Tissue culture experiments with pdgf demonstrate that without this substance
1. bacterial cells lose their resistance to antibiotics
2. fibroblasts fail to divide
3. animal cells are unable to attach to the substratum
4. cells divide in an uncontrolled fashion, confirming its role as a cell division inhibitor
5. the various kinases, such as mpf, are unable to bind to cyclin

Answer is 2. Fibroblasts fail to divide.

Explanation:

Tissue culture experiment is the experiment where tissues are grown in an artificial medium. This involves the use of growth medium such as agar or broth. This process help to produce needed tissues in a short period of time.

Fibroblasts are cells which are found in the collective tissues, and they produce collagen. The collagen produced by the Fibroblasts play important role in tissue repair. Fibroblasts are regarded as the main cells in the connective tissue.

Note that, PDGF, which is Platelet -derived growth factor in full, is a growth factor regulating cell growth and it's division.

a physical change is being made.