Organs join to form a(n) that performs a major function.

Organs join to form an "Organism" that performs a major function.

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Enzyme make a hormone as a catalyst

Spontaneity tell us the direction of the reaction, but not how fast it goes. gibbs free energy brings together enthalpy, entropy and temperature in one easy formula. g = h - ts. and, finally the sign of delta g is always negative for a spontaneous reaction.