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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 defineThere 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’sLooked at cork (part of wood from a tree) with

a microscope and saw little compartments. Schleiden, Schwann, and Virchow:

Cell TheoryAll living things are made of cellsAll 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 sourcesOrganic 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 spanE.g. egg, tadpole, frog

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Living things reproduce

All produce young of the same typeE. 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 DNAProteins are the major tools of a cellThe 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 7.4Your 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 ThermodynamicsMatter cannot be created or destroyedMatter and energy are interchangeable

Second Law of ThermodynamicsAll 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 metalsCalcium, 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 holdElectrons (-)

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 H2O 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+ Ca++ positive charge - cations Cl- 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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