| Free water vs Bound water in life | ||
|---|---|---|
| Free water | Bound water | |
| Fluidity | Most of the water in an organism is free to flow. | The minority of water in an organism is bound to organic matter by hydrogen bonds. It can't move freely. |
| Function | 1. Transport of nutrients and waste 2. Excellent solvent 3. Participate in biochemical reactions | It is a component of the cell structure |
| Associations | Free water and bound water can be transformed into each other in the organism. | |
The earliest life was born in the ocean, and no matter how it evolved, water has always been essential to life. The content of water in living organisms is generally 60% to 90% and some organisms contain particularly large amounts of water, such as jellyfish, the water accounts for 97% of their weight. The water content varies from organism to organism. Generally speaking, the water in aquatic organisms is more than that of terrestrial organisms. The water content in different organs of the same organism also varies. The active organs have more water and young animals also have more water than older animals.
There are two water states in living organisms: free water and bound water. Bound water and polar groups of organic compound are combined together to form hydrocolloids by hydrogen bond. They do not evaporate, flow and participate in metabolism. Free water is not tightly bound to organic compound and they can evaporate, flow and participate in metabolism. Polar water molecules are good solvents in which nutrients, wastes, hormones and other substances are dissolved and transported. Biochemical reactions also take place in water. When you squeeze a fruit, the flowing juice contains a lot of free water. It is also the main component of blood and tissue fluids.
The ratio of free water to bound water is not constant, they can be converted to each other. When the proportion of free water increases, the organism's metabolism is more active, but it is more sensitive to changes of environment. And when the bound water increases, the metabolic rate decreases, but its resistance to cold, drought and heat increases. For example, the plant will gradually increase its bound water to prevent frostbite for the coming winter. A sudden onset of cold wave can easily cause frostbite in plants because they do not yet have enough bound water or they are not ready for winter.