Schleiden and Schwann believed that cells are the basic unit of organisms including plants and animals. They don't believed that organisms are the basic unit of life nor the cells and organisms are. They also don't see the issue on the basic unit of life as vague.
Both of them have made their own innovations and achievements but collectively they have made one very important discovery (1839): "The Theory of Cells". This theory badges the cell as a basic particle of plants and animals. Schwann and Schleiden were capable to understand that some organism is unicellular, while others are multicellular. Additionally, they found out that the cell nucleus and the membrane refer to the properties of the cell, maintained by representations of various plant and animal tissues.
<span>NA contains only elements, so it does not react easily. Many organisms do not contain DNA. Certain mutations in DNA happen at a constant rate. DNA does not change over time, making it a valuable clue.</span>
