged in geometric patterns inside flagella and cilia, they are used for locomotion.
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They are able to travel in a vacuum at the same speed.
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Answer:
D. Mass extinction events separate the three eras from each other
Explanation:
The Phanerozoic represents an eon, and it is the most recent one. It is further divided into three eras, Paleozoic, Mesozoic, and Cenozoic. The division between the tree eras is because of mass extinction events. The Paleozoic and Mesozoic era are divided by the Permian-Triassic mass extinctions. The Mesozoic and Cenozoic are divided by the Cretaceous-Paleogene extinction. The Cenozoic era is still in existence, as there hasn't been a mass extinction of a magnitude big enough so far.
