Medicina

AP Biology – Midterm Review


Chapter 2 – The Chemical Context of Life
* Elements -> is a substance that cannot be broken down to another substances by chemical reactions. They are, by the moment, 92 elements; gold, copper, carbon, oxygen, etc. Each one of them has a symbol derivate from Latin or German; Sodium - Na, Oxygen – O, Brome – Br.
* 25 elements out of the 92 areessential for life. (C), (O), (H), and (N) – make up the 96% of living matter.
* Compounds -> is a substance consisting of two or more different elements combined into a fixed ratio. Sodium Chloride (NaCl) is a compound between Chloride, which is a gas, and Sodium is a metal; both together create a salt.
* Subatomic particles -> *The Atom is the smallest unit of matter that stillretains the properties of an element; these tiny matter are composed of smaller parts, called subatomic particles.
* Neutrons- they don’t carry any electric charge.
* Protons- they carry positive charge. They’re located in the nucleus with the neutron; their mass, together, is close to 1 Dalton.
* Electrons- they carry negative charge. They’re located in the orbital of an atom; their mass isabout 1/2000.

* Isotopes-> occurs when an atom posses more neutrons than the other atoms of the same element. 126C, 136C…
* Radioactive isotope-> is one in which the nucleus decays spontaneously, giving off particles and energy.
* Covalent vs. ionic bonding ->
* A Covalent Bond is the sharing of a pair of valence electrons by two atoms. Double bondoccurs when is required two atoms to satisfy the requirements of the valance shell; H2O, are two H with 1 atom to gives and O needs 2 atoms to fulfill the valance shell. Electronegativity it’s the attraction of a particular kind of atom for the electrons of a covalent bond. Nonpolar covalent bond occurs when two atoms through a double bound share their electrons equally; while Polar covalent bondsare those whose electrons are not shared equally.
* An Ionic Bond occurs when an anion and a cation attract each other. Salts are the compounds formed through this bond.

Chapter 3 – Water and the Fitness of the Environment
* Importance of hydrogen bonding -> Hydrogen bonds are extremely important in biological systems. Their presence explains many of the properties of water. Theyare used to stabilize and determine the structure of large macromolecules like proteins and nucleic acids. They are involved in the mechanism of enzyme catalysis
* Four emergent properties of water -> cohesion behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent.
* Effects of pH -> the pH of a solution is defined as the negativelogarithm of the hydrogen concentration: pH= -log[H+].
pH declines as H+ concentration increases. OH- = Basic 8-14, [H+] = [OH-] neutral 6-8, H+ = Acidic 0-6
* The pH maintains the enzymes working at the perfect pH concentration for them; but it can deactivate the enzyme if the concentration is higher or lower.
* The pH controls the soil of plants; changing their colors, growth or reproduction.* Acidic rains
* Buffers -> are substances that minimize changes in the concentration of H+ and OH- in a solution. They do so by accepting hydrogen ions from the solution when they are in excess and donating hhydrogen ions to the solution when they have been depleted.

Chapter 4 – Carbon and the Molecular Diversity of Life
* Properties of carbon -> Carbon provide theframework for all tissues of plants and animals. These tissues are built of elements grouped around chains or rings made of carbon atoms. Sugar, and starch are compounds of carbon with hydrogen and oxygen. Proteins such as hair, meat, and silk contain carbon and other elements such as nitrogen, phosphorus, and sulfur.
* Bonding -> a carbon atom contains 2 electrons in its first shell and 4...