Chapter 2 pt 1

Copyright © 2009 Pearson Education, Inc..

Including the lecture Materials of

Gregory AhearnUniversity of North Florida

with amendments andadditions by

John Crocker

Chapter 2pt 1

Atoms, Molecules, and Life

Copyright © 2009 Pearson Education Inc.

The main steps of the scientific method

Feedbackfalsifiable

Question

Research

Hypothesis

M & M/Data

Results:Experiment or

additionalobservation

Results does notsupport hypothesis; revise hypothesis or

pose new one

Results supports hypothesis; make

additional predictions and test them


If a hypothesis is correct, when we test it, we can expect a particular outcome

We try to disprove hypothesis. Control groups are tested along with

experimental groups to provide a comparison of results


Snowberry fly mimicking a jumping spider

Figure 1.3Cx


Case study: spider mimicry

Poun

ce ra

te (%

of t

rials

in

whi

ch s

pide

r jum

ped

on fl

y)

Control group(untreated flies)

Experimental group(wing markings masked)

Figure 1.3D


BiosphereEcosystem

-abiotic factors-all organisms

CommunityPopulationOrganism

ECOSYSTEM LEVELEucalyptus forest

COMMUNITY LEVELAll organisms ineucalyptus forest

POPULATION LEVELGroup of flying foxes

ORGANISM LEVELFlying fox

ORGAN SYSTEM LEVELNervous system

ORGAN LEVELBrain

Brain Spinal cord

Nerve

TISSUE LEVELNervous

tissue

CELLULAR LEVELNerve cell

MOLECULAR LEVELMolecule of DNA Figure 1.1


Organisms are made up of:organ systemsorganstissuescellsmolecules

ECOSYSTEM LEVELEucalyptus forest

COMMUNITY LEVELAll organisms ineucalyptus forest

POPULATION LEVELGroup of flying foxes

ORGANISM LEVELFlying fox

ORGAN SYSTEM LEVELNervous system

ORGAN LEVELBrain

Brain Spinal cord

Nerve

TISSUE LEVELNervous

tissue

CELLULAR LEVELNerve cell

MOLECULAR LEVELMolecule of DNA Figure 1.1


Each level of organization builds on the one below it

At each level, new properties emerge

ATOMS AND MOLECULES

Biological function starts at the chemical level


2.1 What Are Atoms?

Elements: substances that cannot be broken down by

ordinary chemical means (ex/ carbon) all atoms belong to one of 96 types of

naturally occurring elements life requires about 25 of these elements


2.1 What Are Atoms?

Atoms: basic structural unit of matter consist of charged particles

protons (+)neutrons (0)electrons (-)

smallest particle of an element each element has a unique number of protons

(atomic number)


Atoms of the same element with different numbers of neutrons are called isotopes of the element.

Some isotopes spontaneously break apart, forming different kinds of atoms and releasing energy in the process.

Such isotopes are radioactive. Example: radioactive uranium isotopes

decay and form lead in the process


Atoms are electrically neutral because they have and equal number of positive protons and negative electrons

Helium atom

2

2

2

Protons

Neutrons

Electrons

Nucleus


HYDROGEN (H)Atomic number = 1

CARBON (C)Atomic number = 6

NITROGEN (N)Atomic number = 7

OXYGEN (O)Atomic number = 8

Electron

Outermost electron shell (can hold 8 electrons)

First electron shell (can hold 2 electrons)

Electrons are arranged in shells Electrons orbit around atomic nuclei at specific

distances called electron shells the outermost shell determines the chemical

properties of an atom



Electrons can move from electron shell to electron shell. Electrons move

from an inner to an outer shell when absorbing energy.

Electrons move from an outer shell to an inner shell when releasing energy.

All life depends on this energy.

The energy boosts the electronto a higher-energy shell

The electron drops backinto lower-energy shell,releasing energy as light

energy

light

12

3

An electron absorbs energy

–

+ +

–

+

–


Energy Capture and Release

Life depends on electrons capturing and releasing energy Electron shells correspond to energy levels Energy exciting an atom causes an electron

jump from a lower- to higher-energy shell Later, the electron falls back into its original

shell, releasing the energy





2.2 How Do Atoms Form Molecules?

Molecules: two or more atoms of one or more elements held together by interactions among their outermost electron shells Atoms interact with one another according to

two basic principles:An inert atom will not react with other atoms

when its outermost electron shell is completely full or empty.

A reactive atom will react with other atoms when its outermost electron shell is only partially full.


Atoms Interact

Atoms will react with other atoms if the outermost shell is partially full (such atoms considered reactive) Example: Oxygen, with 6 electrons in

outermost shell (can hold 2 more electrons)


Atoms Interact

Reactive atoms gain stability by electron interactions (chemical reactions) Electrons can be lost to empty the outermost

shell Electrons can be gained to fill the outermost

shell Electrons can be shared with another atom

where both atoms have full outermost shells


Atoms Interact

Hydrogen and oxygen atoms gain stability by interacting with each other

Single electrons from each of two hydrogen molecules fill the outer shell of an oxygen atom



Atoms combine with each other to fill outer electron shells (e.g. hydrogen and oxygen have unfilled outer electron shells, and thus, can combine to form the water molecule).

The water molecule, with a filled outer electron shell, is more stable than either the hydrogen or oxygen atoms that gave riseto it.

The results of losing, gaining, or sharing electrons are chemical bonds—attractive forces that hold atoms together in molecules.



A molecule may be depicted in different ways.

Fig. 2-4

(a) All bonds shown

(b) Bonds within common groups omitted

(c) Carbons and their attached hydrogens omitted

(d) Overall shape depicted

CH3 CH2 CH2 CH2 OH

OH

CH

H

H

C

H

H

C

H

H

C O H

H

H



Types of bonds Ionic bonds: formed by passing an electron

from one atom to another One partner becomes positive, the other

negative, and they attract one another.Na+ + Cl– becomes NaCl (sodium chloride)Positively or negatively charged atoms are

called ions.+ cation - anion


Ions and Ionic Bonds Atoms that have lost electrons become

positively charged ions (e.g. sodium: Na+) Atoms that have gained electrons become

negatively charged ions (e.g. chlorine: Cl-) Oppositely charged ions are attracted to

each other are bound into a molecule by ionic bonds



Ions and Ionic Bonds

Salt crystals are repeated, orderly arranged sodium and chloride ions




Types of bonds (continued) Covalent bonds: bond between two atoms that

share electrons in their outer electron shell For example, an H atom can become stable

by sharing its electron with another H atom, forming H2 gas.


Covalent Bonds

Atoms with partially full outer electron shells can share electrons

Two electrons (one from each atom) are shared in a covalent bond


Covalent Bonds

Covalent bonds are found in H2 (single bond), O2 (double bond), N2 (triple bond) and H2O

Covalent bonds are stronger than ionic bonds but vary in their stability


Covalent Bonds

Most biological molecules contain covalent bonds


Covalent bonds produce either nonpolar or polar molecules. Nonpolar molecule: atoms in a molecule

equally share electrons that spend equal time around each atom, producing a nonpolar covalent bond



Nonpolar covalent bonding in hydrogen

(uncharged)

Electrons spendequal time neareach nucleus

Same charge onboth nuclei

(a)

++––

Nonpolar covalent bonding in hydrogen

Fig. 2-6a



Polar Covalent Bonds

Atoms within a molecule may have different nuclear charges

Those atoms with greater positive nuclear charge pull more strongly on electrons in a covalent bond



In diatomic molecules like H2, both atoms exert the same pulling force on bond electrons: the covalent bond is nonpolar




In molecules where atoms of different elements are involved (H2O), the electrons are not always equally shared: these covalent bonds are polar




A molecule with polar bonds may be polar overall

H2O is a polar molecule The (slightly) positively charged pole is

around each hydrogen The (slightly) negatively charged pole is

around the oxygen




Types of bonds (continued) Hydrogen bonds: weak electrical attraction

between positive and negative parts of polar molecules

Example: the negative charge of oxygen atoms in water molecules attract the positive charge of hydrogen atoms in other water molecules


Hydrogen Bonds

Polar molecules like water have partially charged atoms at their ends

Hydrogen bonds form when partial opposite charges in different molecules attract each other The partially positive hydrogens of one

water molecule are attracted to the partially negative oxygen on another


Hydrogen Bonds

Polar biological molecules can form hydrogen bonds with water, each other, or even within the same molecule

Hydrogen bonds are rather weak but can collectively be quite strong


Hydrogen bonds

Fig. 2-7

hydrogenbonds

O(–)

H(+)

H(+)

O(–)

H(+)

H(+)




Free Radicals

Some cellular reactions produce free radicals Free radical: a molecule whose atoms have

one or more unpaired electrons in their outer shells


Free Radicals

Free radicals are highly unstable and reactive Free radicals steal electrons, destroying

other molecules Cell death can occur from free radical attack


Free Radicals

Free radicals are involved in causing heart disease, Alzheimer’s, cancer, and aging

Antioxidants like vitamins C and E render free radicals harmless

Chapter 2 pt 1

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