A tissue is a

Options

A. group of separate organs that are coordinated in their activities
B. group of similar cells that function together to perform an activity
C. layer of cells surrounding an organ
D. sheet of cells one layer thick

Answer

### Step-by-Step Solution:

1. **Definition of Tissue**: A tissue is defined as a group of similar cells that work together to perform a specific function. This is the fundamental concept of what constitutes a tissue.

2. **Types of Tissues**: There are various types of tissues in biological organisms. For example, muscular tissue (which helps in movement), nervous tissue (which is involved in transmitting signals), skeletal tissue (which provides structure), and cardiac tissue (which makes up the heart).

3. **Distinction from Organ Systems**: It is important to differentiate between tissues and organ systems. An organ system is a group of different organs that work together to perform complex functions. For example, the nervous system and circulatory system are made up of multiple organs working in coordination.

4. **Hierarchy of Biological Organization**: Tissues are part of a larger hierarchy in biological organization. Similar cells form tissues, tissues combine to form organs, and organs work together to form organ systems.

5. **Conclusion**: Therefore, the correct definition of a tissue is that it is a group of similar cells that function together to perform a specific activity.