A new development involves a network of plastic tubes being printed within an organ. After the whole organ is printed, these plastic tubes are dissolved, leaving a network of empty tunnels. Why does the organ need to have the empty tunnels within it?

These are needed to mimic the blood vessels which these organs will use for the supply or drainage of fluids e.g blood.

In addition the empty tunnels serve as the routes for nutrients and oxygen supply  for the organ.

In summary the tunnels provided  a vascular structure to support the organ

Explanation:

answer: tributaries flow into rivers.

wetland is a biome that develops when the water gets accumulated in a land exhibiting a huge depression. these form either seasonally or permanently. the water in the wetland comes from rivers, lakes, ocean, flood, rain or other sources. the wetlands includes mangroves, marshes and peatland.

tributaries flow into the rivers develops a wetland because such water will get deposited in the depression and will restrict the original flow of tributary water. hence, water with low drainage current combines with the river water.

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