AP Biology- Polarity, Water Molecules, & Elements of Life

polarity

unequal sharing of the electrons makes water a polar molecule

hydrogen bond

Attraction between a slightly positive hydrogen atom and a slightly negative atom.

Crystalline structure of ice

Water becomes less dense as it freezes, causing a crystal-like structure to form.

Adhesion

An attraction between molecules of different substances

Cohesion

Attraction between molecules of the same substance

capillary action

the upward movement of water due to the forces of cohesion, adhesion, and surface tension

Temperature Control

Water has a high specific heat, meaning it will resist change in temperature.

Density

as water solidifies, it expands and becomes less dense

Explain why water can go through the xylem of a leaf.

Due to the forces of adhesion, this allows for water to cling to the cell walls, resisting the downward pull of gravity. As water travels up the cell walls, cohesion ensures that the water molecules stick together.

Explain how water molecules connect to each other.

Hydrogen bonds! The partial positive hydrogens bond to the partially negative oxygens, bonding the molecules together.

How are water molecules formed?

by covalent bonds that link two hydrogen atoms to one oxygen atom

Universal Solvent

its polar molecules are attracted to ions and other polar molecules it can form hydrogen bonds with other substances.

Matter

Anything that has mass and takes up space

Elements

any substance that cannot be broken down into simpler substances

Compound

a thing that is composed of two or more separate elements; a mixture.

dehydration reaction

A chemical reaction in which molecules combine by removing water

hydrolysis reaction

A chemical reaction that breaks apart a larger molecule by adding a molecule of water

electronegativity trend

increases up and to the right

Essential Elements of Life

carbon, hydrogen, oxygen, nitrogen, phosphorus

Importance of high specific heat

moderates air temperature

stabilizes ocean temperature

organisms can resist changes in their own internal temperature

Importance of evaporative cooling

- moderates Earth's climate

- stabilizes temp in lakes and ponds

- prevents terrestrial organisms from overheating

- prevents leaves from becoming too warm in the sun

Octet Rule

States that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons

What do variations in the carbon skeleton allow for?

molecular diversity

When does capillary action occur?

When adhesion forces outweigh cohesion forces