Actions that are reactions to a stimulus are called

The answer is reflex actions.

A reflex action is an involuntary and rapid reaction to a stimulus. So, when a receptor detects a stimulus, the information is sent to relay neuron through a sensory neuron. Relay neuron sends information to the effector through a motor neuron and effector produces a response.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

oxygen = 21% of the atmosphere

nitrogen = 78%

carbon dioxide = 0.1%

argon =0.934%