In the Endosymbiotic Theory for the origin of eukaryotes, the final step was the engulfing a functional cyanobacterium to produce photosynthetic eukaryotes ("plants"). Why is this stage considered the final step in the sequence of eukaryote evolution?

The Endosymbiotic Theory of eukaryote evolution is known as Symbiogenesis that states the evolution of eukaryotic cells from prokaryotic organisms.

The engulfing a functional cyanobacterium to produce photosynthetic eukaryotes ("plants") is considered as final step of the eukaryote evolution because a functional cyanobacterium closely resemble the chloroplast and related to mitochondria and it maintains a large genome that encodes thousands of proteins.

A photosynthetic eukaryotes ("plants") require cholorplast (green pigment) for photosynthesis and protein synthesis, which all are provided by functional cyanobacterium, after that a eukaryote can functions as an individual eukaryote and not as prokaryote, and hence engulfing functional cyanobacterium is considered as last step of eukaryote evolution.

answer:

the water molecules are transferred from the roots to the stem or top parts of the tall tree because of important properties of water which are adhesion, cohesion and capillary action. cohesion is the property of water molecules keeps water molecules in a combined state by sharing of bonds between them at the atomic level. adhesion allows the interaction of water molecules with other substances or substrate. adhesion will cause the attachment of water molecules to the wall of the vessel (xylem) of the plant. capillary action occurs when the adhesive force to the vessel wall is stronger than the cohesive force between water molecules. capillary action mimics the transfer of water from a tube or pipe. in this way water utilizes its property to transfer water from down to top level of the plant.