General Biology 1004 Chapter 2 Lecture Handout, Summer 2005 Dr. Frisby

Transcription

1 Slide 1 BIOLOGY AND SOCIETY: FLUORIDE IN THE WATER There has been a sharp decline in tooth decay in the last few decades The use of fluoride in drinking water illustrates the point that organisms are chemical systems Slide 2 TRACING LIFE DOWN TO THE CHEMICAL LEVEL Biology includes the study of life at many levels In order to understand life, we will start at the macroscopic level, the ecosystem, and work our way down to the microscopic level of cells Cells consist of enormous numbers of chemicals that give the cell the properties we recognize as life Slide 3 Ecosystem African savanna Community All organisms in savanna Organism Zebra Population Herd of zebras Organ system Circulatory system Organ Heart Cell Heart muscle cell Tissue Heart muscle tissue Molecule DNA Atom Oxygen atom Figure 2.1

2 Slide 4 SOME BASIC CHEMISTRY Take any biological system apart and you eventually end up at the chemical level Slide 5 Matter: Elements and Compounds Matter is anything that occupies space and has mass Matter is found on the Earth in three physical states Slide 6 Matter is composed of chemical elements Elements There are 92 naturally occurring elements on Earth

3 Slide 7 All the elements are listed in the periodic table Atomic number Element symbol Mass number Figure 2.2 Slide 8 Twenty-five elements are essential to life Figure 2.3 Slide 9 Trace elements are essential for life An iodine deficiency causes goiter Figure 2.4

4 Slide 10 Elements can combine to form compounds Slide 11 Atoms Each element consists of one kind of atom Nucleus (a) (b) Cloud of negative charge (2 electrons) 2 Protons 2 Neutrons 2 Electrons Figure 2.5 Slide 12 The Structure of Atoms Atoms are composed of subatomic particles 2 Protons 2 Neutrons 2 Electrons

5 Slide 13 Most atoms have protons and neutrons packed tightly into the nucleus 2 Protons 2 Neutrons 2 Electrons Slide 14 Elements differ in the number of subatomic particles in their atoms The number of protons, the atomic number, determines which element it is An atom s mass number is the sum of the number of protons and neutrons Mass is a measure of the amount of matter in an object Slide 15 Isotopes Isotopes are alternate mass forms of an element Table 2.1

6 Slide 16 Radioactive isotopes Radioactive isotopes have many uses in research and medicine Slide 17 Example: PET scans Hearing words Seeing words (a) (b) Speaking words Generating words Figure 2.6 Slide 18 Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA Example: the 1999 Tokaimura nuclear accident

7 Slide 19 Electron Arrangement and the Chemical Properties of Atoms Electrons determine how an atom behaves when it encounters other atoms Electrons orbit the nucleus of an atom in specific electron shells Slide 20 Atoms of the four elements most abundant in life First electron shell (can hold 2 electrons) Outermost electron shell (can hold 8 electrons) Electron Hydrogen (H) Atomic number = 1 Carbon (C) Atomic number = 6 Nitrogen (N) Atomic number = 7 Oxygen (O) Atomic number = 8 Figure 2.7 Slide 21 Chemical Bonding and Molecules Chemical reactions enable atoms to give up or acquire electrons in order to complete their outer shells

8 Slide 22 When an atom loses or gains electrons, it becomes electrically charged Ionic Bonds Sodium atom (Na) Chlorine atom (Cl) Complete outer shells Sodium ion (Na +) Chloride ion (Cl ) Sodium chloride (NaCl) Figure 2.8 Slide 23 Covalent Bonds A covalent bond forms when two atoms share one or more pairs of outer -shell electrons Figure 2.9 Slide 24 Chemical Reactions Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones Hydrogen gas Oxygen gas Water Reactants Products Unnumbered Figure 2.1

9 Slide 25 WATER AND LIFE Life on Earth began in water and evolved there for 3 billion years Slide 26 The abundance of water is a major reason Earth is habitable Figure 2.10 Slide 27 The Structure of Water Studied in isolation, the water molecule is deceptively simple H H O Unnumbered Figure 2.2

10 Slide 28 But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen (+) (+) ( ) ( ) Figure 2.11a Slide 29 The polarity of water results in weak electrical attractions between neighboring water molecules (+) ( ) (+) ( ) ( ) Hydrogen bond (+) ( ) (+) (b) Figure 2.11b Slide 30 Water s Life-Supporting Properties The polarity of water molecules and the hydrogen bonding that results explain most of water s life-supporting properties

11 Slide 31 The Cohesion of Water Water molecules stick together as a result of hydrogen bonding Microscopic tubes Figure 2.12 Slide 32 Surface tension is the measure of how difficult it is to stretch or break the surface of a liquid Figure 2.13 Slide 33 How Water Moderates Temperature Because of hydrogen bonding, water has a strong resistance to temperature change

12 Slide 34 Heat and temperature are related, but different Water can absorb and store large amounts of heat while only changing a few degrees in temperature Slide 35 Water can moderate temperatures Figure 2.14 Slide 36 The Biological Significance of Ice Floating When water molecules get cold, they move apart, forming ice

13 Slide 37 The density of ice is lower than liquid water Hydrogen bond Ice Stable hydrogen bonds Liquid water Hydrogen bonds constantly break and re-form Figure 2.15 Slide 38 Since ice floats, ponds, lakes, and even the oceans do not freeze solid Slide 39 Water as the Solvent of Life A solution is a liquid consisting of two or more substances evenly mixed Ion in solution Salt crystal Figure 2.16

14 Slide 40 When water is the solvent, the result is called an aqueous solution Slide 41 Acids, Bases, and ph Acid Base Slide 42 To describe the acidity of a solution, we use the ph scale Basic solution Neutral solution Oven cleaner Household bleach Household ammonia Milk of magnesia Seawater Human blood Pure water Urine Tomato juice Acidic solution Grapefruit juice Lemon juice; gastric juice ph scale Figure 2.17

15 Slide 43 Buffers are substances that resist ph change Biological fluids contain buffers Buffering is not foolproof Example: acid precipitation Figure 2.18 Slide 44 EVOLUTION CONNECTION: EARTH BEFORE LIFE Chemical reactions and physical processes on the early Earth created an environment that made life possible Slide 45 Earth began as a cold world when gravity drew together dust and ice about 4.5 billion years ago The planet eventually melted from heat produced by compaction radioactive decay impact of meteorites

16 Slide 46 The first atmosphere was probably composed of hot hydrogen gas This gas escaped because the gravity of Earth was not strong enough A new atmosphere was formed from the gases belched from volcanoes H 2 O, CO, CO 2, N 2, CH 4, & NH 3 Seas formed from rain produced by condensation when the earth cooled Figure 2.19 Chapter 2 Study Objectives 1. Explain how and why humans expose themselves to fluoride. 2. List and give an example of the level of biological organization by starting with an ecosystem and ending with atoms. 3. Distinguish between matter, chemical elements, and compounds. Give examples of each. 4. Describe the relative size, location, and electrical charge of protons, neutrons, and electrons within an atom. Explain how the atomic number and mass number are determined. 5. Define an isotope, and explain how isotopes are used in biological research and medicine. 6. Explain how the location of electrons determines the chemical properties of an atom. 7. Distinguish between ionic and covalent chemical bonds. 8. Write the chemical formula for the creation of water from hydrogen and oxygen, and identify the reactants and products. 9. Describe the structure of water, and explain how this shape makes water a polar molecule. 10.Describe the four life-supporting properties of water, and give an example of how each property affects some form of life. 11. Distinguish between the chemical properties of acids, bases, and neutral solutions. Explain how buffers stabilize the ph of acidic and basic solutions. 12. Describe the atmospheric conditions that likely existed on Earth when life first evolved billion years ago.