When did matthias schleiden contribute to the cell theory

1938

Explanation:

Matthias Schleiden was a German botanist who studied the plant's cell and its structure under the microscope. In 1938 he contributed to the cell theory and stated that every tissue present in the plant is made of or cells and an embryonic plant is produced from one single cell.

In 1939 another scientist Theodor Schwann proposed the same conclusion after studying animal cells and concluded that the basic unit of life is cell and every organism on earth is made up of one or more cells. Therefore Theodor Schwann and Matthias Schleiden have great contribution in cell theory.  

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.

answer; hydrologic cycle;