water and life
Water and Life
Molecule That Supports All Life
Cells are composed of approximately 70–95% water.
Water’s versatility plays a crucial role in supporting life.
Statistics on Earth's water distribution:
97% of Earth's water is found in oceans.
2.4% is contained in glaciers and polar ice caps.
0.6% is found in rivers, lakes, and ponds (notably, 70% of freshwater is consumed by agriculture).
1.6% of water is located below ground in aquifers.
0.001% exists as vapor in the atmosphere.
A small amount of water is found in living organisms.
Water Molecules and Hydrogen Bonding
Water is classified as a polar molecule due to its structure.
Opposite ends of the water molecule hold opposite electrical charges.
Oxygen is covalently bonded to two hydrogen atoms, but due to unequal electron sharing, electrons spend more time closer to the oxygen atom.
Electronegativity: A measure of an element's ability to attract electrons when covalently bonded to another atom.
Hydrogen Bonding Between Water Molecules
Water molecules form hydrogen bonds, which significantly influence their properties.
Each water molecule can form up to 6 hydrogen bonds.
Four Properties of Water
Cohesion: Water molecules tend to stick together due to hydrogen bonding.
This property allows for the transport of water against gravity in vascular plants.
Adhesion: Water can form hydrogen bonds with other substances, aiding in its movement in various environments.
Capillary Action: Occurs in small tubes; it results from adhesion being stronger than cohesion.
The liquid is pulled upward along the sides of the tube, working against gravity.
Surface Tension:
Defined as the cohesion of water molecules at the water-air interface.
Molecules at the surface form stronger bonds, demonstrated by certain organisms (e.g., basilisk lizards) that can walk on water due to surface tension.
Heat and Water's Temperature Resistance
Water possesses a high specific heat capacity, which is the amount of heat energy needed to change the temperature of 1 gram of water by 1ºC. This capacity helps moderate temperature changes in the environment.
Due to hydrogen bonds between molecules, a significant amount of heat must be absorbed before the temperature of water increases.
Compared to other materials (e.g., Aluminum: 0.215 cal/gm K; Water: 1.00 cal/gm K), water requires more energy to raise its temperature.
Heat and its Definition
Heat: Energy that is transferred due to a temperature difference. It is essentially kinetic energy arising from the motion of molecules.
Heat flows from areas of higher energy (hotter) to lower energy (cooler) through processes such as conduction.
Evaporative Cooling
Evaporative cooling occurs as water evaporates, cooling the surface it leaves behind.
Specifically, the most energetic (warm) molecules escape as steam, leaving cooler ones behind.
Example: Sweating as a means to cool the body.
Temperature Measurements
Temperature measures the intensity of heat and is usually expressed in degrees Celsius (°C).
Notable temperature points include:
Ice = 0°C
Room Temperature = approximately 20-22°C
Body Temperature = approximately 37°C
Boiling Point of Water = 100°C
Global Warming and Ocean Temperature
Global warming results in ocean warming, with the distribution of heat primarily going into:
93% into oceans
3% into melting ice
3% into continents
1% into the atmosphere.
The heating rates have changed dramatically:
The upper ocean layer (0-700 m) has warmed at four times the rate it did between 1960-1991 during the 1992-2015 timeframe.
The deeper ocean layer (700-2000 m) is now warming at nine times the rate observed in previous decades.
Overall, ocean temperatures have risen approximately 0.13°C per decade over the last century.
Ice Density and its Implications
Ice floats on water, indicating that it is less dense than liquid water. This phenomenon prevents bodies of water from freezing solid, preserving aquatic life.
Water is most dense at 4°C; as it cools further to form ice, hydrogen bonds arrange molecules further apart, thus creating less density in ice relative to liquid water.
Water as a Solvent
Water is known as a great solvent due to its ability to dissolve many nutrients and wastes.
The mixture comprised of substances in water is known as a solution:
Solvent: The dissolving agent (in this case, water).
Solute: The substance that gets dissolved.
Hydrophilic substances have an affinity for water, while hydrophobic substances do not interact with water.
pH and Solutions
Changes in concentrations of hydrogen ions
Hydrogen ions [H+] and hydroxide ions [OH–] can dramatically affect cellular processes.
Pure water has a concentration of hydronium ions [H+] = [OH–] = 1 x 10^-7 moles per liter (indicating a neutral pH of 7).
pH: Defined as pH = -log[H+]. The logarithmic nature of the pH scale indicates that each whole number change on the scale reflects a tenfold change in hydrogen ion concentration.
The pH scale runs from 0 to 14:
Acidity is indicated by pH < 7 (higher hydrogen ion concentration).
Basic solutions are indicated by pH > 7 (lower hydrogen ion concentration).
A neutral solution is represented by a pH of 7.
Buffer Systems and Their Relevance
Buffers are substances that resist changes in pH. Examples include Alka-Seltzer and TUMS.
A critical buffer system in the human blood maintains a pH between 7.35 and 7.45, which is essential for proper biological function:
Reaction: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- (Carbonic acid-Bicarbonate ion equilibrium).
Acidosis occurs if blood pH drops dangerously low (below 7.4), impacting various body systems and can be a result of respiratory issues, kidney failure, or other imbalances.
The body will compensate for acidosis by increasing respiration rates to expel CO2 and by expelling more hydrogen ions in urine.