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Lecture 2

BSC 108 Lecture 2: Biology Chapter 2 Notes

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Biological Sciences
BSC 108
Christina Yates

Biology Chapter 2 Notes Elements and Atoms • Element: substance which cannot be broken down into other substances by chemical reactions • 92 naturally occurring elements (103 total) • Atom: the smallest unit of an element that has all its properties Elements in Organisms • Most Common ➢ Hydrogen – H (9.5%) ➢ Carbon – C (18.5%) ➢ Nitrogen – N (3.3%) ➢ Oxygen – O (65%) ➢ Phosphorus – P ➢ Sulfur – S • Others ➢ Sodium – NA ➢ Potassium – K ➢ Iron – Fe ➢ Magnesium – Mg ➢ Calcium – Ca ➢ Chlorine – Cl • Trace elements are essential for life ➢ An iodine deficiency causes goiter Fluoride In The Water • There has been a sharp decline in tooth decay in the last few decades ➢ Fluoride-containing chemicals have been added to drinking water and dental products • The use of fluoride in drinking water illustrates the point that organisms are chemical systems Harmful • Some elements are harmful to life ➢ Ex: Cadmium o Has been found in some children’s trinkets o A known carcinogen Subatomic Particles in Atoms • Protons: positively charged • Neutrons: no charge • Electrons: negative charge ➢ e’ Characteristics of Atoms • Protons and neutrons in nucleus • Electrons orbit, may occupy different energy levels • Elements differ in the number of subatomic particles in their atoms ➢ The number of protons = the atomic number ➢ An atom’s mass number (atomic weight) = protons + neutrons ➢ In a neutral atom the number of electrons = number of protons Isotope • Isotopes of an element contain different numbers of neutrons • Radioactive isotopes: the nucleus decays, giving off particles and energy • Uncontrolled exposure to radioactive isotopes can harm living organisms by damaging DNA ➢ Ex: the April 26, 1986 Chernobyl nuclear accident ➢ Near accident on March 22, 1975 at Brown’s Ferry NR in Athens, Alabama The Process of Science: Can Alzheimer’s Disease Be Detected Early? • Alzheimer’s disease is a devastating illness. ➢ It gradually destroys a person’s memory and ability to think. • Radioactive isotopes have many uses in research and medication. ➢ Example: PET scans o Used in an attempt to diagnose Alzheimer’s disease before the onset of symptoms. Electrons • Electrons are in orbitals in different energy levels st ➢ 1 sndll has 2 electrons ➢ 2 shell has 8 electrons ➢ 3 shell has 8 electrons Energy • Energy is the capacity to do work; make a change in matter • Joining atoms or breaking up molecules take energy • Potential energy: stored energy ➢ Stored in the bonds that hold atoms together • Kinetic energy: doing work ➢ When electrons move to a lower energy level energy is released ➢ Kinetic energy is released when bonds that hold atoms together are broken Bonds • Ionic bonds: attraction between positive and negative ions ➢ • Ion: element that has gained or lost an electron Covalent Bond • Covalent bonds: sharing electrons between atoms • Hydrogen and oxygen combine to form water • Single Bonds: sharing of one pair of electrons ➢ H-O-H, -C-C-C- • Double bonds: sharing two pairs of electrons ➢ -C=C- • Covalent bonds are among the strongest bonds Hydrogen Bonds • Unequal sharing of electrons • In the case of water, electrons of hydrogen spend more time near the oxygen atom • Important in biological molecules • The weakest type of bond Chemical Reactions • Cells constantly rearrange molecules by breaking existing chemical bonds and forming new ones. ➢ Such changes in the chemical composition of matter are called chemical reactions Properties of Water • High heat of vaporization ➢ As water evaporates, it cools organisms – sweating (humans), panting (animals), transpiration (plants) • Ice formation ➢ When water freezes, it expands and floats due to the formation of a crystalline structure. ➢ Important to aquatic organisms • Cohesion and adhesion ➢ Cohesion: attraction between like molecules (other water molecules) ➢ Adhesion: attraction between different molecules • High Polarity ➢ Water is a polar molecule ➢ Unequal charge distribution ➢ E- spend more time around 0 than H ➢ Water molecules from hydrogen bonds with one another & other molecules • Solvent ➢ Solution: a liquid that is a homogenous mixture of two or more substances (salt water) o Solvent: the dissolving agent of a solution (water) o So
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