domingo, 18 de septiembre de 2011

Biology - Chapter 6 Notes

Section 1: Atoms and their Interactions
I. Elements
A. Natural elements in living things
1. everything is made of these substance
2. Of all the naturally-occurring elements in life, only about 25 are essential for the human body
3. Carbon, hydrogen, oxygen and nitrogen make up about 96% of the mass of the human body
4. Symbols
a. Each element is identified by a one or two letter abbreviation called a symbol
b. C represents carbon, Ca represents calcium, etc.
B. Trace elements
1. These are elements in the human body that are present in very small amounts
2. They play a vital role in maintaing the body healthy
3. Plants obtain them from the ground and then animals eat those plants
II. Atoms: the building blocks of Elements
A. The structure of an atom
1. All atoms have the same general structure
a. The nucleus is the center of the atom
i. these contain protons, which are positively charged
ii. also contain neutrons, which have no charge
b. The region of space that surrounding the nucleus contains electrons; it is called the electron cloud
B. Electron energy levels
1. The electron cloud is divided in energy levels
a. the first level can can hold only two electrons
b. the second level can hold a maximum of eight electrons
c. the third level can hold up to 18 electrons
2. Atoms contain equal numbers of electrons and protons; their charge remains neutral
III. Isotopes of an Element
A. Isotopes are atoms of the same element that have different numbers of neutrons
B. They are useful to scientists
1. The nuclei of some isotopes are unstable and tend to break apart giving radiation; they are radioactive
2. Since radiation is detectable, scientists have found medical uses
IV. Compounds and Bonding
A. Compounds: they are substances of atoms composed of two or more elements
B. Formation of covalent bonds
1. Happens when two atoms share electrons 
2. Sugars, fats, proteins and others have covalent bonds
3. A molecule is a group of atoms held together by this type of bonds
B. Formation of ionic bonds
1. Happens when atoms lose or gain electrons
2. An ion is a charged particle made of atoms
3. An ionic compound is the attractive force between two ions of opposite charges
V. Chemical Reactions
A. These occur when bonds are formed or broken, causing substances to recombine into different substances
B. All of the chemical reactions that occur within an organism are the metabolism
C. Writing chemical equations
1. A reactant is a substance that undergoes a chemical reaction
2. A product is a substance created by a chemical reaction
3. The number before each chemical formula indicates the number of molecules of each substance
4. A molecule of sugar could be represented like this: C₁₂H₂₂O¹¹
VI. Mixtures and Solutions
A. Mixture: a combination of substances in which the individual components maintain their properties
B. Solution: a mixture in which one or more substances (solutes) are distributed evenly in another substance (solvent)
C. Acids and bases
1. A chemical reaction will depend on:
a. temperature
b. available energy
c. concentration of a substance
d. pH of the environment within the organism
i. pH is a measure of how acidic or basic a solution is
1. Acids: any substance that forms hydrogen ions in water
a. a substance is acidic with a pH below 7
b. many fruits like oranges and grapefruits are acidic 
2. Bases: any substance that forms hydroxide ions in water
a. a substance is basic with a pH above 7
3. Both are vital to organisms but if they are very strong they can be dangerous

Section 2

Water constitutes 70% to 95% of living things. It is probably the most important compound in organisms. A polar covalent bond is when the atoms are sharing electrons unevenly. More formally, a polar molecule is a molecule with unequal distribution of charge. Water is polar. Because water is polar, it is a good solvent (something that dissolves other substance). A rule for chemistry is: Like dissolves like. This is why polar substances dissolve polar and ionic substances. Water can dissolve practically anything. What water can’t dissolve are non-polar molecules. An example is oil. Negative charges attract. Since non-polar substances have no charge, they are not attracted to anything and can’t be dissolved. A Hydrogen bond is a strong inter-molecular force. Water’s attraction for itself is called cohesion. Water’s attraction for other substances is adhesion. Water resists temperature change. It has a high specific heat, which is the amount of energy required to raise the temperature of one gram of water by one degree celsius. The fact that water is polar is important for us because it helps us dissolve many substances in our blood. It helps to maintain body temperatures as well. Water is one of the few substances that expands when it freezes. 
Scottish scientist Robert Brown discovered the random motion of atoms and molecules in 1827 called now Brownian motion. Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. Diffusion results because of Brownian motion. Dynamic equilibrium is when an area has an equal concentration of a gas throughout. They are three factors that affect the rate of diffusion: concentration, temperature, and pressure. 

Section 3

Every organic molecule has carbon but not every carbon molecule is organic.
Carbon can form:
1. Straight chains
2. Branched chains
3. Rings
It can form this type of bonds:
1. Single 
2. Double 
3. Triple 
A polymer is a large molecule formed when many small molecules bond together.
A carbohydrate is a biomolecule composed of carbon, hydrogen, and oxygen with a ratio of about two hydrogen atoms and one oxygen atom for every carbon atom. 
Plants store carbohydrate as starch.
Animals store them as glycogen. 
Macromolecule (polymer) Basic building Blocks (monomers)
Carbohydrate Monosaccharide
Lipids (non-polar) Fatty acids
Proteins Amino acids
Lipids are large biomolecules that are made mostly of carbon and hydrogen with a small amount of oxygen. 
A protein is a large, complex polymer composed of carbon, hydrogen, oxygen, nitrogen and sometimes sulfur. 
Amino acids are the basic building blocks of proteins. 
Peptide bonds are covalent bonds formed between amino acids. 
Enzymes are important proteins found in living things. It changes the rate of a chemical reaction. They lower the activation energy.
Activation energy is the energy necessary for a chemical reaction to get started. 
A nucleic acid is a complex bimolecular that stores cellular information in the form of a code. 
DNA:
• DeoxyriboNucleic Acid (In nucleus)
RNA: 
• RiboNucleic Acid (In cytoplasm)
A nucleotide are arranged in 3 groups:
1. Nitrogenous base
2. Simple sugar
3. Phosphate group

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