Final answer:
A single sarcomere does not contain a complete, continuous I band. Instead, it includes two halves of an I band, one on each side of the A band, with the Z line bisecting them. The I band shortens during muscle contraction.
Step-by-step explanation:
In skeletal muscle cells, the sarcomere is the basic unit of contraction, comprising a specific arrangement of protein filaments. Within each sarcomere, the I band is a region that contains only thin filaments (actin), which are anchored to the Z line, also known as the Z disc. This Z line demarcates the boundaries between adjacent sarcomeres. Each I band actually spans two sarcomeres, being bisected by a Z line. Therefore, a single sarcomere does not contain a complete, continuous I band; rather, it includes half of an I band on each side of the A band, which contains both thick (myosin) and thin (actin) filaments and is centrally located. The A band remains the same width during muscle contraction, but the I band shortens as the sarcomere contracts with the Z lines moving closer together.