BIOL 150 Lecture 3 (p.1-35)

Importance of Water

• Over 70% of Earth's surface is covered by water, making it essential for life.
• All living organisms consist primarily of water, with most plants and animals containing over 60%.
• The human body is approximately 50-75% water by volume.

Uniqueness of Water

• Water is the only substance that naturally exists in all three physical states: solid (ice), liquid (water), and gas (steam).

Structure of Water

• Water is a polar molecule; it has an uneven distribution of charge due to oxygen’s higher electronegativity compared to hydrogen.
• Oxygen holds a slight negative charge (δ-), while hydrogen has a slight positive charge (δ+).

Chemical Polarity

• Polarity results from the separation of electric charge, leading to asymmetrical molecules and the presence of an electric dipole moment.
• Polar molecules contain polar bonds, which must possess a difference in electronegativity.

Hydrogen Bonding

• Polar nature allows water to form hydrogen bonds; each water molecule can create up to four H-bonds with neighboring molecules.
• Hydrogen bonds are crucial for many of water’s unique properties that support life.

States of Water

• Water can also exist as a supercritical fluid, a unique state where liquid and gas properties merge, typically found under extreme temperatures and pressures.

Density of Water

• The density of water is approximately 1 g/cm³.
• Water behaves uniquely as it contracts until reaching 4°C and then expands upon freezing, resulting in ice being about 9% less dense than liquid water. This is why ice floats.

Surface Tension

• Water has the highest surface tension among non-metallic liquids due to the cohesive forces between molecules at the surface.
• Surface tension allows small organisms, like water striders, to move across water surfaces.

Osmosis

• Osmosis is the movement of water through a semipermeable membrane from an area of low solute concentration to high solute concentration.
• It enables essential processes for maintaining homeostasis in plants and animals.

Cohesion and Adhesion

• Cohesion refers to water’s attraction to other water molecules due to hydrogen bonding.
• Adhesion is the attraction between water and other polar substances, such as spider silk.

Capillary Action

• Capillary action is driven by the adhesive properties of water, causing it to rise against gravity in thin spaces, such as the xylem of plants.
• Water's movement is also influenced by surface tension, which helps pull other water molecules along.

Temperature Regulation

• Water has a high specific heat capacity, meaning it absorbs significant heat before raising its temperature, crucial for temperature regulation in organisms.
• Water has an extremely high boiling point (100°C) due to hydrogen bonding, requiring substantial energy to convert from liquid to gas (heat of vaporization).

Climate and Ecosystem Impact

• Water regulates Earth's climate by absorbing solar heat, which is released during evaporation.
• This process stabilizes temperatures in aquatic ecosystems and helps prevent overheating in organisms.

Importance of Water

• Covers over 70% of Earth's surface and is vital for all life forms.
• Most plants and animals contain more than 60% water; humans are composed of 50-75% water.

Uniqueness of Water

• Exists in all three physical states: solid, liquid, and gas.
• Water is a polar molecule with an uneven distribution of charge, creating an electric dipole.

Chemical Polarity

• Polar molecules have distinct charges due to differences in electronegativity, leading to asymmetric geometries.
• Allows water molecules to form hydrogen bonds, with one water molecule capable of forming up to four hydrogen bonds.

States of Water

• A fourth state exists, known as a supercritical fluid, which occurs under extreme temperature and pressure, merging liquid and gas properties.
• In liquid water, hydrogen bonds are constantly breaking and reforming; cooling slows movement and eventually locks molecules in place as ice.

Density of Water

• Density is approximately 1 g/cm³.
• Water expands upon freezing, having a volume about 9% higher than in its liquid state, causing ice to float and impacting natural phenomena like frozen pipes.

Surface Tension

• Highest surface tension among non-metallic liquids due to the cohesion of water molecules at the surface.
• Allows insects like water striders to walk on water and influences water droplet formation.

Osmosis

• Movement of water from low solute concentration to high solute concentration through semipermeable membranes, crucial for maintaining homeostasis in living organisms.

Cohesion and Adhesion

• Cohesion refers to water's attraction to itself via hydrogen bonds; adhesion describes water's attraction to other polar substances.
• Capillary action leads to the ability of water to rise in narrow spaces, influenced by adhesion and cohesion forces.

Temperature Regulation

• High specific heat capacity means water can absorb considerable heat without significantly changing temperature, providing stability in biological systems.
• Water has a high boiling point and heat of vaporization, regulating the Earth's climate by absorbing and releasing solar energy during evaporation and condensation.

Implications in Biology

• Cohesion and adhesion facilitate water movement in xylem vessels in plants, essential for nutrient transport and stability in ecosystems.