Levels of Organization

Levels of Organization

  • There are 6 levels of organization in complex organisms.

    • From smallest to largest:

    • Cell

    • Tissue

    • Organ

    • Organ System

    • Organism

Cells

  • The most basic unit of structure and function of all living things.

  • Cells are extremely small and require the use of a microscope in order to view them.

  • Robert Hooke – credited with the discovery of the cell.

  • Anton van Leeuwenhoek – first person to observe living cells.

Examples of Cells

  • Red blood cells

  • Neurons (nerve cells)

  • Epithelial cells

Tissues

  • Groups of similar cells performing the same function.

Examples of Tissues

  • Connective tissue – connects, supports, or surrounds other tissues or organs.

  • Epithelial tissue – covers body surfaces, body cavities, and organs.

  • Muscle tissue – composed of muscle cells that can contract to produce movement.

  • Nervous tissue – composed of cells that receive stimuli and conduct impulses in the body.

Organs

  • A group of tissues that work together to perform a specific function.

  • There are 78 organs in the human body.

  • 5 vital organs – brain, heart, kidneys, liver, and lungs.

Examples of Organs

  • Heart

  • Kidney

  • Liver

Organ Systems

  • A group of organs that work together to perform a specific function.

  • There are 11 organ systems in the human body.

Examples of Organ Systems

  • Circulatory system

  • Digestive system

  • Nervous system

Organisms

  • A living individual that can reproduce, grow, and maintain homeostasis.

  • Can belong to any of the 6 kingdoms of life.

  • Scientists estimate there are about 8.7 million species of organisms on Earth.

Examples of Organisms

  • Humans

  • Dogs

  • Trees

Cell Theory

  • Developed by German scientists Matthias Schleiden, Theodor Schwann, and Rudolf Virchow.

3 Parts of Cell Theory

  • Cells are the basic unit of life.

  • All living things are made up of one or more cells.

  • New cells come from existing living cells.

Checkpoint Questions

Question 1:

  • What would happen if a large majority of an organism’s cells suddenly became diseased and died?

Question 2:

  • Which organ in the human body do you think is the most important? Explain.

Question 3:

  • Identify 3 organ systems located in the human body.

Question 4:

  • List the levels of organization from smallest to largest.

Question 5:

  • Describe the 3 parts of cell theory in your own words.