unit2 lecture2
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BIO 3
Introduction to Biology
Instructor: Francisca Herrera
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What is a living thing?
Living organisms are a carbon- and water-based cellular form with complex organization and heritable genetic information.
They undergo metabolism, possess a capacity to grow, respond to stimuli, reproduce, and, through natural selection, adapt to their environment in successive generations.
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Living organisms are:
water- and carbon- based
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Matter
Atoms
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Atoms
Organisms are chemical machines one must know chemistry in order to understand
biology Any substance in the universe that has mass
and occupies space is comprised of matter all matter is made up of atoms
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Atoms
All atoms have the same structure at the core is a dense nucleus
comprised of two subatomic particles
protons (positively charged)
neutrons (no associated charge)
orbiting the nucleus is a cloud of another type of subatomic particle
electrons (negatively charged)
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Atoms
An atom can be characterized by the number of protons it has or by its overall mass atomic number
the number of protons in the nucleus
mass number
the number of protons plus neutrons in the nucleus
electrons have negligible mass
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Atoms
Electrons determine the chemical behavior of atoms these subatomic components are the parts of the
atom that come close enough to each other in nature to interact
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Atoms
Electrons are associated with energy electrons have energy of position, called
potential energy the field of energy around an atom is arranged as
levels called electron shells within this volume of space, orbitals are where
electrons are most likely to be found
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Atoms
Electron shells have specific numbers of orbitals that may be filled with electrons atoms that have incomplete electron
orbitals tend to be more reactive atoms will lose, gain, or share electrons
in order to fill completely their outermost electron shell
these actions are the basis of chemical bonding
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Atoms
Ions – atoms that have gained or lost one or more electrons
Isotopes – atoms that have the same number of protons but different numbers of neutrons most elements in nature exist as mixtures of
different isotopes
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Atoms
Some isotopes are unstable and break up into particles with lower atomic numbers this process is known as radioactive decay
Radioactive isotopes have multiple uses nuclear medicine dating fossils
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Figure 3.5 Isotopes of the element carbon
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Simple Molecules
Water
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Molecules
Molecule forms when atoms are held together with energy
the energy (force) holding two atoms together is called a chemical bond
there are 3 principal types of chemical bonds1. ionic
2. covalent
3. hydrogen
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Molecules
Ionic bonds involve the attraction of opposite electrical charges
Molecules comprised of these bonds are often most stable as crystals
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Fig. 3.8
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Molecules
Covalent bonds form between two atoms when they share
electrons the number of electrons shared varies depending
on how many the atom needs to fill its outermost electron shell
covalent bonds are stronger than ionic bonds
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Figure 3.9 Water molecules contain two covalent bonds
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Molecules
Hydrogen bonds are weak bonds that form due to covalent bonds where one nucleus attracts the shared electrons more than another nucleus this attraction for electrons by a nucleus is called the
atom’s electronegativity
this results in partial charges in the atoms that are unequally sharing electrons
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Fig. 3.9
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Molecules
Hydrogen bonds form in association with polar molecules each atom with a partial charge acts like a magnet to bond
weakly to another polar atom with an opposite charge the additive effects of many hydrogen bonding interactions can
add collective strength to the bonds
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Figure 3.10 Hydrogen bonding water molecules
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Water
Water is essential for life the chemistry of life is water chemistry
Water is a polar molecule water can form hydrogen bonds hydrogen bonding confers on water many
different special properties
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Heat Storage water temperature changes slowly and holds
temperature well Ice Formation
few hydrogen bonds break at low temperatures water becomes less dense as it freezes because
hydrogen bonds stabilize and hold water molecules farther apart
High Heat of Vaporization at high temperatures, hydrogen bonds can be broken
(requires tremendous energy)
Water
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Fig. 3.11
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Water
Water molecules are sticky cohesion – when one water molecule is attracted to
another water molecule adhesion – when polar molecules other than water stick to
a water molecule
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Fig. 3.12
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Water
Water is highly polar in solution, water molecules tend to form the maximum
number of hydrogen bonds
hydrophilic molecules are attracted to water and dissolve easily in it
these molecules are also polar and can form hydrogen bonds
hydrophobic molecules are repelled by water and do not dissolve
these molecules are non-polar and do not form hydrogen bonds
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Fig. 3.13
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Water
The covalent bond within a water molecule breaks spontaneously
This produces two ions in a process called ionization because of the great strength of covalent bonds, this does
not occur too often
H2O OH- + H+
Water Hydroxide Hydrogen
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Water
The amount of ionized hydrogen from water in a solution can be measured as pH
The pH scale is logarithmic, which means that a pH scale difference of 1 unit actually represents a 10-fold change in hydrogen ion concentration
pH = -log[H+]
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Figure 3.14: The pH scale
ACIDIC:
more free H+
BASIC:
more free OH-
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Water
Pure water has a pH of 7 there are equal amounts of [H+] relative to [OH-]
The pH in most living cells and their environments is fairly close to 7 proteins involved in metabolism are sensitive to any pH
changes
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Water
Acids and bases are routinely encountered by living organisms from metabolic activities (i.e., chemical reactions)
from dietary intake and processing
Organisms use buffers to minimize pH disturbances
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Water
Buffer – a chemical substance that takes up or releases hydrogen ions
buffers don’t remove the acid or the base affecting pH but minimize their effect on it
most buffers are pairs of substances, one an acid and one a base
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Today’s Journal Entry
Under the activities menu of the virtual classroom, click on the Journals link
Topic 2 – Atoms and Simple Molecules
There are no wrong answers in the journal entries.
Answer in complete sentences, in a clear and concise manner.