Lesson 3 - Levels of Organization of the Human Body
Student Performance Objectives
1. Draw a diagram illustrating levels of organization in the human body including one specific
example at each level.
2. List and explain 5 characteristics of life unique to living systems and 5 life characteristics
shared with non-living systems.
3. Explain the significance of the statement, "Life is composed of lifeless molecules" and
explain why the cellular level of organization is so significant.
4. Explain the saying "seeing is believing" considering the size of living cells, the limits of
human vision, and the significance of the development of the light and electron microscopes.
A. The major levels from Higher to Lower
1. Organism - this, for example, is you, or a cat or rat, or any independent biological entity.
2. Organ systems - there are 11 organ systems in the human body. Can you list them as you did in the previous lesson?
3. Organs - the stomach and small intestine are two organs within the Digestive System. List and review the major organs in each of the body's 11 organ systems.
4. Tissues - The 4 basic tissue types are epithelial, connective, muscular and nervous.
a. Epithelial tissues form linings, like the lining of your mouth that you can feel with your tongue, and membranes, like the mesentery that helps to suspend the small intestine in place in your abdominal cavity. Epithelial tissues also form coverings like the outer layer of the body - the epidermis, or upper layer of the skin.
b. Connective tissues hold other tissues together such as loose, or areolar, connective tissue holds the lining of your mouth to underlying tissues. Ligaments hold bones together at joints and tendons bind muscle tissue to bone at the bone's surface.
c. Muscular tissues cause movements through contraction and relaxation. The voluntary movements of your body are through skeletal muscles; the walls of your internal organs, like the stomach, are composed of smooth muscles; and your heart is composed of cardiac muscle.
d. Nervous tissues send signals from one location to another resulting in the control and coordination of bodily activities. The brain and spinal cord are composed in part of nervous tissue; a great part of the brain and spinal cord are composed of specialized neural connective tissue that supports, nourishes and protects the nervous tissue.
5. Cells - these are the smallest units within us that possess the characteristics of life. They cannot be seen with the naked eye and require the use of a microscope. Each tissue type is composed of cells: e.g., epithelial tissues are composed of epithelial cells. Each major cell type has different varieties: e.g., epithelial cells can be flat like tiles on a floor and are called squamous epithelial cells. Cells will be considered in more detail in a later lesson.
6. Organelles - "little organs." Represent the division of labor within cells.
7. Macromolecules - The 4 basic types are carbohydrates, lipids, proteins and nucleic acids. The macromolecules are arranged to form the organelles composing cells.
8. Molecules - the smallest unit of a compound; composed of 2 or more atoms. E.g., the smallest unit of water is a water molecule. A drop of water would contain trillions of water molecules.
9. Atoms - the smallest unit of an element. Elements are the simplest substances in nature. The periodic table that you learned about in chemistry is a listing of the known elements in nature. E.g., an atom of oxygen is just one "O". But oxygen gas that we breathe from the air is O2, which is 2 atoms of oxygen bonded together.
10. Subatomic particles - the most well understood are the protons, neutrons and electrons.
B. Distinguish level where "life" begins - we say it is at the cellular level. We do not have an exact definition of life - we list characteristics that we find in living things.
1. Unique characteristics of living things: composed of cells and DNA, reproduce, self-maintain, self defend, grow and evolve.
2. Other characteristics of living things shared with non-living objects: move, have some type of metabolism.
C. Distinguish level first visible with the naked eye: a ovulated, human ovum is 100 u (100 microns)- and can be seen as a pinpoint; blood as a tissue can be seen; but the organ level is the first level of organization that can be seen in detail with the naked eye.
1. Use of optical aids
a. Simple microscopes - basically powerful magnifying glasses.
b. Compound microscopes of different types: brightfield, which are the type used in your laboratory classes; phase microscopes are available for your to observe at the instructor's desk - phase microscopes make use of the differences in the density of different parts of a cells and tissues and permits their visualization with staining them. Staining cells and tissues kills them; using phase microscopes allows often clear visualization of living cells and tissues.
c. Electron microscope: transmission, scanning and tunneling electron microscopes.
2. Exceptional situations, as mentioned: visibility of the human egg with the naked eye; what level of
organization is blood?