BIO SCI 93 Study Guide - Midterm Guide: Covalent Bond, Atomic Mass (Band), Thyroid

Biological Sciences
Course Code
Jorge Busciglio Kim Green Marcelo A Wood
Study Guide

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Introduction: Themes in the Study of Life
-Biology- the study of Life
-Levels of Biological Organization
● The biosphere (Earth) Ecosystem (Ontario) Communities (entire array of organism
inhibiting an entire ecosystem) populations (specific individuals of a species)
organisms (individual living things) organs and organ systems tissues cells
organelles molecules
-Some Properties of Life:
1. Order
2. Evolutionary Adaption
3. Response to the Environment
4. Reproduction
5. Growth and Development
6. Energy Processing
7. Regulations
The Chemical Context of Life
*Matter consists of Chemical Elements in Pure Form and in Combinations called Compounds
-Organisms are composed of Matter-anything that takes up space and has mass
A. Elements and Compounds
-Element-a substance that cannot be broken down to other substances by
chemical reactions
-Compound-a substance consisting of 2 or more different elements combined
in a fixed ratio (ex: NaCl is composed of Na and Cl in a 1:1 ratio)
B.  The Elements of Life
-20-25% of the elements are essential elements that an organism are required to have in
order to live a healthy life/reproduce
-Carbon, Oxygen, Nitrogen, and Hydrogen make up 96% of living matter (CONH)
-Trace Elements-are required by organisms in only minute quantities (Fe, I, Zn, Cu)
Iron (Fe) is needed in all forms of life-- Red Blood Cells
● Iodide (I) is essential for vertebrates (animals with backbones), produced by the
thyroid gland, deficiency of Iodide can cause goiter (when the thyroid gland to
grow to a abnormal size)
* An element’s properties depend on the structure of its atoms
-Atom-the smallest unit of matter that still retains the properties of an element
A. Subatomic Particles
-Proton, Neutron, Electron
-Atomic Nucleus- the region where the protons and neutrons are packed together tightly in a
dense core
-Neutron and Proton have almost identical mass ~1.7x10^-24 g
● Can be measured in dalton=atomic mass unit (amu)
B. Atomic Number and Atomic Mass
-Atomic Number- the number of protons
-Mass Number- sum of the protons and neutrons of an atom
-Atomic Mass-the average mass of all the natural occurring isotopes of an element
C. Isotopes-the different atomic forms of the same element (different # neutrons)

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-Radioactive Isotopes-the nucleus is unstable, decays spontaneously=giving off particle/energy
● Decay can lead to change in # of protons= change in element
● Measurement of radioactivity in rocks = dating fossils
● Metabolic tracers that follow atoms through metabolism (ex: certain kidney
diseases/disorders could be diagnosed by injecting small amts of radioactive isotopes into
the blood and measuring the amt of tracers excreted in the urine)
D. The Energy Levels of Electrons
-Energy-capacity to cause change by doing work
-Potential Energy-the energy that matter possesses b/c of its location/structure (energy of a
static/stationary item)
● Electron’s energy is correlated w/ its average distance from the nucleus
-Electron Shells- characteristic average distance and energy level
● Closes to nucleus=lowest potential energy
● Electrons can change shell it occupies by absorbing/losing amt of energy= the difference in the PE
from old shell and new shell
● Light excites electron to new energy shell=farther away from nucleus (Ex: sunlight excites
electrons in the surface of a car, when electrons fall back to original levels they release energy
which is why the surface of a car is hot when exposed to sunlight for a long period of time)
E. Electron Distribution and Chemical Properties
-chemical behaviors = distribution of electrons in shell and the # of electrons in the outermost
shell (valence electrons)
F. Electron Orbitals
-Orbitals-3D space that electrons are found 90% of the time
● 1st shell- only spherical s orbital (1s)
● 2nd shell-4 orbital- 1 large s orbital (2s) and 3 dumbbell shaped p orbitals (2p)
● 2 electrons per orbital
*The formation and function of molecules depend on chemical bonding between atoms
-Chemical Bonds-atomic interactions that results in atoms staying close together (Intramolecular)
A. Covalent Bonds-sharing of a pair of valence electrons by 2 atoms
-Molecule-2 or more atoms held together by covalent bond
● Can be expressed in 3 ways- molecular formula, lewis dot structure, structural formula
-Compound-2 or more elements combined in a fixed ratio
-Electronegativity- the attraction of a particular atom for the electrons of a covalent bind
● The more electronegative an atom is the more strongly it pulls shared electrons toward itself
Nonpolar covalent bond- when the atoms have the same electronegativity (the electrons are
shared equally)
Polar covalent bond-unequal sharing of electrons→ results in partial charges within the molecule
(Ex: water)
B. Ionic Bonds-transfer of electrons
-results in ions (a charged atom)
Cation-positively charged ion
Anion-negatively charged ion
● b/c of their opposite charges- they are attracted to one another
-Ionic Compound-compounds formed by ionic bonds (Ex: NaCl, salt )
C. Weak Chemical bonds (Intermolecular forces)
-within/between the molecules
Van der waals Interactions-nonpolar molecules have positive/negative charged regions

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Hydrogen Bonds- noncovalent attractions b/t a hydrogen and an electronegative atom,
attraction b/t the lone pair of an electronegative atom and a hydrogen atom that is bonded
to either nitrogen, oxygen or fluorine
Dipole-Dipole Interactions-electrostatic interactions b/t permanent dipoles in molecules,
align the molecules to increase attraction (Ex: HCl- the positive end of a polar molecule
will attract the negative end of the other molecule and influence its position )
D. Molecular Shape and Function
-shapes are determined by positions of the atom’s orbitals
-shapes are crucial b/c determines how biological molecules recognize/respond to one another
*Chemical Reactions make and break chemical bonds
-Chemical Reactions-making and breaking of chemical bonds, leading to a composition
-Reactants + Reactants  Products
● Ex: Photosynthesis, Cellular respiration
● All chemical Reactions are reversible
-Factors that affect chemical reactions
● Concentration of Products and Reactants
● The presence of enzymes/catalyst
-Chemical Equilibrium-the point at which the reactants offset one another exactly
● forward/reverse reactions are still going but no net effect on the concentration
● Dynamic equilibrium-reactions are still going but no net effect on concentration of reactants and
products, concentrations have stabilized at a particular ratio
Water and Life
*Polar covalent bonds in water molecules result in hydrogen bonding
-unequal sharing of electrons, partial charge, makes water possess a V shape
-water can make 4 hydrogen bonds
*Four emergent properties of water contribute to Earth’s suitability for life
-cohesion/adhesion, ability to moderate temperature, expansion upon freezing, versatility as a
A. Cohesion of water molecule
-Cohesion-hydrogen bonds between water molecules helps hold together the column of water
within the cells
-Adhesion-hydrogen bonds between water molecules and other molecules
-Surface tension-measure of how difficult it is to stretch or break the surface of liquid
● Water has a greater surface tension than other liquids
B. Moderation of Temperature of Water
-absorbs large amt of heat w/ only a slight change in its own temperature (high specific heat)
-Specific Heat-amt of heat that must be absorbed or lost for 1g of that substance to change its
temperature by 1 C
-Evaporative Cooling-hottest molecules leave as vapor/gas
-Heat of vaporization- the quality of heat a liquid must absorb for 1g of it to be converted from
liquid to the gaseous state
C. Floating of Ice on Liquid Water
-less dense solid than liquid thus ice floats on water- due to hydrogen bonds
D. Water the solvent of Life
-Solutions-liquid that is completely homogenous mixtures of 2 or more substances
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