Question

Why does the solvent move upward in thin layer chromatography

Answer 1

The paper has capillaries in its fibers.

Answer 2

Here are two web sites. The first describes thin layer chromatography; the second describes paper chromatography. The medium for TLC is SiO2; the medium for paper chromatography is, of course, paper.
http://orgchem.colorado.edu/hndbksupport/TLC/TLC.html

http://en.wikipedia.org/wiki/Paper_chromatography