The Cell The cell is one of the most basic units of life. There are millions of different types of cells. There are cells that are organisms onto themselves, such as microscopic amoeba and bacteria cells. There are cells that only function when part of a larger organism, such as the cells that make up your body.

The one- celled organism amoeba proteus

A single- celled bacteria of the type: E. coli

A plant cell from the leaf of a poplar tree

A human red blood cell

The cell is the smallest unit of life in our bodies. In the body, there are brain cells, skin cells, liver cells, stomach cells, and the list goes on. All of these cells have unique functions and features.

Staphylococcus aureus Cell division in this bacteria can occur every 20 to 30 minutes.

Leukemia Cell This leukemia cell is tearing itself apart

Fibrin Clot with Red Cells Platelets released from the circulation and exposed to the air use fibrinogen from the blood plasma to spin a mesh of fibrin

Escherichia coli Escherichia coli (E. coli ) are very common intestinal inhabitants. Some can be dangerous in food and water supplies

Human Macrophage Human macrophage ingesting Streptococcus pyogenes. The spherical cell riding piggy-back on the macrophage is a lymphocyte, an important component in the immune response to infection

Human Red Blood Cells Red cells get their red color from iron-rich hemoglobin which is responsible for transporting oxygen throughout the body

Human Neutrophil Human neutrophils are white blood cells that serve as professional phagocytes: their primary function is to eat and kill bacteria and they arrive quickly at the site of a bacterial infection

Human Eosinophil Eosinophils are important in combatting parasitic diseases

There are many different types of cells in the human body. None of these cells function well on there own, they are part of the larger organism that is called - you.

Tissues Cells group together in the body to form tissues - a collection of similar cells that group together to perform a specialized function. There are 4 primary tissue types in the human body: epithelial tissue, connective tissue, muscle tissue and nerve tissue.

Epithelial tissue serve as membranes lining organs and helping to keep the body's organs separate, in place and protected. Some examples of epithelial tissue are: outer layer of the skin inside of the mouth stomach tissue surrounding the body's organs.

Most types of connective tissue contain fibrous strands of the protein collagen that add strength to connective tissue. Some examples of connective tissue include: inner layers of skin, tendons, ligaments, cartilage, bone and fat tissue.

Muscle tissue is a specialized tissue that can contract. Muscle tissue contains the specialized proteins actin and myosin that slide past one another and allow movement. Examples of muscle tissue are contained in the muscles throughout your body

Nerve tissue has the ability to generate and conduct electrical signals in the body. These electrical messages are managed by nerve tissue in the brain and transmitted down the spinal cord to the body

An organ is a structure that contains at least two different types of tissue functioning together for a common purpose. There are many different organs in the body: liver, kidneys, heart, even your skin is an organ. In fact, the skin is the largest organ in the human body

The skin is composed of three layers: the epidermis, dermis and subcutaneous layer. The epidermis consists of epithelial tissue. Below the epidermis lies a layer of connective tissue called the dermis. The dermis contains blood vessels that nourish skin cells. It contains nerve tissue that provides feeling in the skin. And it contains muscle tissue that is responsible for giving you 'goosebumps' when you get cold or frightened. The subcutaneous layer is beneath the dermis and consists mainly of a type of connective tissue called adipose tissue. Adipose tissue is more commonly known as fat

Organ systems are composed of two or more different organs that work together to provide a common function. There are 11 major organ systems in the human body

The main role of the skeletal system is to: provide support for the body protect delicate internal organs provide attachment sites for the organs.

The main role of the muscular system is to provide movement. Muscles work in pairs to move limbs and provide the organism with mobility. Muscles also control the movement of materials through some organs, such as the stomach and intestine, and the heart and circulatory system