Bio1441 Chapters 2-5 Review Chapter 2: The Chemical Context of Life I. Matter consists of chemical elements in pure form and in combinations called compounds a. Elements and compounds i. Element : substance that cannot be broken down into other substances by chemical rxns (92 that occur in nature) ii. Compound : substance made of 2 or more different elements combined in a fixed ratio 1. Ex: NaCl—1:1, pure Na is metal (corrosive) and Cl is a gas (toxic)—combined they make table salt (emergent properties) b. The elements of life 1. Of the 92 in nature, approx. 25% are essential for life (humans- 25, plants- 17) 2. Humans: C, H, O, and N make up 96.3% of living matter; Ca, P, K, S, Cl, Mg = 3.7% ii. Trace elements : needed in small quantities 1. Ex: Fe needed in all lifeforms 2. Ex: vertebrates need iodine b/c it is essential to hormones produced by the thyroid gland (goiter—enlarged gland due to iodine deficiency) c. Evolution of tolerance to toxic elements i. Ex: serpentine plants—can survive in enviro with heavy cobalt, chromium, and nickel deposits II. An element’s properties depend on the structure of its atoms i. Atom : smallest unit of matter that still retains the properties of an element 1. Charge is neutral (protons = electrons) unless indicated otherwise b. Subatomic particles i. Neutrons : no charge, found in nucleus, approx. 1 Dalton ii. Protons : positive, found in nucleus, approx. 1 Dalton iii. Electrons : negative, surround nucleus in a cloud and travel at speed of light (centrifugal force), approx. 1/2000 th Dalton c. Atomic number and atomic mass i. Atomic number : number of protons (and electrons if neutral), written as subscript to the left-down of an element (Ex: 2 He) ii. Mass number : sum of protons and neutrons, written as subscript to the left-up of the element ( 23 11 Na—mass number is 23 [protons + neutrons] and atomic number [protons] is 11 so 23-11= number of neutrons = 12 iii. Atomic mass : total mass (only slightly more than mass number because electron mass is negligible) d. Isotopes : different number of neutrons of same element i. Ex: carbon-12 ( 12 6 C) which is 99% of carbon in nature and has 6 neutrons; 12 C (6 neutrons) and 13 C (7 neutrons) are stable isotopes (their nuclei don’t tend to lose subatomic particles—a process called decay ); 14 C (8 neutrons) is radioactive (unstable) ii. Radioactive isotope : one in which the nucleus decays spontaneously, giving off particles and energy; when radioactive decay leads to a change in number of protons, it transforms the atom to an atom of another element (neutron splits into 1 electron and 1 proton) 1. Ex: 14 C (6 protons) decays and becomes 14 N (7 protons) 1
Bio1441 Chapters 2-5 Review e. Radioactive tracers: radioactive isotopes usually used as diagnostic tools in medicine i. Cells use radioactive atoms same as non-radioactive isotopes of same element; radioactive isotopes are incorporated into biologically active molecules which are then used as tracers to track atoms during metabolism 1. Ex: certain kidney disorders diagnosed by injecting small amount of radioactively
You've reached the end of your free preview.
Want to read all 16 pages?
- Fall '09