A(n) is a group of organs that work together to perform a common function

Cell
Tissue
Organ
Organ system

Tissue

Tissues are groups of similar cells that have a common function. The four basic tissue types are epithelial, muscle, connective, and nervous tissue. Each tissue type has a characteristic role in the body:

Epithelium covers the body surface and lines body cavities.

Muscle provides movement.

Connective tissue supports and protects body organs.

Nervous tissue provides a means of rapid internal communication by transmitting electrical impulses.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.