The type of tissue whose major function is for cells to shorten is muscle tissue.

Here's why:

* Muscle cells are specialized to contract, which means they can shorten in length. This shortening is what allows muscles to generate force and movement.

* There are three types of muscle tissue:

* Skeletal muscle: Attached to bones, responsible for voluntary movement.

* Smooth muscle: Found in the walls of internal organs, responsible for involuntary movements like digestion.

* Cardiac muscle: Found in the heart, responsible for pumping blood.

Let me know if you'd like more information on any of these muscle tissue types!