Biology: Importance of Water in Sustaining Life

Study Notes

Water is essential for life on Earth
First cells likely originated in water and it remains the medium for most life processes
Water is:
A solvent for biochemical reactions
A transport medium
Involved in many chemical reactions (e.g., hydrolysis, photosynthesis)

Water molecules have a slightly positive charge (δ+) on hydrogen atoms and a slightly negative charge (δ-) on oxygen atoms due to unequal sharing of electrons
Hydrogen bonding occurs between water molecules due to their polarity
Hydrogen bonds are weak intermolecular forces that play a crucial role in water's physical and biological properties

Cohesion: attraction between water molecules (results in surface tension and allows for transport of water under tension in xylem)
Adhesion: attraction between water molecules and other polar molecules (results in capillary action in soil and plant cell walls)
Surface tension allows animals like water striders to walk on water and creates a habitat for them

Water is a polar solvent, allowing a wide variety of hydrophilic substances to dissolve
Most metabolic reactions occur in aqueous solutions, with reactants and enzymes dissolved in water
Some molecules (e.g., lipid hormones, wax cuticle) are hydrophobic and do not dissolve in water, but are essential for life

Buoyancy: water's density provides upward force, allowing aquatic animals to float or swim more easily
Viscosity: water's resistance to flow affects aquatic animals' movement and energy expenditure
Thermal conductivity: water's high thermal conductivity requires adaptations to reduce heat loss in aquatic animals
Specific heat capacity: water can absorb or release heat energy without significant temperature change, affecting aquatic animals' temperature regulation### Buoyancy in Ringed Seals
Ringed seals have a layer of blubber that allows them to remain buoyant in the sea, reducing the energy required to swim.
Buoyancy helps ringed seals conserve energy while swimming in the sea.

The streamlined body shape of ringed seals enables them to efficiently move through water.
Flippers use drag to facilitate movement in the water.

The layer of blubber insulates ringed seals when they are in water, reducing heat loss.
Ringed seals huddle together on land, reducing exposed surface area and minimizing heat loss.

Ringed seals are endotherms, maintaining a constant body temperature.
The high specific heat capacity of water helps ringed seals regulate their body temperature.

Black-throated loons can adjust their density by changing the volume of air in their air sacs, controlling their depth when swimming in water.
They can increase buoyancy in air by spreading their wings, increasing their surface area.
The hollow bones of birds further reduce their density, increasing buoyancy and allowing them to fly.

The streamlined shape of black-throated loons enables them to efficiently move through air and water.
Webbed feet help them move through water.

Black-throated loons maintain a constant body temperature as endotherms.
Feathers trap air, providing insulation, and are covered in a hydrophobic oil that keeps them dry.

The high specific heat capacity of water helps black-throated loons regulate their body temperature, especially when diving into cold water.

Hydrogen bonds, polar covalent bonds, and cohesion are intermolecular forces of attraction that affect biological systems.
Examples of biological processes that occur at or near surfaces include capillary action and metabolism.
Water's chemical bonding makes it a valuable coolant in living organisms due to its high specific heat capacity.