BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 2 The Chemical Basis of Life Modules 2.1 – 2.8

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

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

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

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

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

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Carbon, hydrogen, oxygen, and nitrogen make up the bulk of living matter, but there are other elements necessary for life Table 2.2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Goiters are caused by iodine deficiency Figure 2.2

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chemical elements combine in fixed ratios to form compounds Example: sodium + chlorine  sodium chloride 2.3 Elements can combine to form compounds

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An atom is made up of protons and neutrons located in a central nucleus Figure 2.4A A. Helium atom Protons Neutrons Electrons Nucleus The nucleus is surrounded by electrons

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each atom is held together by attractions between the positively charged protons and negatively charged electrons Figure 2.4B B. Carbon atom Protons Neutrons Electrons Nucleus Neutrons are electrically neutral

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

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Electrons are arranged in shells –The outermost shell (valence 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

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 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 Na Sodium atom Cl Chlorine atom Na + Sodium ion Cl – Chloride ion Sodium chloride (NaCl) NaClNaCl + –

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sodium and chloride ions bond to form sodium chloride, common table salt Figure 2.7B Na + Cl – Figure 2.7Bx

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

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Molecules can be represented in many ways Table 2.8

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hydrogen Bonds –Water is a compound in which the electrons in its covalent bonds are shared unequally. This causes it to be a polar molecule, one with opposite charges on opposite ends.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The polarity of water results in weak electrical attractions between neighboring water molecules. –Hydrogen bond– formed between a hydrogen that is attached to a highly electronegative atom (O, N) and another highly electronegative atom of separate molecule

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Acknowledgements Unless otherwise noted, illustrations are credited to Pearson Education have been borrowed from BIOLOGY: CONCEPTS AND CONNECTIONS 4th Edition, by Campbell, Reece, Mitchell, and Taylor, ©2003. These images have been produced from the originals by permission of the publisher. These illustrations may not be reproduced in any format for any purpose without express written permission from the publisher.