Transcript Atomic Structure

Water Chemistry and
Primary Productivity
Mrs. Daniels
IB HL/ AP
Biology
Revised September 2008
Atomic Structure
• Proton (p+):
A positively charged
particle found in the central core of an
atom (called the nucleus)
• Neutron (n0):
A neutral particle
found in the nucleus of an atom
• Electron (e-):
A tiny negatively
charged particle found outside of the
atomic nucleus
Atomic Structure
• The mass of a proton and a neutron is
relatively equal
• However, the electron has a mass equal to
1/1840 of a proton
• Which subatomic particles do you think
take up the most space in the atom?
Organization of the Atom
• The protons and neutrons are tightly
packed in a central core called the
nucleus
• If an atom were the size of a football
stadium, the nucleus would be a tiny
marble sitting in the center of it
• The electrons are found in different
layers (energy levels) of a “cloud”
around the nucleus
Atomic #
&
Mass #
• Elements differ because of the number
of protons they have
• The Atomic Number is the number of
protons
• The number of electrons in an atom
must equal the number of protons in
order for the atom to be neutral
• The Mass Number is the whole number
of protons plus neutrons in an atom
Atomic #
Mass
Number
&
Mass #
16
O
Atomic
Number
8
Chemical
Symbol
Mass # vs. Atomic Mass
Atomic
mass
20.18
Ne
Atomic
Number
10
Chemical
Symbol
Isotopes
• Isotopes of an atom occur when the number
of neutrons changes
• Isotopes have the same chemical properties
as the original atom because the charged
particles remain the same
• Later in the year, we’ll discuss radioactive
isotopes in more depth. Their role in biology
is very significant.
Atomic Mass
• A weighted average mass of the atoms
in a naturally occurring sample of an
element is called the Atomic Mass
• This number represents the mass as
well as the relative abundance of each
isotope
• Since atoms are so small, grams are not
typically used as units of mass
• Instead, an Atomic Mass Unit is used
(mathematically defined as 1/12th of the
mass of Carbon-12.)
Journal Entry #4 - part b
• Calculate this student’s grade if the class is
weighted as follows:
• Tests = 75%
Homework = 5%
• Lab = 10%
Final exam = 10%
Test scores: 89, 84, 72, 90
Lab :
99, 100, 98, 99, 94, 97
Homework : 92, 93, 96, 98, 105, 94
Final exam : 90
Journal Entry #4 – part b
• Calculate this student’s grade if the class is
weighted as follows:
• Tests = 75%
Homework = 5%
• Lab = 10%
Final exam = 10%
Test scores: 89, 84, 72, 90 = 335/4 = 83.75%
Lab : 99, 100, 98, 99, 94, 97 = 587/6= 97.8%
Homework : 92, 93, 96, 98, 105, 94 = 578/6= 96.3%
Final exam : 90%
83.75(.75) + 97.8(.10) + 96.3(.05) + 90(.10) =
86.4%
B
• Now if this teacher did NOT weight grades,
what would this student’s grade be?
Test scores:
Lab :
Homework :
Final exam :
89, 84, 72, 90
99, 100, 98, 99, 94, 97
92, 93, 96, 98, 105, 94
90
1590/1700 = 93.5%
A…very different
Valence Electrons
• The shell or energy level (n) containing
the outermost electrons for an element is
called the valence shell
• The electrons in that shell are called
valence electrons
• These electrons are the farthest from the
atom’s nucleus and are therefore the
easiest to remove
• Because of this, these are the electrons
involved in bonding.
Bonding
• Covalent bond – electrons are “shared”
– Polar – shared unequally
– Non-polar – shared equally
• Ionic – transfer of electrons causes change in
charge and electrostatic attraction between
ions
• Hydrogen – weak attraction between partially
positive and partially negative poles of H and
other atoms (N,O, F) polar covalently bonded
within different molecules
Other discussion-worthy topics
• Bonding – we’re going to continue with
bonding when we discuss water in a few
minutes
• Intermolecular forces – types and where you
would find examples of each
• Reactions – single, double, combustion, redox,
combination (synthesis), and decomposition
and where you would find examples of each in
biology
Water contributes to the fitness of
the environment
• One theory of the origin of life that it evolved in
•
•
•
•
water
Living cells are 70-95% H20
Water covers about 3/4 of the earth’s surface
It exist in three distinct phases in nature: solid,
liquid, and gas
The extraordinary properties of water are emergent
properties resulting from water’s structure and
molecular interactions
The polarity of water molecules results in
hydrogen bonding
• Water is a polar molecule; its polar
bonds and asymmetrical shape give
water molecule opposite charges on
opposite sides
• Each water molecule can form hydrogen
bonds to a max of four neighbors
+
+
+
+
-
+
- +
+
+
- +
+
Unique Properties of Water
– The uniqueness of water arises from the
emergent properties due to hydrogen bonding
that orders the molecule into a higher level of
organization
– Has cohesive behavior
– Resist change in temperature
– ~Has a high heat of vaporization and cools
surface as it evaporates
– Expands when it freezes
– Is a versatile solvent
– Ice floats (least dense as a solid)
Organisms depend upon the cohesion of water molecules
– Cohesion: Substance being held together by Hbonds
– Adhesion: water is attracted to and holds onto the
walls and overcomes gravity (this is the idea
behind capillary action)
– Capillary action- movement of water up vessels
against gravity, (xylem tubes)
– Surface Tension: measure of how difficult it is to
stretch or break the surface of a liquid
• hydrogen bonding is 20 X weaker than nonpolar
covalent bonds - so they form, break, and reform
constantly and dynamically giving water more structure
than most liquids
Water contributes to Earth’s habitability by
moderating temperatures
– Heat
• Kinetic energy
• Calorie (cal) 1 cal = 4.184 Joules (J)
• Joule (4.184 J = 1.00 cal
– Temperature
• Intensity of heat due to its average kinetic energy
• Celsius, Fahrenheit, Kelvin
• Convert from 0F to 0C by (9/5) 0C + 320
• Convert from 0C to 0F by (5/9) 0F - 320
• Convert from 0C and Kelvin by using 273
– Water’s high specific heat keeps temperature fluctuations
within a range suitable for life
• Water’s high Specific Heat: 1 cal/g/ o C
Evaporative cooling
• Vaporization (evaporation)- phase change from
•
•
•
liquid to a gas
Water has a relatively high heat of vaporization
(540 cal/g), which means that it requires a large
amount of energy for the liquid to break the
hydrogen bonds and leave the liquid state
The molecules left behind on the surface thus
have a lower kinetic energy and have a lower
temperature
Evaporative cooling stabilizes temperatures in
aquatic ecosystem, helps organisms from
overheating, and helps solar heat by tropical
seas dissipate
Oceans and lakes don’t freeze solid because ice
floats
– Water reaches its greatest density at 4 degrees
Celsius
– Water contracts as it cools to 40C, then as it cools
from 40C to freezing, it expands and becomes less
dense than liquid water…ice floats.
– Expansion of water:
• Prevents deep bodies of water from freezing solid
from the bottom up
• Ice forms on the top first because it is less dense.
As water freezes, it releases heat to the water
below it and insulates.
Hydrogen bonds create crystalline lattice
• As water cools, the molecules move slightly closer
to one another - as cooling continues, the
hydrogen bonds are not broken as often as in
warmer temps and as water reaches the freezing
point - a crystalline lattice forms as the molecules
“lock” into a hydrogen bonded position. This
bonding event organizes the molecules apart
slightly more than when they were still in the liquid
phase.
Water is the solvent of life
–
–
–
–
Solution- dissolved substances in liquids
Solute- the substance that dissolves
Solvent- liquid capable of dissolving
Aqueous solution
• Molarity- mol/liter of water
– Mole: amu or molecular mass (g) x Avogadro's #
– Molecular weight
– Hydrophilic- water loving (attraction to H2O)
– Hydrophobic- water hating (repels H2O)
– Concentration: Molarity
Organisms are sensitive to changes in pH
–
–
–
–
–
–
–
–
–
Hydrogen ion (H+)
Hydroxide ion (OH-)
Hydronium ion (H3O+) H+ bonded to H20
Acid (high concentration of H+) pH < 7
Base (high concentration of OH-) pH > 7
pH (scale ranging 0 to 14)
pH H+ 0H- = 1.0 x 10-14 M
pH = -log H+
Only 1 out of 554,000,000 molecules actually
dissociate
– Buffers- minimize pH change
Buffers
• Substances that prevent sudden changes in pH
• Help to minimize wide fluctuations in pH and
•
•
•
therefore help organisms maintain the pH of
body fluids within the narrow range necessary
for life
H2CO3 <---------> HCO3- + H+
In the presence of strong acid, it forms the
conjugate base and weak acid
In the presence of a strong base, it forms the
conjugate acid and a weak base
Acid precipitation threatens the fitness of
the environment
– Acid Precipitation (more acidic than 5.6 pH)
• Sulfur oxides & Nitrogen oxides react with water in
•
the air to form acids
Major source of oxides is combustion of fossil fuels
by industry and cars
– Lowers soil pH which affects mineral solubility
(throws things out of balance)
– Adverse affects on aquatic systems because of
lower pH of lakes and ponds
Aquatic Organisms
• We will be discussing several different
aquatic organisms this year
• Let’s turn our focus to protists
• Characteristics:
– Single-celled, aquatic, eukaryotic, some are
heterotrophic and some are autotrophic
• Photoautotrophs vs. chemoautotrophs
• Photoautotrophs vs. chemoheterotrophs
• Organisms that produce organic compounds
such as glucose, starch, and even
polyunsaturated fatty acids are called
PRODUCERS
• These are the autotrophs
• Ultimately LIGHT is the energy source for
most food chains
• What happens to the producers?
• They live, they produce, and they…
• Either get eaten by consumers or they die
and their nutrients are recycled.
Energy flow through ecosystems
Energy
from
sun
First
Second
Third
Fourth
trophic level: trophic level: trophic level: trophic level:
producers
primary
secondary
tertiary
consumers
consumers consumers
Producer
100%
(of harvested
energy…not 100%
of solar energy
hitting the surface of
the producer)
Primary
Consumer
~10%
Secondary
Consumer
~1%
Tertiary
Consumer
0.1%
Decomposers
(saprotrophs)
Quaternary
Consumer
0.01%
A food web at the edge of an eastern deciduous forest
-Simple food “chains”
are merely part of a
more complex food
web
-Is each organism
only assigned to ONE
trophic level?
Why or why not?
Pyramid of energy
Tertiary consumers (21)
Secondary consumers (383)
Saprotrophs (5,060)
Primary consumers (3,368)
Producers (20,810)
Notice that there is roughly a 90% reduction in energy
with each consecutive trophic level…WHY IS THIS TRUE?
-not all parts are used as a food source
-not everything is digestible
-heat loss
-some organisms never have the privilege of being eaten
Productivity
• Just like there is a difference between your
gross annual salary and your net, there is a
mandatory deduction that must be made to
the amount of energy trapped by producers
as organic matter
• Gross production - energy lost during
respiration = NET productivity
• SAPROTROPH – you’ve seen the word…what
does it mean?
• Organisms that live on or in non-living
organic matter (decomposers)
• Organisms that feed on non-living organic
matter, but don’t necessarily live on or in it
are called DETRITIVORES
• An organism can be a detritivore without
being a saprotroph, but all saprotrophs are
detritivores.
Accumulation of Biomass
• When producers convert light energy into
chemical energy stored in the bonds of
organic molecules, they increase in mass
• The mass of all (dried) organic matter is
referred to as BIOMASS
Pyramids of biomass
Secondary consumers (1)
Saprotrophs (10)
Primary consumers (4)
Producers
(40,000)
Tropical forest in Panama
Traditional pyramids of biomass tend to follow
traditional pyramids of energy