Question

Cluster or group of cells is known as
A. Tissue
B. Organ
C. Organism
D. None of the above

Answer 1

Hint: A cell is the structural as well as functional unit of life. All living organisms are composed of various types of cells to bring about different significant functions for the body. For survival, even a single cell requires a source for energy. In general, glucose serves as a common energy source for all cells.

Complete answer:
The group of cells that perform a similar type of function generally forms a tissue. These cells have their common specialized structure and often perform their function while coordinating among themselves. Hence, a group of similar types of cells having common function is referred to as a tissue. There are four basic types of tissues (nervous tissues, epithelial tissues, muscle tissues and connective tissues) that are found in humans and other large multicellular animals.
When two or more tissues are organized together to perform a particular function, then the resulting structure is called an organ. These tissues usually perform a specific set of bodily functions within an organ. Different organs having related functions collectively form an organ system. However, different organ systems are composed within an organism.

The correct answer is option A, tissue.

Note:
The body of complex multicellular organisms has different levels of organization including the cell (being at the lowest one), tissue, organ, organ system, and organism. A group of cells form tissue, a group of tissues form an organ, a group of organs forms an organ system, a group of organ systems gives rise to an organism. Unlike multicellular organisms, the unicellular organisms (such as amoeba) are made up of a single cell only.