biology vid 1

Polar molecule

A molecule where the overall charge is unevenly distributed, such as water.

Polar covalent bonds in water

Bonds where electrons spend more time near the oxygen atom than the hydrogen atoms, creating partial charges.

Hydrogen bonding in water

Weak bonds formed between water molecules due to their polarity attracting one another.

Four emergent properties of water

Cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent.

Cohesion

A phenomenon where hydrogen bonds hold water molecules tightly together.

Biological benefit of cohesion

Helps the transport of water and nutrients against gravity in plants.

Adhesion

The attraction between different substances, such as water molecules binding to plant cell walls.

Surface tension

A measure of how difficult it is to stretch or break the surface of a liquid.

Cause of water's high surface tension

Hydrogen bonding between molecules at the air-water interface and the water below.

Temperature moderation by water

Water absorbs heat from warmer air and releases stored heat to cooler air with minimal change in its own temperature.

Specific heat

The amount of heat that must be absorbed or lost for 1 gram of a substance to change its temperature by 1°C.

Specific heat of water

1 cal/g/°C (an unusually high value that helps water resist drastic temperature changes).

Hydrogen bonding relationship to specific heat

Heat is absorbed when hydrogen bonds break, and heat is released when hydrogen bonds form.

Calorie (cal)

The amount of heat required to raise the temperature of 1 gram of water by 1°C.

Kilocalorie (kcal)

Equal to 1,000 calories

Joule (J)

A unit of energy where 1 calorie equals 4.184 Joules.

Three states of matter

Water is the only common natural substance to exist in all three physical states (solid, liquid, gas) on Earth.

Evaporation

The transformation of a substance from a liquid state to a gaseous state.

Heat of vaporization

The quantity of heat that 1 gram of a liquid must absorb to be converted into gas.

Evaporative cooling

A process where the surface of a liquid cools down during evaporation as the hottest molecules escape.

Ecological role of evaporative cooling

Helps stabilize temperatures in living organisms (like sweating) and entire bodies of water.

Why ice floats on water

Hydrogen bonds in ice become more "ordered" and locked into a crystalline lattice, making solid ice less dense than liquid water.

Temperature of water's greatest density

4°C

Biological importance of floating ice

Insulates the water below

Environmental threat to icy habitats

Global warming from greenhouse gases (like carbon dioxide) is melting glaciers and Arctic sea ice, threatening animal survival.

Solution

A liquid that consists of a completely homogeneous mixture of two or more substances.

Solvent

The dissolving agent or component of a solution that is present in the largest amount.

Solute

The specific substance that is being dissolved in a solution.

Aqueous solution

A solution in which water acts as the dissolving agent (the solvent).

Why water is a versatile solvent

Its high molecular polarity allows it to attract and break apart many different types of charged substances.

Hydration shell

A sphere of water molecules that completely surrounds a dissolved ion to isolate it in a solution.

Substances water can dissolve besides ions

Nonionic polar molecules, as well as large molecules (like proteins) that possess ionic and polar regions on their surfaces.