In chemistry and biology, units interact (<~>)with each other in a dynamic way rather than having a strictly  additive (or subtractive) relationship.  This infers a more give and take interaction.  The interaction also has context, including a given environment, soace and time.

In chemistry and biology, in a given environment, in space and time, one unit interacts in a dynamic way with another unit to form a new unit with unique characteristics.

In Chemistry

In chemistry, we are mostly dealing with the interaction of negative and positive forces.
At the simplest level. a single electron interacts with a single proton, in space and time, to form the hydrogen atom which has completely different and unique characteristics
The hydrogen atom as a result of the interaction aqquires a magnetic field and starts to spin (or precess) like a spinning top- representing a new and unique characteristic.

 The 1+ 1 = 1 equation is still applicable, since units are additive in the formation of a bigger whole , and the end point “whole” of the interaction is still greater than the parts. 

The “+” in the original equation throughout the common vein will be replaced by a variety of different bonding mechanisms between two units.  For example in human biology the vessels including the arteries, veins, and ducts will bond two or more organs. 

 See  The Common Vein and Bonds