Levels of Organization & Characteristics of Life

Levels of Organization –

The human body is the sum of its parts and these parts can be studied at a variety of levels of organization.

1. Atoms are the simplest level (H+).

2. Two or more atoms comprise a molecule (H2).

3. Macromolecules are large, biologically important molecules inside cells (enzyme).

4. Organelles are aggregates of macromolecules used to carry out a specific function in the cell (mitochondria).

5. Cells are the basic living unit.

6. Tissues are groups of cells functioning together.

7. Groups of tissues form organs.

8. Groups of organs function together as organ systems.

9. Organ systems functioning together make up an organism.

Fundamental characteristics of life are traits shared by all organisms.

Characteristics of life include:

1. Movement (internal or gross)

2. Responsiveness (reaction to internal or external change)

3. Growth (increase in size without change in shape)

4. Reproduction (new organisms or new cells)

5. Respiration (use of oxygen; removal of CO₂)

6. Digestion (breakdown of food into simpler forms)

7. Absorption (movement of substances through membranes and into fluids)

8. Circulation (movement within body fluids)

9. Assimilation (changing nutrients into chemically different forms)

10. Excretion (removal of metabolic wastes)

The total of all the chemical reactions occurring within the body to maintain these characteristics constitutes metabolism.

A. Requirements of Organisms

1. Life depends on the availability of the following:

a. Water (required for metabolic reactions, for transport of substances, and temperature regulation)

b. Food (nutrients needed to supply energy and raw materials for building new living matter)

c. Oxygen (used in releasing energy from nutrients)

d. Heat (a byproduct of metabolism; its presence governs the rate at which reactions occur)

e. Pressure (force required to facilitate movement of air or fluids)

Both the quality and quantity of these factors are important.