Chapter 2 The Chemical Context of Life PowerPoint Lecture Presentations for Biology Eighth Edition p and Jane Reece Neil Campbell Lectures by Chris Romero updated by Erin Barley with contributions from Joan Sharp Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Overview A Chemical Connection to Biology Biology is a multidisciplinary science Living organisms are subject to basic laws of physics and chemistry One example is the use of formic acid by ants to maintain devil s gardens stands of Duroia trees Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Fig 2 1 Fig 2 2 EXPERIMENT Cedrela sapling li Duroia tree Inside unprotected Devil s garden Insect barrier Outside protected Inside protected Outside unprotected Dead leaf tiissue cm2 after on ne day RESULTS 16 12 8 4 0 IInside id I id Inside O t id Outside O t id Outside unprotected protected unprotected protected Cedrela saplings inside and outside devil s gardens Fig 2 2a EXPERIMENT Cedrela sapling Duroia tree Devil s garden Inside unprotected Insect barrier Inside protected p otected Outside protected Outside unprotected Fig 2 2b Dead d leaf tissu ue cm2 after one d a day RESULTS 16 12 8 4 0 Outside Inside Outside Inside unprotected protected unprotected protected Cedrela saplings inside and outside devil s gardens Concept 2 1 Matter consists of chemical elements in pure form and in combinations called compounds Organisms are composed of matter M Matter tt iis anything thi th thatt ttakes k up space and d has h mass Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Elements and Compounds Matter is made up of elements An element is a substance that cannot be broken down to other substances by chemical reactions A compound is a substance consisting of two or more elements in a fixed ratio A compound has characteristics different from those of its elements Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Fig 2 3 Sodium Chlorine Sodium chloride Fig 2 3a Sodium Fig 2 3b Chlorine Fig 2 3c Sodium chloride Essential Elements of Life About 25 of the 92 elements are essential to life Carbon hydrogen oxygen and nitrogen make up 96 of living matter Most of the remaining 4 consists of calcium phosphorus potassium and sulfur Trace elements are those required by an organism in minute quantities Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Table 2 1 Fig 2 4 a Nitrogen deficiency b Iodine deficiency Fig 2 4a a Nitrogen deficiency Fig 2 4b b Iodine deficiency Concept 2 2 An element s properties depend on the structure of its atoms Each element consists of unique atoms An atom is the smallest unit of matter that still retains the properties of an element Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Subatomic Particles Atoms are composed of subatomic particles Relevant subatomic particles include Neutrons no electrical charge Protons positive charge Electrons negative charge Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Neutrons and protons form the atomic nucleus Electrons form a cloud around the nucleus Neutron mass and proton mass are almost identical and are measured in daltons Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Fig 2 5 Cloud of negative charge 2 electrons Electrons Nucleus a b Atomic Number and Atomic Mass Atoms of the various elements differ in number of subatomic particles An element element s s atomic number is the number of protons in its nucleus An element s mass number is the sum of protons plus neutrons in the nucleus Atomic mass the atom s total mass can be approximated by the mass number Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Isotopes All atoms of an element have the same number of protons but may differ in number of neutrons Isotopes are two atoms of an element that differ in number of neutrons Radioactive isotopes decay spontaneously spontaneously giving off particles and energy Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Some applications of radioactive isotopes in biological research are Dating fossils Tracing atoms through metabolic processes Diagnosing medical disorders Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings TECHNIQUE Incubators Compounds including radioactive tracer 3 1 2 bright blue 10 C 15 C 20 C Human cells 1 Human cells are incubated with compounds used to make DNA One compound is labeled with 3H 2 The cells are placed in test tubes their DNA is isolated and unused labeled compounds are removed removed 4 25 C 5 30 C 6 35 C 7 40 C 8 45 C 9 50 C DNA old and new 3 The test tubes are placed in a scintillation counter RESULTS Counts s per minute 1 000 Fig 2 6 30 20 Optimum temperature for DNA synthesis 10 0 10 20 30 40 50 Temperature C Fig 2 6a TECHNIQUE Compounds including Incubators radioactive tracer 1 3 2 bright blue 20 C 10 C 15 C Human cells 1 Human cells are incubated with compounds used to make DNA One compound is labeled with 3H 2 The cells are placed in test tubes their DNA is isolated and unused labeled compounds are removed 4 25 C 5 30 C 6 35 C 7 40 C 8 45 C 9 50 C DNA old and new Fig 2 6b TECHNIQUE 3 The test tubes are placed in a scintillation counter Fig 2 6c Countts per minute C 1 000 RESULTS 30 20 Optimum t temperature t for DNA synthesis th i 10 0 10 20 30 40 50 T Temperature t C Fig 2 7 Cancerous throat tissue The Energy Levels of Electrons Energy is the capacity to cause change Potential energy is the energy that matter has because of its location or structure The electrons of an atom differ in their amounts of potential energy An electron s state of potential energy is called its energy level or electron shell Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Fig 2 8 a A ball bouncing down a flight of stairs provides an analogy for energy levels of electrons Third shell highest energy level Second shell higher energy level First shell lowest energy l level l b Atomic At i nucleus Energy absorbed Energy lost Electron Distribution and Chemical Properties The chemical behavior of an atom is determined by the distribution of electrons in electron shells The periodic table of the elements shows the electron distribution for each element Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Fig 2 9 Hydrogen 1H Atomic mass First shell 2 He 4 00 Atomic number Helium 2He Element symbol ElectronEl t distribution