When many cells share similar structural markers, adhere to one another, and work together to perform a specific function, what level of organisation do they form in the body?

Introduction / Context:
Biology describes life using a hierarchy of structural organisation, from individual cells up to whole organisms and ecosystems. Understanding the intermediate levels helps to make sense of how complex bodies are built from simpler units. This question focuses on what happens when similar cells with shared properties and markers stick together and carry out a common function as a group.

Given Data / Assumptions:

• The cells mentioned share similar markers and characteristics.
• These cells adhere to each other and function together.
• We are choosing the correct level of biological organisation based on this description.

Concept / Approach:
The standard levels of structural organisation in multicellular organisms are: cells → tissues → organs → organ systems → organism. A tissue is defined as a group of similar cells that work together to perform a specific function, such as muscle contraction or signal conduction. For example, cardiac muscle tissue consists of cardiac muscle cells working together to pump blood. Organs consist of several different tissue types combined to perform a more complex function, such as the heart or lungs. Organ systems combine multiple organs. Therefore, when the question describes similar cells sticking together and functioning as a unit, it is describing a tissue.

Step-by-Step Solution:
Step 1: Recall that individual cells are the basic structural and functional units of life. Step 2: Recognise that the next level above a single cell is a tissue, which is made of similar cells with a common function. Step 3: Understand that organs are built from more than one type of tissue working together, not just from similar cells. Step 4: Select tissues as the level of organisation that best matches “similar cells that stick together and function as a unit”.

Verification / Alternative check:
Textbooks list four basic tissue types in animals: epithelial, connective, muscle, and nervous tissue. Each tissue is made of cells that share particular markers and functions, such as contractile proteins in muscle cells or electrical excitability in nerve cells. Organs such as the heart contain several of these tissues, for example cardiac muscle tissue, connective tissue, and nervous tissue. This confirms that the question's description corresponds to tissues, not to organs or higher levels.

Why Other Options Are Wrong:

• Organs: Organs are made up of different types of tissues combined, rather than just similar cells alone.
• Organ systems: These are groups of organs working together, such as the digestive system or respiratory system.
• Complete organisms: An organism contains many organ systems and is the highest level of structural organisation in this list.

Common Pitfalls:
Students sometimes confuse tissues and organs because both involve multiple cells. A helpful way to remember the difference is that tissues are groups of similar cells, while organs are groups of different tissues. For example, skeletal muscle tissue is one type of tissue; your biceps muscle as a whole is an organ made largely of that tissue plus supporting tissues. Keeping the hierarchy in mind prevents mixing up these terms in exam questions.

Final Answer:
Cells with similar markers that stick together and work as a unit form a tissue in the body.