Kelp (a kind of seaweed)
About 600 million years ago, the first plant cells evolved to be different from animal cells, and from earlier prokaryote cells, because they had a stiff cell wall made of molecules of carbon and oxygen, with some other elements like hydrogen, nitrogen, and calcium as well.
In plants, the part that corresponds to our bones and the part that corresponds to our blood vessels are the same thing: the vascular system. The earliest plants, and most plants still living on the Earth today, don't have any sort of vascular system, because they only have one cell and they don't need any support or food supply. Even some plants with many cells, like seaweed, don't need support because they float in the ocean. But some seaweed does have a way to transport water from one cell to another. The earliest land plants, like moss, also didn't have any support structure, though they do have some.
To find out more about plants, check out these books from Amazon.com or from your library:
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