The living world has a hierarchy of organizational levels - from molecules to ecosystems

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2 The living world has a hierarchy of organizational levels - from molecules to ecosystems In order to understand the whole, biologists study the parts (reductionism)

3 With each level, new properties EMERGE as a result of interactions among components at the lower level. emergent properties ***an important BIG PICTURE CONCEPT***

4 The emergence of biological function starts at the chemical level -Everything an organism IS and DOES depends on chemistry -Chemistry is dependent on the arrangement of atoms in molecules

5 An Element cannot be broken down by ordinary chemical means About 25 different chemical elements are essential to life You can memorize and think about the Big 4: OCHN* *i.e. important details*

6 3.1 Atoms The smallest particle of an element is an atom Different elements have different types of atoms An atom is made up of protons and neutrons located in a nucleus The nucleus is surrounded by electrons Each atom is held together by attractions between the positively charged protons and negatively charged electrons Neutrons are electrically neutral Not drawn to scale. Electrons don t orbit like planets.

7 Different elements have different types of atoms Trivial factoids that illustrate this concept: Each gold bar is made up of identical atoms each with 79 protons in their nuclei. A bar of iron is made of identical atoms each with 26 protons in their nuclei.

8 Electrons e- determine the chemical behavior of atoms Fig. 3.1 Electrons are arranged in shells The electrons in the outermost shell determines the chemical properties of an atom

9 Electrons Each electron shell has a specific number of electrons The inner shell holds up to two electrons The outer shells hold up to eight electrons Fig. 3.3 Atoms with incomplete electron orbitals are more reactive

10 Why?

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12 Electrons Energy is the ability to do work Electrons have energy due to their relative orbital position (potential energy) Fig. 3.2

13 3.2 Ions - When atoms gain or lose electrons, charged atoms called ions are created Fig. 3.4

14 3.2 Isotopes Isotopes are atoms with the same number of protons but different numbers of neutrons Fig % of all carbon Different atomic mass Same atomic number

15 Radioactive Isotopes Radioactive isotopes are used in 1. Medicine Tracers are taken up and used by the body Emissions are detected using special lab equipment 2. Dating fossils The rate of decay of a radioactive element is constant The amount of decay can be used to date fossils

16 Fig. 3.7 Radioactive isotope dating

17 3.3 Bonds Atoms are held together by chemical bonds A chemical reaction involves the making and/or breaking of chemical bonds There are three kinds 1. Ionic bonds 2. Covalent bonds 3. Hydrogen bonds

18 Ionic Bonds Formed by the attraction of oppositely charged ions Strong but not as strong as covalent bonds Fig. 3.8 The formation of the ionic bond in table salt

19 Chemical elements combine in fixed ratios to form compounds Example: sodium + chlorine sodium chloride

20 Covalent Bonds Covalent bonds are formed when two atoms share electrons A molecule is a group of atoms held together by covalent bonds Covalent bonds are strong The strength increases with the number of shared electrons Covalent bonds share electrons. Nonpolar covalent bonds share electrons equally. Polar covalent bonds share electrons unequally. Each hydrogen atom shares its single electron with the other. This gives both atoms a filled outer shelland stability.

21 Polar covalent bonds share electrons unequally. The oxygen atom is more electronegative than the hydrogen atoms. It exerts a greater attraction on the shared electrons. The molecule as a whole is polar.

22 Polar or Nonpolar?

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24 Hydrogen bonds Water molecules are polar molecules The molecule has an electron-rich (-) and and electron-poor (+) regions. Hydrogen bonds are formed by the attraction of opposite partial charges between two polar molecules Each hydrogen bond is very weak However, the cumulative effect of enormous numbers can make them quite strong

25 3.4 Hydrogen bonding is responsible for many of the essential properties of water Heat Storage A large input of thermal energy is required to disrupt the organization of liquid water This minimizes temperature changes Ice Formation At low temperatures, hydrogen bonds don t break Water forms a regular crystal structure that floats High Heat of Vaporization At high temperatures, hydrogen bonds do break Water is changed into vapor

26 3.4 Hydrogen Bonds Give Water Unique Properties Cohesion Fig Attraction of water molecules to other water molecules Example: Surface tension Adhesion Attraction of water molecules to other polar molecules Example: Capillary action Water strider

27 3.4 Hydrogen Bonds Give Water High Polarity Unique Properties Polar molecules are termed hydrophilic All polar molecules that dissolve in water are termed soluble Nonpolar molecules are termed hydrophobic These do not form hydrogen bonds and are therefore not water soluble

28 Salt dissolves when all ions have separated from the crystal Fig How salt dissolves in water

29 Hydrogen bonds are weak (only 5% the strength of a covalent bond) but important hold water molecules together hold proteins together hold the two strands of the DNA double helix together

30 3.5 Water Ionizes Covalent bonds within a water molecule sometimes break spontaneously H 2 O OH + hydroxide ion H + hydrogen ion This process of spontaneous ion formation is called ionization It is not common because of the strength of covalent bonds

31 ph A convenient way to express the hydrogen ion concentration of a solution ph _ = log [H + ] The ph scale is logarithmic A difference of one unit represents a ten-fold change in H + concentration Acid Dissociates in water to increase H + concentration Base Combines with H + when dissolved in water

32 Acidic solutions Neutral solutions Balance between H+ and OH Basic solutions Fig The ph Scale

33 Buffers Hydrogen ion reservoirs that take up or release H + as needed The key buffer in blood is an acid-base pair Fig Favored reaction when [H + ] is low H 2 O Water CO 2 Carbon dioxide H 2 CO 3 Carbonic acid HCO 3 Bicarbonate ion H + Hydrogen ion Favored reaction when [H + ] is high