Use a model to explain the levels of biological organization and how organ systems interact to support the functions of a multicellular organism (Tennessee Academic Standards for Science, Biology I, BIO1.LS1).

What this topic is asking

The Tennessee LS1 standards ask you to model the levels of biological organization and explain how organ systems interact to keep a multicellular organism alive. For the Biology I EOC that means knowing the order from cell up to organism, the major human organ systems and their jobs, and the crucial idea that the systems are interdependent, working together rather than alone. Items often ask you to order the levels or to explain how two systems cooperate during an activity.

The levels of organization

This sequence builds on cell theory: because the cell is the basic unit, every higher level is ultimately built from cells. EOC items frequently ask you to put these levels in order (and sometimes include the lower chemical levels of atoms and molecules, which combine to form cells).

The major organ systems and their jobs

The Biology I course surveys the human organ systems as examples of structure and function. The ones the EOC most often references:

• Circulatory system. Transports oxygen, nutrients, hormones, and wastes around the body (heart, blood vessels, blood).
• Respiratory system. Brings in oxygen and removes carbon dioxide (lungs, airways).
• Digestive system. Breaks down food and absorbs nutrients (stomach, intestines).
• Nervous system. Detects stimuli and coordinates fast responses (brain, spinal cord, nerves).
• Endocrine system. Uses hormones for slower, longer-lasting control (glands such as the pancreas).
• Immune system. Defends against pathogens.
• Muscular and skeletal systems. Provide movement and support.
• Excretory system. Removes wastes and helps balance water and salts (kidneys).

You do not need every organ, but you should know what each major system does and be able to pair a system with its function.

Systems work together

For example, exercise requires several systems at once: the respiratory system takes in oxygen, the circulatory system delivers that oxygen and glucose to the muscular system, the nervous system coordinates the movements, and the excretory system removes the wastes produced. This cooperation is the point of the standard: the body is a system of systems, and homeostasis depends on them communicating and coordinating.

Try this

Q1. List the levels of organization from smallest to largest. [2]

• Cue. Cell, tissue, organ, organ system, organism.

Q2. Name two organ systems and state what each contributes when a person is running. [2]

• Cue. Any two with correct jobs, for example respiratory (takes in oxygen, removes carbon dioxide) and circulatory (transports oxygen and glucose to muscles); muscular (moves the body) is also acceptable.