Water – The Medium of Life (Biological Science I)

Flashcards covering water’s properties, hydrogen bonding, emergent properties (cohesion, adhesion, surface tension), temperature regulation (specific heat, caloric units, heat of vaporization), evaporative cooling, freezing effects, and basic solution definitions.

What fraction of Earth's surface is covered by water?

Three-fourths (about 75%).

What percentage by weight of the living world is water?

60–70% by weight.

Water exists in which three states in the natural environment?

Ice, liquid water, and steam (gas).

Through what process is water redistributed on Earth?

Evaporation (the water cycle).

In a water molecule, how is oxygen bonded to hydrogen?

Oxygen covalently bonded to two hydrogen atoms.

What is the bond angle in a water molecule?

Approximately 105 degrees.

Which atom in H2O is more electronegative and attracts electrons more strongly?

Oxygen.

What causes water to be a polar molecule?

Unequal electron distribution due to oxygen’s electronegativity, giving O a slight negative charge and H a slight positive charge.

What type of interactions arise because of water’s polarity in the liquid state?

Hydrogen bonds (short-lived, constantly reforming).

How are water molecules arranged in the solid state (ice)?

Organized hydrogen bonds with four neighbors in 3D space; ice is less dense than liquid water and floats.

What are the three emergent properties of water important for life?

Cohesion, adhesion, and surface tension.

Define cohesion.

Attraction between water molecules due to hydrogen bonding.

Define adhesion.

Attraction between water and other substances (e.g., plant cell walls).

What is surface tension?

A measure of how hard it is to break the surface of a liquid; related to cohesion.

How does water moderate temperature?

By absorbing/releases a large amount of heat with only a small change in its own temperature due to high specific heat from hydrogen bonding.

What is the specific heat of water?

1 cal per gram per degree Celsius (1 cal/g/°C).

What is a calorie and what is a kilocalorie?

A calorie is the amount of heat required to raise 1 g of water by 1°C; 1 kilocalorie equals 1,000 calories.

What is the heat of vaporization?

The heat required to convert 1 g of liquid water to gas.

What is evaporative cooling?

Cooling of a surface as water evaporates and absorbs heat in the process.

Why is evaporative cooling important for living systems?

It helps stabilize temperatures in organisms and bodies of water.

At what temperature does water reach its greatest density?

4°C.

What happens to water when it freezes and why is this important for aquatic life?

Water expands upon freezing; ice is less dense than liquid water and floats, insulating bodies of water.

What is a solution?

A homogeneous mixture of a solvent and a solute.

What two components make up a solution according to the notes?

Solvent + solute.

What term is used to describe water’s ability to dissolve many substances?

Universal solvent.