Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Rattlebox moths release a chemical that spiders don’t like This spider caught

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Rattlebox moths release a chemical that spiders don’t like

• This spider caught a rattlebox moth and then let it go


• Thomas Eisner pioneered chemical ecology

– the study of the chemical language of nature

• He studies how insects communicate via chemical messages

Thomas Eisner and the Chemical Language of Nature


• Everything an organism is and does depends on chemistry

• Chemistry is in turn dependent on the arrangement of atoms in molecules

• In order to understand the whole, biologists study the parts (reductionism)

2.1 The emergence of biological function starts at the chemical level

ATOMS AND MOLECULES


• Molecules and ecosystems are at opposite ends of the biological hierarchy

– Each level of organization in the biological hierarchy builds on the one below it

– At each level, new properties emerge


• A biological hierarchy

Figure 2.1 A. Molecule: Actin Atom

MyosinActin

B. Organelle: Myofibril (found only in muscle cells)

Myofibril (organelle)

C. Cell and tissue: Muscle cell within muscle tissue

Rattlebox moth

D. Organ: Flight muscle of a moth


• A chemical element is a substance that cannot be broken down to other substances by ordinary chemical means

• About 25 different chemical elements are essential to life

2.2 Life requires about 25 chemical elements


• Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life

Table 2.2


• Goiters are caused by iodine deficiency

Figure 2.2


• Chemical elements combine in fixed ratios to form compounds

• Example: sodium + chlorine sodium chloride

2.3 Elements can combine to form compounds


• The smallest particle of an element is an atom

• Different elements have different types of atoms

2.4 Atoms consist of protons, neutrons, and electrons


• An atom is made up of protons and neutrons located in a central nucleus

Figure 2.4A A. Helium atom

2

2

2

Protons

Neutrons

Electrons

Nucleus

• The nucleus is surrounded by electrons


• Each atom is held together by attractions between the positively charged protons and negatively charged electrons

Figure 2.4B B. Carbon atom

6

6

6

Protons

Neutrons

Electrons

Nucleus

• Neutrons are electrically neutral


• Atoms of each element are distinguished by a specific number of protons

Table 2.4

– The number of neutrons may vary

– Variant forms of an element are called isotopes

– Some isotopes are radioactive


• Radioactive isotopes can be useful tracers for studying biological processes

• PET scanners use radioactive isotopes to create anatomical images

2.5 Connection: Radioactive isotopes can help or harm us

Figure 2.5BFigure 2.5A


• Electrons are arranged in shells

– The outermost shell determines the chemical properties of an atom

– In most atoms, a full outer shell holds eight electrons

2.6 Electron arrangement determines the chemical properties of an atom


• Atoms whose shells are not full tend to interact with other atoms and gain, lose, or share electrons

Figure 2.6

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)


• When atoms gain or lose electrons, charged atoms called ions are created

– An electrical attraction between ions with opposite charges results in an ionic bond

2.7 Ionic bonds are attractions between ions of opposite charge

Figure 2.7A

NaSodium atom

ClChlorine atom

Na+

Sodium ionCl–

Chloride ion

Sodium chloride (NaCl)

Na Cl Na Cl

+–


• Sodium and chloride ions bond to form sodium chloride, common table salt

Figure 2.7B

Na+

Cl–


• Some atoms share outer shell electrons with other atoms, forming covalent bonds

– Atoms joined together by covalent bonds form molecules

2.8 Covalent bonds, the sharing of electrons, join atoms into molecules


• Molecules can be represented in many ways

Table 2.8

Documents

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Rattlebox moths release a chemical that spiders don’t like This spider caught