Enzymes fit their substrate like a “lock & key”. What does this mean?

What feature of cell theory is best demonstrated in the image

Will mark you as ! keiko’s teacher was discussing the theory of endosymbiosis. she asked keiko to mark the organelles in the diagram that most closely resembled prokaryotes. which organelles should keiko mark? * the first image is the question and the second image is some information to you answer the !

Which of the following is a testable hypotheses?