What is the smallest part of an element that still has the properties of said element?

The smallest particle of an element that can exist is an atom

The smallest particle of an element that can exist is called an atom. John Dalton first proposed this in 1807. Today sophisticated instrumentation can take pictures of single atoms and nuclear physics has identified particles (forces) that make up the subatomic particles (protons, electrons, and neutrons). :P (hope i helped)

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Mitochondria is the cell organelle that produced the energy that is needed in the body system in form of atp, that is why it is called the power house of the cell. energy is needed by the living organisms to carry out the activities which sustain life.  if the mitochondria is destroyed atp will not be produced. if the mitochondria is destroyed, energy production will stop and the affected living organism will not have the energy to carry out the necessary life processes; this will lead to the death of the organism.