The cell is the smallest unit of life. The cell was culled from Latin word called cella, which means “small room.” It represents the organic, functional and structural unity of every living organism and it forms the basis on which the fundamentals of biology is built. They are also referred to as the building blocks of life. Cells are made up of a cytoplasm covered by a cell membrane, and the cell membrane is made up of many biomolecules like nucleic acids and proteins. Some organisms are unicellular, while some other ones are multicellular. The unicellular has just one cell, while the multicellular organisms have multiple cells. Good examples of unicellular organisms are bacteria, while plants and animals represent multicellular organisms. There are numerous plants and animals around, and each of them varies in the number of cells they have as constituents. In human beings, for example, there are up to 10 trillion cells. Most of the cells in plants and animals can be viewed easily using light microscope since their size is between 1 and 100 micrometers.

Cellular levels
The smallest unit in cellular level is the atom, which is composed of elements, like nitrogen, carbon, and hydrogen.

This is followed by Molecule, which is composed of molecular structures, like amino acids, glucose, fatty acid and the likes.

Molecules are a combination of atoms. Molecules, on the other hand, combine together to form macromolecules, and a good example of this are the DNA. Macromolecules combine to form organelles, a good example of which is the nucleus. Others are mitochondria, ribosome, cell membranes, lysosome and so on, with each of these organelles playing specific roles in the structure and functions of the living cell and the organism.

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Group of organelles combines to form the cell, and there are different forms of cells. Good examples are the nerve cells, which is located in the brain and spinal cord and only found in animals. Conclusively, atoms, molecules, macromolecules, organelles and cells combine to make up the cellular level of life.

Organism level
Cells combine to form what is called tissue, and a good example of tissue is the nerve tissue. Others are connective tissues, epithelial tissue, and muscular tissue. These four types of tissue form the main types available in living things, especially animals. Tissues combine to form organs. There are various types of organs in the body, and good examples of organs are brain, eyes, liver, heart, kidney and many others. Organs work together to form systems. Magnificent examples of organ systems are nervous system, which involves various organs, like the brain. The eyes are classified as an extension of the human brain. Other systems are the respiratory system, involving the nose, the lungs, and even the heart. There is also the reproductive system, the digestive system, with each playing its specific role to ensure physiological balance in animals. The organ systems combine to form the organism, like birds, man, lion and so on.

Would you like to read more about this topic? This book might interest you: Biology Fundamentals.