Life and its Foundations
What is life? What does it mean to be
living?
 Living depends on fundamental principles
of Physics.
 Living depends on fundamental principles
of Chemistry.

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Life is like pornography
(you’ll recognize it if you see it)

“Life” is difficult to define
 There
are several attributes that living things
have that set them apart from non-living
things.
 Not every biologist has exactly the same list,
but something similar.
 Some non-living things have one or more of
these characteristics, but that’s all.
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Living things have a complex, often
hierarchical structure



Consider your liver. It consists of
 Hepatocytes that do the job of the liver.
 Blood vessels: supply cells w/ nutrients, O2
 Connective tissue: holds the organ together
 Immune system cells: protect against germs
Tissues are made of individual cells
Cells are made of organelles
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All living things are made of cells

Robert Hooke, 1600’s
 Looked
at cork (part of wood from a tree) with
a microscope and saw little compartments.

Schleiden, Schwann, and Virchow:
Cell Theory
 All
living things are made of cells
 All cells arise from pre-existing cells.
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Living things perform chemical
reactions

Microbes make acids or alcohols
 Beer,

wine, bread are made by living things.
Your brain, right now
 Burning
sugar to power the taking in and
processing of information.
 Nerve cells producing chemical signals,
releasing them, then breaking them down.
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Living things obtain energy from
their surroundings

Plants perform photosynthesis
 Use

sunlight energy
Humans ingest plants, animals, even fungi
 We
use pre-existing organic matter as our
nutrient source for energy

Microbes have wide array of energy
sources
 Organic
material, sunlight, even minerals
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Living things respond to their
environment

Plants
 Bend
toward sun; grow up, opposite pull of
gravity; respond to touch.

Humans respond to temperature. Cold?
 Physiological
response: hairs stand up, chills.
 Behavioral response: go put on a sweater.

Bacteria: chemotaxis, sense nutrient and
swim towards it.
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Living individuals change over time

Plants, animals grow, mature.
 Organisms
reach reproductive age, produce
seeds, go through puberty, etc.
Even bacteria double in size before
dividing into two cells.
 Many organisms are programmed to
change in a certain way over their life span

 E.g.
egg, tadpole, frog
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Living things reproduce

All produce young of the same type
 E.
coli cells divide and become more E. coli
cells.
 If they didn’t reproduce, then they wouldn’t be
here, would they!
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Living things share a common
evolutionary history

Cells, the basic unit of life, are highly
similar to one another.
 Genetic
information is coded for in DNA
 Proteins are the major tools of a cell
 The inside of a cell is separated from the rest
of the world by a cell membrane made of
phospholipids and proteins.
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Living things maintain a constant
internal environment: Homeostasis

Humans
 Your
blood maintains a pH of about 7.4
 Your body stays about 37°C
 Much, much more

Even unicellular organisms, including
bacteria, attempt to keep their insides from
changing too much.
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There’s no doubt a squirrel is alive.
What about a virus?

Viruses are particles
 made
of at least two kinds of molecules,
proteins and nucleic acids (like DNA)
 No cell membrane or other structures
associated with cells.
 Violate Cell Theory (all living things made of
cells). But what if Not ALL living things ARE
made of cells. Then what?
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Life and Physics

First Law of Thermodynamics
 Matter
cannot be created or destroyed
 Matter and energy are interchangeable

Second Law of Thermodynamics
 All

things tend towards entropy (randomness)
At various points we will see the effects of
these on the function of living things.
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Life and Chemistry
Matter is anything that occupies space
and has mass.
 Elements are substances which cannot
be split into simpler substances by
ordinary chemical reactions.
 Each element has a one or two letter
chemical symbol.

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The Essential Elements of Life
Living things are made of the same
elements as everything else is.
 The big 6: CHONPS

 Carbon,
hydrogen, oxygen, nitrogen,
phosphorous, and Sulfur

The next 6: salts and metals
 Calcium,
Potassium, sodium, chlorine,
Magnesium, and iron. (Ca, K, Na, Cl, Mg, Fe)

Trace elements: needed in tiny amounts
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Matter is made up of Atoms
Atoms are the smallest unit of an element that
still has the chemical properties of that element.
Atoms:
Have a central nucleus
Protons (+)
Neutrons (0)
Orbitals on the outside that hold
Electrons (-)
The number of protons determines what the
element is
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Atomic number = the number of protons in the
atom.
Atomic weight (or Mass number) = the total
number of protons and neutrons.
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Isotopes are atoms of an element that all
have the same number of protons, but have
different numbers of neutrons.
All are Carbon, but are isotopes. The first 2
are “stable”, but the third is a radioisotope, a
radioactive element that “decays” into
another kind of element and gives off
radiation.
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When two or more atoms combine in a
chemical reaction, a molecule is formed. This
molecule may have very different properties
than the elements that formed it.
When a molecule contains two or more atoms
of different elements, it is called a compound.
CO2
H 2O
NaCl
C12H22O11
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Atoms are held together by forces of attraction
called chemical bonds.
Ionic bonds
Covalent bonds
Hydrogen bonds
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In an ionic bond electrons are transferred
from one atom to another. Opposing charges
hold the atoms together.
An ion is a charged particle (atom or molecule).
Na+
Cl-
Ca++
positive charge - cations
HCO3- negative charge – anions
Ionic bonds easily come apart when such
molecules are dissolved in water, so they aren’t
very important in cells which are mostly water.
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Covalent bonds are formed when atoms
share electrons. These are the strongest
bonds.
C-C
Double covalent bonds
C=C
Triple covalent bonds
N≡N
(atmospheric nitrogen)
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