The organelles and substances inside the organelles are smaller. On a molecular level a group that are smaller are hadrons, which are the group of particles that consist of protons and neutrons. Even smaller than hadrons are leptons, which consist of neutrinos, electons, and MANY others.
JJ Thompson discovered subatomic particles, focusing mainly on the electron
A) A flap in the heart located between each atrium and ventricle.
Hope it helps! :)