This has happened before in Yellow Stone National Park in CA. Removing a species form the Pyramid causes the ecosystem to collapse, as species become over hunted and others are starved. One type of organism could become overpopulated, therefor lack of natural variation.
Answer:
movement to and fro or around something, especially that of fluid in a closed system.
The valves are responsible for preventing blood from flowing in the wrong direction, they are present in the veins, and the arteries don't need them because the aorta (biggest artery) pumps or in other words pushes it with such a force that no other force can change its direction, in the veins there is no structure present for pumping them as a result we have got valves so that they go in one direction...... the meaning of the word valve is to allow in one direction
Answer:
Eukaryotic cells arose through endosymbiotic events that gave rise to the energy-producing organelles within the eukaryotic cells such as mitochondria and chloroplasts. ... The endosymbiotic theory proposes that one organism engulfed another, and the two co-evolved together until they could not exist independently.
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