Chapter 2 Quiz Biol

Covalent Bonds

- covalent bonds the sharing of electrons, join atoms into molecules - some atoms share electrons with other atoms, forming covalent bonds - atoms joined together by covalent bonds for molecules

atoms

- atoms consist of protons, neutrons, and electrons - the smallest particle of an element is an atom - different elements different atoms - an atom is made up of protons and neutrons located in the central nucleus - the nucleus is surrounded by electrons - protons are positive - electrons are negative

Covalent

- atoms in a covalently bonded molecule may share electrons equally, creating a non polar molecule - if electrons are shared unequally, a polar molecule is created

Chemical Elements (chnops)

- carbon - hydrogen - nitrogen - oxygen - phosphorus - sulfur

buffers

- cells that are kept close to pH 7 by buffers - buffers are substances that resist pH change - they accept H+ ions when they are in excess and donate H+ ions when they are depleted - function in homeostasis - buffers are not foolproof

atoms pt 2

- each atom is held together by attractions between the positively charged protons and negatively charged electrons - neutrons are electrically neutral - atoms of each element are distinguished by a specific number of protons - the number of neutrons may vary - variant forms of an element are called isotopes - some isotopes are radioactive - radioactive isotopes can be useful tracers for studying biological processes - PET scanners use radioactive isotopes to create anatomical images

in a polar covalent bond

- electrons are shared unequally between atoms, creating a polar molecule - water is a polar covalent molecule

compounds

- elements can combine to form compounds - chemical elements combine in fixed ratios to form compounds

hydrogen bonds

- hydrogen bonds are weak bonds important in the chemistry of life - the charged regions on water molecules are attracted to the oppositely charged regions nearby molecules

Ionic Bonds

- ionic bonds are attractions between ions of opposite charge - when atoms gain or lose electrons, charged atoms called ions are created - an electrical attractions between ions with opposite charges result in an ionic bond

ice is less dense than liquid water

- molecules in ice are farther apart than those in liquid water - ice is therefore less dense than liquid water, which causes it to float - if ice sank, it would seldom have a chance to thaw - ponds, lakes, and oceans would eventually freeze solid - ice hydrogen bonds are stable

like no other common substance, water exists in nature in all three physical states

- solid - liquid - gas - water makes up 75-85% of contents of most cells - hydrogen bonds make liquid water cohesive - due to hydrogen bonding, water molecules can move from a plants root to its leaves - insects can walk on water due surface tension created by cohesive water molecules - waters hydrogen bonds moderate temperature - it takes a lot of energy to disrupt hydrogen bonds - therefore water is able to absorb a great deal of heat energy without a large increase in temperature - as water cools, a slight drop in temperature releases a large amount of heat - this is the process of evaporative cooling

water is a versatile solvent

- solutes whose charges or polarity allow them to stick to water molecules dissolve in water - they form aqueous solutions - the chemistry of life is sesnitive to acidic and basic conditons - a compound that releases H+ ions in solutions is an acid, and one that accepts H+ ions in a solution is a base - acidity is measured on the pH scale - 0 to 6.99 is acidic - 7.01 to 14 is basic - pure water and solutions that are neither basic nor acidic are neutral with a pH of 7

basic atoms and molecules

- the emergence of a biological function starts at the chemical level - everything an organism is and does depends on chemistry - chemistry is in turn dependent on the arrangement of atoms in molecules - ultimately the atoms function by the rules of physics - life requires about 25 chemical elements - a chemical element is a substance that cannot be broken down to other substances by ordinary chemical means - 25 elements are essential to live