Phase transitions in biological systems

image from http://www.chemistry.wustl.edu/%7Ecourses/genchem/LabTutorials/Thermochem/images/PhaseChanges.jpg

Phase transitions are present everywhere. Even within something as complex as the human body or plants, phase transitions are still present throughout processes which these systems use to survive. Critical phenomena such as second-order phase transitions are hard to find in certain biological systems however first-order phase transitions are easily present. Trying to analyze a biological system to define that phase transitions that occur within the system can sometimes be difficult but they are there.

Biological Materials as Soft Condensed Matter?

Why yes! Many biological materials can be considered to be soft condensed matter. Believe it or not, but muscles and blood exhibit properties which allows them to be classified as soft condensed matter. Blood can be classified as a colloid, which is a chemical substance consisting of a mix of various things. The various things that make up a colloid are not dissolved in it, but rather are distributive evenly within the substance. The neat thing about colloids is that they're able to exist in gaseous, liquid, and solids forms.

The Human Body as a Biological System

The human body is a very complex biological system with many organ systems within itself that allow bodily process to maintain life. Within these systems, various phase transitions do occur. Many of these phase transitions are necessary in order for things to work.

Respiratory System

Respiration itself requires many phase transitions. It begins simply with the inhalation of O₂ gas which enters the lungs. Inhalation is done by stimulation of pulmonary muscles which allows the diaphragm to contract, allowing oxygen to enter the lungs. Oxygen gas gets absorbed into the bloodstream through little compartments that make up the lungs known as alveoli by way of diffusion. The oxygen gas binds to a solid protein known as hemoglobin, and is then carried throughout the body in blood, which in can be considered a liquid. In term of phase transitioning, the oxygen gas diffuses into liquid blood and remains there by way of binding to a solid protein. At the same time, carbon dioxide gas (CO₂)is also moving through the blood stream where it will diffuse into the lungs and out of the body by exhalation.

image from Brittanica 2006

Digestive System

Breakdown of food for energy. ATP.

Circulatory System

Transportation

Nervous System

Various signaling pathways

Reproductive System

The fertilization of an egg by sperm is irreversible.

Plants as a Biological System

Photosynthesis

Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com)

Biological Thermodynamics

Biological Thermodynamics combines the laws of thermodynamics with biology in order to explain or possibly quantify changes in energy from reactions. Many organ systems within the human body, (if not all of them), require some energy in order to function. In a plant, photosynthesis converts sunlight to energy usable by the plant so that it may synthesize sugars out of carbon dioxide gas and water. There has to be some sort of method to quantify the energy required in these reactions.