A teacher writing to a confused student.
bacteria are microscopic (very tiny) organisms that are unicellular (made up of a single cell). One fundamental difference is that bacterial cells lack intracellular organelles, such as mitochondria, chloroplasts, and a nucleus, which are present in both animal cells and plant cells.
Answer:
He identified that diseases are caused by malfunctioning cells.
That all cells arise from pre-existing cells.
