BIOL 235 Midterm 2 (version A) exam study guide solution Athabasca Universities STUDY GUIDE NOTES

BIOL 235 Midterm 2 (version A) exam study guide solution Athabasca Universities STUDY GUIDE NOTES Chapter 2 objectives After completing this chapter, you should be able to 1. Identify, by name and symbol, the principal chemical elements of the human body. -Oxygen (O): part of water and many organic (carbon-containing) molecules; used to generate ATP, a molecule used by cells to temporarily store chemical energy -Carbon (C): forms backbone chain and rings of all organic molecules – carbs, lipids, proteins and nucleic acids (DNA and RNA) -Hydrogen (H): part of water and most organic molecules; ionized form H+ makes body fluids more acidic -Nitrogen (N): part of all proteins and nucleic acids -Calcium (Ca): contributes to hardness of bones and teeth; ionized form (Ca2+) needed for blood clotting, release of some hormones, contraction of muscle, and many other processes -Phosphorus (P): part of nucleic acids and ATP; required for normal bone and tooth structure -Potassium (K): ionized form (K+) is the most plentiful cation (+ charged particle) in intracellular fluid; needed to generate action potentials -Sulfur (S); part of some vitamins and many proteins -Sodium (Na): ionized form (Na+) is the most plentiful cation in extracellular fluid; essential for maintaining water balance; needed to generate action potentials -Chlorine (Cl): ionized form (Cl -) is the most plentiful anion (- charged particle) in extracellular fluid; essential for maintaining water balance -Magnesium (Mg): Ionized form (Mg2+) is needed for action of many enzymes, molecules that increase the rate of chemical reactions in organisms -Iron (Fe): Ionized forms (Fe2+ and Fe3+) are part of hemoglobin (oxygen-carrying protein in red blood cells) and some enzymes -Trace elements include: aluminum (Al), boron (B), chromium (Cr), cobalt (Co), fluorine (F), iodine (I), manganese (Mn), molybdenum (Mo), selenium (Se), silicon (Si), tin (Sn), vanadium (V), and zinc (Zn) 2. Describe the basic structure of an atom, ion, molecule and compound. -Atoms are the smallest units of matter that retain the properties and characteristics of the element – hydrogen atoms, the smallest atoms, have a diameter of less than 0.1 nanometers, and the largest atoms are only five times larger -Subatomic particles compose different atoms – there are only 3 that are important in understanding the chemical reactions of the human body: protons, neurons and electrons -Atoms of the same element have the same number of protons – atoms of each element have a unique way of losing, gaining, or sharing their electrons with interacting with other atoms to achieve stability -Ions are electrically charged atoms – ions have positive or negative charges because of an unequal number of protons and electrons – ionization is the process of losing or gaining electrons – this is symbolized by writing the chemical symbol, followed by the number of its (+) or (-) charges – so Ca2+ is a calcium ion that has 2 positive charges because it has lost two electrons / IONS ARE FORMED WHEN ATOMS LOSE OR GAIN ONE OR MORE VALENCE ELECTRONS (positively and negatively charged ions are attracted to each other) -A molecule is the combination of two or more atoms sharing electrons – a molecular formula indicates the elements and the number of atoms of each element that make up a molecule – a molecule can consist of two atoms of the same kind, like in oxygen (O2), - the ‘2’ indicating that the molecule contains two atoms of oxygen -A compound is a substance that contains atoms of two or more different elements –water (H20) and table salt (NaCl) are common compounds – oxygen (02) is not a compound because it consists of atoms of only one element 3. Explain, briefly, how ionic, covalent and hydrogen bonds are formed. -An ionic bond is the force of attraction that holds together ions with opposite charges (opposites attract) – in general, ionic compounds exist as solids, with an orderly, repeating arrangement of ions, such as a crystal of salt – a crystal of salt can be large or small – the number of ions can vary, but the ratio of Na(+) to Cl(-) is always 1:1 – an ionic compound that breaks apart into (+) and (-) ions in a solution is called an electrolyte – Below is a list of the names and symbols of common ions in the body -Below is how table salt is formed BOOM (ions and ionic bond formation) -When a covalent bond forms, two or more atoms share electrons rather than gaining or losing them (they can share 1, 2, or 3 pairs of valence electrons) – the larger number of electron pairs that are shared, the stronger the bond – covalent bonds can be formed between atoms of the same element (molecules) or of different elements (compounds) -A single covalent bond results when two atoms share 1 electron pair (like when a MOLECULE of hydrogen is formed by 2 hydrogen atoms sharing their single valence electrons) -A double covalent bond is formed when 2 atoms share 2 pairs of electrons (like in an oxygen molecule) -A triple covalent bond occurs with 2 atoms share 3 pairs of electrons (like a hydrogen molecule) -The same principles of covalent bonding that applies to atoms of the same element also apply to covalent bonds between atoms of different elements -A nonpolar covalent bond is when two atoms share the electrons equally – one atom does not attract the shared electrons more strongly than the other (the bonds between 2 identical atoms are always nonpolar covalent bonds) -In a polar covalent bond, the sharing of electrons between two atoms is unequal – the nucleus of one atom attracts the shared electrons more strongly than the other – when these bonds forms, the molecule has a partial negative charge near the atom that attract electrons more strongly (this atom has greater electronegativity; the power to attract electrons to itself) – and at least one other atom in the molecule with have a partial positive charge (these partial charges are indicated by a delta symbol followed by a + or -) -A hydrogen bond is made up from polar covalent bonds that form between hydrogen atoms and other atoms – a hydrogen bond forms when a hydrogen atom with a partial positive charge attracts the partial negative charge of electronegative atoms – SOOO hydrogen bonds are formed by attracting oppositely charged parts of molecules, rather than sharing electrons like in covalent bonds or the loss or gain of electrons as in ionic bonds -Hydrogen bonds are weak compared to ionic/covalent bonds, and therefore cannot bind atoms into molecules 4. Define the term “chemical reaction,” and explain the basic differences between synthesis, decomposition, exchange and reversible reactions. -A chemical reaction occurs when new bonds form or old bonds break between atoms – the interactions of valence electrons are the basis of all chemical reactions – for instance, how hydrogen and oxygen molecules react to form water molecules (two H2 and one 02 are known as reactants, the ending substance; 2 molecules of H20 are the products) -The total mass of the reactants is the same as the total mass of the products (the atoms are just rearranged and therefore have different chemical properties) -Metabolism refers to all the chemical reactions occurring in the body -Synthesis reactions is when two or more atoms, ions or molecules combine to form new and larger molecules (synthesis = to put together) – a synthesis reaction can be explained as follows: an example can be the reaction between 2 hydrogen molecules and one oxygen molecule to form two molecules of water – all synthesis reactions that occur in the body are called anabolism (they are usually endergonic because they absorb more energy then they release) -Decomposition reactions split up large molecules into smaller atoms, ions, or molecules -Decomposition reactions that occur in the body are referred to as catabolism – they are usually exergonic because they release more energy than they absorb -Exchange reactions consist of both synthesis and decomposition – they work like the example below (the bonds between A and B and between C and D break, and new bonds then form between A and D and between B and C: AB + CD  AD + BC -Reversible reactions, the products can revert to the original reactants – these reactions are indicated by two half-arrows pointing in opposite directions -In the case where reactions are only reversible under special conditions, whatever is written above or below the arrows is indicates the condition needed for the reaction to occur, for example below – AB breaks down into A and B only when water is added. A and B react to produce AB only when heat is applied. 5. List and compare the properties of inorganic acids, bases, salts and water. -Inorganic compounds usually lack carbon and are structurally simple – their molecules only have a few atoms and they cannot perform complicated biological functions, they include water, many salts, acids and bases – they may have either ionic or covalent bonds – water makes up 55-60% of an adult’s body mass -Organic compounds always contain carbon, usually contain hydrogen, and always have covalent bonds – most are large molecules, and many are made up of long chains of carbon atoms – they make up 38-53% of the human body -Hydrophilic solutes are charged or contain polar covalent bonds, which means they dissolve easily in water – examples of this are sugar and salt -Hydrophobic molecules contain mainly nonpolar covalent bonds – they are not very soluble, examples include animal fats and vegetable oils -When a crystal of salt (NaCl) dissolves in water, the electronegative oxygen atom in water molecules attracts the sodium ions (Na+), and the electropositive hydrogen atoms in water molecules attract the chloride ions (Cl-) – soon water molecules surround and separate Na+ and Cl- ions from each other, breaking the bonds that held the NaCl together – the water molecules surrounding the ions also lessen the chance the Na+ and CL- will come together and re-form an ionic bond -Hydrolysis is the addition of water molecules to aid in breaking down molecules – hydrolysis reactions enable dietary nutrients to be absorbed into the body -Dehydration synthesis reaction: when two smaller molecules join to a larger molecule and a water molecule is one of the products formed -Water has a high heat capacity because it can absorb or release a large amount of heat with only a modest change in its own temperature – it has this capacity because of the large amount of hydrogen bonds in water – as water absorbs heat energy, some of the energy is used to break hydrogen bonds – less NRG is left over to increase the motion of H20 molecules, which would increase the temperature -Water is a major component of mucus and other lubricating fluids in the body when internal organs touch and slide over one another – it is also needed for joints, where bones, ligaments and tendons rub against one another – it also moistens food in the gastrointestinal tract to aid in digestion -A mixture is a combination of elements or compounds that are physically blended together but not bound by chemical bonds – like the air you are breathing, which is a mixture of gases – 3 common liquid mixtures are solutions, colloids and suspensions – once mixed together, solutes in a solution remain evenly spread among solvent molecules, and because solute particles are small, a solution looks transparent -A colloid has particles large enough to scatter in light (like how water droplets in fog scatter light from headlights) – for this reason, colloids usually appear translucent or opaque, like milk! It is both a colloid and a solution – the large milk proteins make it a colloid, whereas calcium salts, milk sugar (lactose), ions, and other particles are in solution -Solutes in both solutions and colloids do not settle out and accumulate at the bottom -In a suspension (by contrast), the suspended material might mix with the liquid or suspending medium for a moment, but it will eventually settle out (like blood) -Dissociation is when inorganic acids, bases, or salts dissolve in water (they separate into ions and become water molecules) -An acid is a substance that dissociates into 1 or more H ions (H+), and 1 or more anions – because H+ is a single proton with 1 positive charge, an acid is referred to as a proton donor -A base removes H+ form a solution and is therefore a proton acceptor -As seen in the picture below, many bases dissociate into 1 or more hydroxide ions (OH-) and 1 or more cations -A salt, when dissolved in water, dissociates into cations and anions, neither of which is H+ or OH- -In the body, salts (like potassium chloride) are electrolytes that are important for carrying electrical currents in nerve and muscular tissues -Acids and bases react with one another to form salts 6. Define the term “pH,” and explain the role of buffer systems in homeostasis. -To ensure homeostasis, intracellular and extracellular fluids must contain almost balanced quantities of acids and bases – the more hydrogen ions (H+) dissolved in a solution, the more acidic it is, whereas the more hydroxide ions (OH-), the more basic (alkaline) it is – any change from the narrow limits of normal H+ and OH- concentrations greatly disrupts bodily functions  -A solution’s acidity or alkalinity is rated on the pH scale (o-14) – a change of one whole number of the pH scale represents a tenfold change in the number of H+ (i.e. a pH of 6 denote 10x more H+ than a pH of 7) 7. Compare the structure and functions of carbohydrates, lipids, proteins, DNA, RNA and adenosine triphosphate (ATP). -Important categories of organic compounds include carbs, lipids, proteins, nucleic acids, and adenosine triphosphate (ATP) -Organic compounds are usually