1. All living things are made up of cells.
2. Cells are the basic building blocks of life.
3. All cells come from preexisting cells created through the process of cell division.
As science evolved, three more components were added to the theory. Some biology classes don’t require you to know these parts of the cell theory because they weren’t part of the original definition, but it’s still useful to be aware of them:
4. Energy flow occurs within cells.
5. Hereditary information is passed from cell to cell.
6. All cells have the same basic chemical composition.
So what does the cell theory actually mean? Let’s break it down. The first part of the cell theory states that all living things are made up of cells. Anything that’s alive, from bacteria to plants to humans, is composed of cells. And what are cells? The literal definition is a cell is a group of organelles surrounded by a thin membrane.
The cell theory definition states that cells are the building blocks of life. Cells both make up all living things and run the processes needed for life. Your hair, skin, organs, etc. are all made up of cells. In fact, each person is estimated to be made up of nearly 40 trillion cells! Each part of a cell has a different function, and your cells are responsible for taking in nutrients, turning nutrients into energy, removing waste, and more. Basically, everything your body does, it does because cells are directing the action!
The third part of the cell theory definition states that all cells come from preexisting cells. This means that cells don’t just appear out of thin air (known as “spontaneous generation”). New cells are always made from current cells. This means that all current life on the planet is descended from the very first cells, which first made an appearance on Earth roughly 3.5 billion years ago. Cells have been replicating themselves continuously ever since.
And what does the newer part of the cell theory state? Part four refers to the fact that, in all living cells, energy is continuously transformed from one type to another. Examples of these processes include photosynthesis (where plant cells convert light energy into chemical energy) and cellular respiration (where both plant and animal cells convert glucose into energy). Part five refers to DNA and the fact it is passed from parent cell to child cell. Finally, part six of the cell theory tells us that all cells are made up of the same chemicals: water, inorganic ions, and organic molecules.
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