Levels of Organization
Unit 2: The Chemistry of Water
Unit outline
Part 1. Biological importance of water
- Water as a Lubricant and Cushion
- Water as a Heat Sink
- Water as a Component of Liquid Mixtures
- The Role of Water in Chemical Reactions
Part 2. Fluid compartments in the human body
- Body Water Content
- Fluid Compartments
- Intracellular Fluid
- Extracellular Fluid
Practice Questions
Learning Objectives
At the end of this unit, you should be able to:
I. Explain the biological importance of water.
II. Specify the percentage of body weight that is composed of water and estimate the amount of body water you contain in litres.
III. Describe the distribution of body water.
Learning Objectives and Guiding Questions
At the end of this unit, you should be able to complete all the following tasks, including answering the guiding questions associated with each task.
I. Explain the biological importance of water.
- For each of the four biologically important properties of water:
- Identify the property.
- Describe its importance in the human body.
II. Specify the percentage of body weight that is composed of water and estimate the amount of body water you contain in litres.
- Given your (approximate) body weight, calculate the amount of water you contain, in litres. You may use a calculator if necessary, but must clearly show all your work!
III. Describe the distribution of body water.
- For each of the major fluid compartments of the human body:
- Name the compartment.
- Define the compartment by specifying its location in the human body.
- Specify the percentage of body fluid volume made up by that compartment.
As much as 70 percent of a human’s body weight is water. This water is contained both within the cells and between the cells that make up tissues and organs. Its several roles make water indispensable to human functioning.
Part 1. Biological Importance of Water
Water as a Lubricant and Cushion
Water is a major component of many of the body’s lubricating fluids. Just as oil lubricates the hinge on a door, water in synovial fluid lubricates the actions of body joints, and water in pleural fluid helps the lungs expand and recoil with breathing. Watery fluids help keep food flowing through the digestive tract, and ensure that the movement of adjacent abdominal organs is friction free.
Water also protects cells and organs from physical trauma, cushioning the brain within the skull, for example, and protecting the delicate nerve tissue of the eyes. Water cushions a developing fetus in the mother’s womb as well.
Water as a Heat Sink
A heat sink is a substance or object that absorbs and dissipates heat but does not experience a corresponding increase in temperature. In the body, water absorbs the heat generated by chemical reactions without greatly increasing in temperature. Moreover, when environmental temperature soars, the water stored in the body helps keep the body cool. This cooling effect happens as warm blood from the body’s core flows t