Biological organization in living organisms begins at the cellular level. The cellular level is the fundamental unit of life and is where all the essential functions and activities of living organisms occur. Let's explore this concept in more detail.

1. Cellular Level:
At the cellular level, living organisms are composed of cells, which are the basic building blocks of life. Cells are highly specialized and carry out specific functions necessary for the survival and functioning of the organism. They can be either prokaryotic (lacking a nucleus) or eukaryotic (containing a nucleus).
- Prokaryotic cells are found in bacteria and archaea, while eukaryotic cells are found in plants, animals, fungi, and protists.
- Within cells, various organelles such as the nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus perform specific functions to maintain the cell's integrity and support its activities.

2. Tissue Level:
Cells with similar structure and function come together to form tissues. Tissues are groups of cells that work together to perform specific functions. There are four primary types of tissues in multicellular organisms:
- Epithelial tissue: covers and protects body surfaces and lines organs and cavities.
- Connective tissue: provides support, connects, and protects different structures of the body.
- Muscle tissue: responsible for movement and contraction.
- Nervous tissue: transmits and processes information, enabling coordination and control.

3. Organ Level:
Different tissues combine to form organs. Organs are structures composed of two or more tissues that work together to perform specific functions. Examples of organs in the human body include the heart, lungs, liver, and brain. Each organ has a specialized structure and function that contributes to the overall functioning of the organism.

4. Organ System Level:
Organs with related functions are organized into organ systems. Organ systems are groups of organs that work together to perform specific physiological functions. Examples of organ systems include the respiratory system, circulatory system, digestive system, and nervous system. Each organ system contributes to the overall homeostasis and survival of the organism.

In conclusion, biological organization in living organisms begins at the cellular level and progresses to higher levels of organization, including tissues, organs, and organ systems. Understanding the hierarchical organization of living organisms is crucial to comprehend their structure, function, and interactions.