Molecular biology concerns the molecular basis of biological activity between biomolecules in the various systems of a cell, including the interactions between DNA, RNA, and proteins and their biosynthesis, as well as the regulation of these interactions.

Writing in Nature in 1961, William Astbury described molecular biology as:

Cell biology (formerly called cytology, from the Greek κυτος, kytos, "vessel") is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life.

Cell biology explains the structure, organization of the organelles they contain, their physiological properties, metabolic processes, signaling pathways, life cycle, and interactions with their environment.

This is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells.

Knowing the components of cells and how cells work is fundamental to all biological sciences; it is also essential for research in bio-medical fields such as cancer, and other diseases.

Research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.

Genetics is the study of genes, genetic variation, and heredity in living organisms.

It is generally considered a field of biology, but intersects frequently with many other life sciences and is strongly linked with the study of information systems.

Ecology (from, "house", or "environment"; -λογία, "study of") is the scientific analysis and study of interactions among organisms and their environment.

It is an interdisciplinary field that includes biology, geography, and Earth science.

Ecology includes the study of interactions that organisms have with each other, other organisms, and with abiotic components of their environment.

Topics of interest to ecologists include the diversity, distribution, amount (biomass), and number (population) of particular organisms, as well as cooperation and competition between organisms, both within and among ecosystems.

Ecosystems are composed of dynamically interacting parts including organisms, the communities they make up, and the non-living components of their environment.

Ecosystem processes, such as primary production, pedogenesis, nutrient cycling, and various niche construction activities, regulate the flux of energy and matter through an environment.

These processes are sustained by organisms with specific life history traits, and the variety of organisms is called biodiversity.

Biodiversity, which refers to the varieties of species, genes, and ecosystems, enhances certain ecosystem services.

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, evolution, distribution, identification and taxonomy.

Modern biology is a vast and eclectic field, composed of many .

However, despite the broad scope of biology, there are certain unifying concepts within it that consolidate it into single, coherent field.

In general, biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation of new species.

It is also understood today that all organisms survive by consuming and transforming energy and by regulating their internal environment to maintain a stable and vital condition known as homeostasis.