Agroup of similar cells that perform a particular function is called

Tissue

Explanation:

Tissue is a group of similar cells that work together to serve a common function. Tissues that work together are grouped and called organs which futher makes up a system. The digestive system for instance is made of different organs such as intestine, stomach which works together to digest food.

Each digestive organ in the digestive system has its own unique tissues, with each tissue having its own unique cells.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.