Which device use electromagnets?

Explanation:

Motors and generators.

Transformers.

Relays.

Electric bells and buzzers.

Loudspeakers and headphones.

Actuators such as valves.

Magnetic recording and data storage equipment: tape recorders, VCRs, hard disks.

MRI machines.

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