I think one major difference with that is that animals can move around, go distances in search for food or mate, and thus make the animal densities per geography vary greatly. Birds migrate regularly, so their population densities tend to vary with seasons. Their mobility also depends on the availability of food, so animals go away if there are no food in the area.
Plants on the other hand don't move around faster (they can migrate by reproduction: it's their seeds moving around). Thus their densities tend to be more constant per season/life cycle.
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Basically because your skin has several layers to it (see link, below), and the layer that has the blood vessels capable of bleeding in it is further down than a superficial scrape would affect.
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A cell membrane has consists of phospholipids. They are lipids with a phosphate group such as (PO3/4). They are hydrophilic meaning that they allow water to pass through proteins well some at least- but it might be needed to move molecules throughnthe membrane as well. But basically it's just a composed bilayer of phospholipids with hydrophobic acid tails so that they could all meet with one another. The form complexes into function to describe or to identify the cells to anothers cells.
Hope this helps.
The cytoskeleton of a cell allows the cell to be flexible. Our human skeletons allow <em>us </em>to be flexible.
Answer:
The allele frequency changed
The light moths blended in with the light-colored trees. However, the Industrial Revolution changed the tree colors. After the pollution from the Industrial Revolution started affecting trees, most of the collected peppered moths were of the dark form.
