Atoms are known to join together to form the molecules that make up a cell. A cell is the smallest structural and functional unit of an organism and some organisms exist as single cells. Human beings are multicellular because they are composed of many different types of cells. A nerve cell is one of the types of cells in the human body and it has a structure suitable for conducting nerve impulses.
Within the nucleus are positively charged particles called protons and particles without charge are neutrons that are circling around the nucleus as negatively charged particles that are known as electrons. The number and arrangement of the protons, neutrons, and electrons determine the element which is distinguished by its atomic number which equals the number of protons in the nucleus.
An element may also be assigned a mass number that refers to the sum of the protons and neutrons in the nucleus. Atoms with the same atomic number but which have different mass numbers are isotopes of the same chemical element.
A tissue is a group of similar cells that perform particular functions and nervous tissue is composed of millions of nerve cells that transmit signals to all parts of the body
An organ consists of several types of tissues and each organ belongs to an organ system. The organs of an organ system work together to perform common purposes; for example, the brain works with the spinal cord to send commands to various body parts by utilizing the nerves. Organisms; for example, vegetation, animals, and humans are each a collection of organ systems.
The various areas of biological organization extend beyond the individual. All of the members of one species or groups of interbreeding organisms, in a particular area belong to a population. A tropical grassland may have a population of zebras, acacia trees, and humans. The interacting populations of the grasslands make up a community and the community of populations interacts with the physical environment to form an ecosystem all of which make up the biosphere.