They are called negative pressure rooms because the air pressure inside the room is lower than the air pressure outside the room. This means that when the door is opened, potentially contaminated air or other dangerous particles from inside the room will not flow outside into non-contaminated areas.

Cells in vascular tissue Vascular tissue in plants is made of two specialized conducting tissues: xylem, which conducts water, and phloem, which conducts sugars and other organic compounds.

The xylem is specialised to transport water up the stem of a plant and into the leaves. A substance called lignin strengthens the cell walls of xylem cells. Phloem cells. The phloem is specialised to transport food products to parts of the plant where they are needed.

Xylem tissue is used mostly for transporting water from roots to stems and leaves but also transports other dissolved compounds. Phloem is responsible for transporting food produced from photosynthesis from leaves to non-photosynthesizing parts of a plant such as roots and stems.

A: Negative pressure generally refers a place where pressure is smaller in one place relative to another place. That means the air pressure inside the room is lower than the pressure outside the room and air will flow into the room from outside.

You can absolutely have negative absolute pressure in solids or liquids. Think of an elastic solid being forced to expand due to adhesion to the walls of some chamber. That has negative pressure even if the comparison is a total vacuum.

Since the value of the vacuum is below the reference pressure, it is also called negative pressure. For example, if you suck in air with a fan, it creates air suction that can cause negative pressure.