Electrons are negatively charged particles that act as carriers of energy.

Electrons are attracted to the nucleus. This attraction makes it possible for the electrons to move constantly around the nucleus.

D. Electrons

Properties of a compound are usually dissimilar from properties of its elements. Take for example NaCl. Na (sodium) is a silver-colored metal that is very soft. It reacts with water quit explosively. Chlorine is poisonous and reactive yellow gas that was used as a weapon in World War I. These two elements form a compound NaCl, known as table salt, which is not toxic, water soluble and necessary for proper functioning of living being’s organism.

Isotopes of an element differ in the number of neutron they contain. They have same chemical properties but different masses.

Three main subatomic particles are protons, neutrons and electrons. Protons have positive charge, neutrons don’t have any charge and electrons have negative charge.

Van der Waals forces might be strong enough to hold two molecules together if two molecules have matching shapes that fit together and are positioned on small distance.

When two atoms form a covalent bond, each of them contributes one electron to form a pair of electrons. Atoms that form covalent bond are approximately equal in their ability to draw electrons towards themselves and that would lead to more or less equal shared electron pair. Therefore, you can conclude that due to similar ability for traction of electrons, nonmetals are elements that in mutual reaction form covalent bond.

b. hydroxide ions

c. hydrogen bonds

Generally, function of buffer is to prevent sharp and sudden changes in pH while reacting with strong acids or bases. Function of bicarbonate ions as a buffer in blood is to maintain pH of blood thanks to balance in concentration of carbonic acid, bicarbonate ion and carbon dioxide. Failure of this system’s function would lead to acid-base imbalance in the blood, such as acidemia (pH7.45).

pH scale measures the concentration of H+ ions in a solution.

Thanks to ability to form multiple hydrogen bonds, water molecule is able to dissolve many other substances.

The difference between the solute and solvent is that solute is substance that is dissolved and the solvent is the substance-often liquid in which solute is dissolved. The most common solvent is the water, and solute can be lemon juice in lemonade.

Water is essential for all living things because of its polarity which allows forming ice that is denser than water itself and that allows life under the ice. Also, a big percent of human body is composed of water (around 60%), so if adequate intake of water is maintained during the day, living organisms can function properly. Due to its characteristics, water a solvent to many other substances and has ability to regulate metabolism which makes it necessary for living cells.

b. nitrogen, sulfur, phosphorus

d. nucleic acids

b. proteins

Monomers, when joined together form the polymers. Polymers are made up of monomers, which means that they have the same composition.

Proteins are composed of amino acids that are joined by peptide bonds.

Proteins have three major functions:

1. Proteins transport substances into and out of the cells

2. Proteins provide structural support.

3. Proteins help in metabolism.

General structure of amino acid is a compound of carbon atom in the center with an amino group (-NH2) and a carboxyl group (-COOH) on opposite sides. Also, on upper side of carbon atom is hydrogen atom and on its opposite side is R group which can be various, depending on specific properties of amino acid.

Nucleotides are basic units of nucleic acid. Every nucleotide consists of 5-carbon sugar, a phosphate group and a nitrogenous base. A Sugar component determines type of nucleic acid: ribose for RNA and deoxyribose for DNA. A Phosphate group (-PO4) is significant for creating the sides of the DNA ladder. Nitrogenous bases are classified in two groups: purines and pyrimidines. Purines are Adenine (A) and Guanine (G) and pyrimidines are Cytosine (C), Guanine (G) and Uracil (U).

a. enzymes

b. chemical bonds

**Exothermic reaction** (heat-releasing) tends to occur spontaneously as energy in the form of heat is released. It does not require high activation energy to occur unlike an energy-absorbing reaction or *endothermic reaction*.

**Endothermic reaction** (heat-absorbing) does not occur spontaneously most of the time unlike exothermic because the energy it requires must be met first.

Energy-releasing reaction or exothermic reaction

The amount of energy needed for starting a reaction is called activation energy.

Enzymes act as catalysts by lowering activation energy and in that manner speed up reactions. In other words, they accelerate a chemical reaction without interference its equilibrium.

Activity of enzymes is sensitive on environment changes. Factors that affect quality of enzymatic reactions are temperature, pH, enzyme concentration, substrate concentration and presence of inhibitors or activators.

Oxygen atom has eight protons in the nucleus. Due to the same number of protons and electrons in an element (Oxygen in this case), we can conclude that oxygen atom has 8 electrons. The number of neutrons varies and it can be calculated from the atomic weight. Since the atomic weight of oxygen is 16 and weight of the protons and neutrons is particularly the same (about one), in order to get neutron number, you should subtract 8 from 16. Therefore, oxygen has 8 protons, 8 neutrons and 8 electrons.

In diagram below, there is reaction of dissolving table salt (NaCl) as a solute on positive (Na+) ion and negative (Cl-) ion in water which is a solvent. This mixture is called solution because the ions progressively dissolve and create solution with evenly distributed components.

By identifying the properties of water, you cannot predict or infer the properties of its component elements. Water belongs to the compounds and they usually have different properties then compound elements itself. For example, water is a liquid that puts fires away unlike its elements, oxygen and hydrogen which are flammable gases.

The four major biomolecules are carbohydrates, proteins, nucleic acids, and lipids. All of them have carbon bases in their structures.

– **Carbohydrates** are made of 1 carbon, 2 hydrogen, and 1 hydrogen atomic ratio, most of the time. Carbohydrates are used as storage of energy like glucose. These are also used for structural support (cellulose) and protection.

– **Proteins** are composed of carbon, hydrogen, oxygen, and nitrogen. These are the base or polymers of amino acids that have an amino group at one end and a carboxyl group at the other end. Proteins are important in cellular regulation, transport, and immunity.

– **Nucleic acids** are composed of a 5-carbon sugar, phosphate group, and a nitrogenous base. These are important components of the genetic material DNA and RNA.

– **Lipids** are mostly composed of carbon and hydrogen atoms. These are not soluble in water. These are great energy storage, chemical messengers, lipid membranes, and covering.

One experiment would be testing substance’s ability of dissolving in water. If white solid substance dissolves in water, that would be carbohydrate in this case because lipids are not water soluble. If we want to test white substance solubility in organic solvents such as ethanol, we could get two outcomes. If it dissolves that could be a lipid or a carbohydrate because of hydrogen bonding between molecules in solution. It we want to prove lipid solvency in this type of experiment we should use non polar organics like benzene or hexane. Glucose can’t dissolve in them because of opposing polarities of the solvents.

In cellular respiration process, glucose is broken down in carbon dioxide and water in presence of oxygen. Energy is released and captured by ATP molecule. In reverse process, that is called the oxidation of glucose, energy is required to start the reaction between carbon dioxide and water, mostly by sunlight. Products of this reaction are glucose molecules and oxygen. This type of reaction is obtained by plants as typical way of carbohydrates production. But, there is a difference in maintaining this process in humans and animals due to their inability for photosynthesis process. So, they obtain their energy from reverse process, degradation of glucose to carbon dioxide and water.

Average body temperature for humans is in range from 36.1 to 37.2. Constant body temperature is crucial for normal body function. Enzymes as catalysts play an important role in maintaining homeostasis of living organism. Thanks to their unique function-acceleration of chemical reactions, vital processes are performed more quickly and more successful. Important factor in their proper functioning is keeping of constant body temperature. With temperature rising, hydrogen bonds weaken which causes unfold of proteins and active site structure disrupting. Active site structure has to be intact because enzyme activity depends upon it.

Sugar molecules (carbohydrates) contain carbon, hydrogen and oxygen atoms. Their hydrocarbon backbones are parts of amino acids and other molecules based on carbon atom that can be gathered to form other large molecules (such as proteins or DNA molecule). Necessary elements for this reaction are carbon, hydrogen and oxygen because these elements are mutual for both reactants.

Carbon dioxide is important metabolite for every living organism. It is soluble compound which makes it easy to diffuse in and out of the cell. Unlike carbon dioxide, bicarbonate must be transported. Reaction of carbon dioxide and water as reactants gives hydrogen ion and bicarbonate as a product. This reaction is very important and it is easily maintained with action of carbonic anhydrase. The conversion of bicarbonate to carbon dioxide and vice versa facilitates bicarbonates transport into the cell as well as trapping of carbon dioxide in the cell. In physiological pH this reaction is slowly proceeds, so organism produce enzymes as an improvement of reaction velocity. Depending on what is needed, the active site of this enzyme can exist in two forms a high pH form that is active in the hydration of carbon dioxide and a low pH that is active in dehydration of bicarbonate. For best outcome, temperature of equilibrium is very important. Because the optimal temperature for enzyme’s reaction is in range of 35 to 40 degrees of Celsius, the best temperature value would be 37 degrees. Therefore, the plan for an investigation would be taking of 5 samples heated to exact degrees in range of 35 to 40, with adequate amount of enzyme and observing speed of reaction and how fast will product appear.

Enzymes have an exact place for bonding with substrates called the active site. The active site is characteristic because it has specific shape for every enzyme and that allows substrate to be held with it thanks to weak bonds such as hydrogen bonds and van der Waals forces. Changing of environmental factors like temperature and pH rising or decreasing, weaken hydrogen bonds which change the active site structure and therefore causes unfold of proteins. Changing of these factors also causes increasing values of activation energy and enzymes’ speeding of reaction is missing. That leads to disturbance of homeostasis in living organism.

For starters, high heat capacity of some substance represents the ratio of the amount of heath that is transferred to an object which consequently increases its temperature. Because of this process, substance’s molecules move faster. Water’s heath capacity is relatively high thanks to hydrogen bonding. This allows oceans and lakes to absorb great amounts of heat with slight changes in water temperature. Therefore, living organisms in water are protected from sudden and drastic temperature changes.

Water is so called “universal solvent” because it dissolves the biggest number of substances among solvents. This is important characteristic because it collects and releases valuable substances like minerals and nutrients either through ground or human body. This is possible because of hydrogen bonds which allow water’s polarity.

Burning log is form of exothermic oxidation reaction that occurs in very fast rate. An inundation of electrons from a mass of fuel ions become ions with a lower oxidation state with releasing of heat and light throughout. Ions are atoms in compounds with chemical relatively low energy potential, and fuels are capable of electrons donation and oxidants have tendency for receiving electrons. But the problem is low potentials of the both reactant sides and released energy has to go somewhere: in appearance of heat and light. Heat is released due to increased kinetic energy of surrounded molecules and light due to emitted photons from electrons excitation. In burning log example, the fuel is carbon in the wood and the oxidant is oxygen from the air. In the beginning both of the atoms are stable. For this reaction to start, a missing piece is the outer energy source like an initial spark for example. Released energy causes reactant atoms to form chain reaction which lasts till last converted atom of carbon monoxide. Then, the fire dies.

Antacids are medications used for reducing excess stomach acid in order to relieve symptoms such as sour stomach, heartburn and acid ingestion. This is possible thanks to chemical reaction of neutralization where antacids as bases neutralize HCl. Stomach produces acid to kill bacteria and to help with digestion. Because of its corrosive properties, body forms a natural mucus barrier which has protective function that protects stomach from being eroded. Due to some factors, HCl can be excreted too much or for some reasons barrier could be broken. That allows acid to damage the lining tissue. If any of these conditions occurs, antacids are indicated.

In the shown table, we can observe six different Carbon isotopes. Due to the variation of their proton number, their stability change. Carbon Isotope 10, 11 and 15 have very short half life because of their imbalance of neutron and proton numbers. Carbon 12 is the most stable because of the same number of neutrons and protons in its nucleus. Abundance is very high and half life is stable. Carbon 13 has one neutron more comparing to the proton number, but it still ensures certain stability. The biggest difference occurs in Carbon 14. Its 8 protons make it very unstable and it disintegrates or goes through radioactive decay which provides it very long half life-5270 years. Carbon 12, 13 and 14 are only carbon isotopes naturally occurred.

Among the six isotopes in this table, the most useful for labeling or tracing would be isotope Carbon-14 because its half life is the longest in list. That means that it takes the longest time to fall to half its original value. Therefore, it will hold on the longest in organism and it will be the easiest to track.

Carbohydrates are macromolecules made upon carbon, hydrogen and oxygen often arranged in ratio 1:2:1. Due to this formula, we can determine number of atoms in complex carbohydrates. If we take, for example, complex carbohydrate with 12 carbon atoms, with previous mentioned ratio we can calculate that it has 12 carbon atoms, 24 hydrogen atoms and 12 oxygen atoms.

Number of protons

Number of electrons

Hydrogen atom (H)

1

1

Oxygen atom (O)

8

8

Water molecule (H2O)

10

10

Hydrogen ion (H+)

1

0

Hydroxide ion (OH-)

9

10

Atoms of hydrogen and oxygen have equal number of electrons and protons in their nuclei: hydrogen has 1 electron and 1 proton while oxygen has 8 protons and 8 electrons. In water molecule, there are two atoms of hydrogen and 1 atom of oxygen which gives it 10 proton and 10 electrons. Change happens when water molecule separates on hydrogen ion (H+) and hydroxide ion (OH-). While separating, high electron attraction of oxygen atom pulls hydrogen’s electron and attach it to hydroxide ion. Therefore, hydrogen ion has 1 proton and zero electrons, which makes it positively charged, while hydroxide ion has 9 protons and 10 electrons which makes it negatively charged.

Method of classifying could be depending on the existing functional group. Functional groups have an important role in formation of macromolecules. Each type of macromolecules has its own type of functional group. They are: hydroxyl, methyl, carbonyl, amino, phosphate and sulfhydryl group. The functional groups determine the shapes of macromolecules which determine their function. Different functional groups have different bonds inside of macromolecule. That defines properties of macromolecules. Carbohydrates structure can vary from simple carbohydrates with one carbon atom, two hydrogen atoms and one atom of oxygen to complex carbohydrates with chain formation. For example, glucose in starch and in cellulose has different configurations and different purposes. Lipids can have different formations depending on bonds between them. If there is a single bond between carbon atom and fatty acid chain, lipid is saturated. But, if there is at least carbon-carbon double bond that is unsaturated fatty acid. They also have influence on bond’s polarity. Lipids are made upon hydrophilic (head) and hydrophobic part (tail). Due to this characteristic, lipids can form double layered membranes. Nucleic acids are composed of nucleotides which are made upon a 5-carbon sugar, a phosphate group and a nitrogenous base. Sugar component of them determines type of nucleic acid and its function besides it. Proteins include amino acids consisted of amino and carboxyl group on opposite ends as well as bond with hydrogen atom and R group. R group specifies type of amino acids and their function.

Enzymes have very important roles in proper functioning of living organism. They are catalysts of chemical reactions which speed up the rate of chemical reaction by lowering of activation energy. Also, they show absolute specificity for catalyzing only one particular reaction thanks to unique shape of the active site (place where enzyme and substrate meets and they have to be complementary). In case of carbonic anhydrases, the most of them are classified as metalloenzymes because their active site mostly contains a zinc ion. Carbonic anhydrase regulates pH and balance of fluids. It catalyzes the reaction between carbon dioxide and water. This enzyme has significant role in transportation of carbon dioxide and production of carbon acid in the stomach lining.

Water is essential for living things because a lot of irreplaceable properties. Some of those are heat capacity, water molecule’s polarity and adhesion.
Heat capacity represents amount of energy caused by faster moving of molecules of some substance in order to raise its temperature. Water’s heat capacity is quite high because of hydrogen bonding. Consequently, temperature in lakes and oceans is changing gradually. Because of this quality, protection of living organisms in water is guaranteed from drastic temperature changes.
Polarity of water molecule is enabled due to negative and positive charge on different parts of a molecule. This allows forming of multiple hydrogen bonds and attracting great number of molecules bond together. During the winter, water freezes on temperature below 0 degrees of Celsius. However, while freezing water molecules extend themselves as much as they can and hold together with hydrogen bonds. Therefore, ice floats in water because of its lower density. Polarity also explains water’s great dissolution ability which is essential for living beings.
Adhesion is ability of attracting molecules of different substances. Adhesion makes capillary action possible because water’s molecules form stronger bond with some other molecules than between themselves. This quality among some others, allows drawing water out of its roots and nutrition of its stems and leaves.

Macromolecules are large molecules made upon polymers and polymers are molecules formed by monomers connection. In the process of polymerization, all the monomers in polymer must have structures that connect like key and lock. If we observe starch as an example of carbohydrates we’ll notice that it’s created of glucose molecules (monomer) lined up in exact order.
As the matter of lipids, they tend to form linear structures in combination with glycerol molecule called fatty acids. Depending on type of element that fatty acid forms connection with, lipid can be saturated (if the bond is between fatty acid and another carbon atom by single bond) or unsaturated (if there is at least on double carbon-carbon bond in chain).
Nucleic acids are polymers made of nucleotides (monomers). Each nucleotide consists of a 5-carbon sugar, a phosphate group and a nitrogenous base. Thus, there are two types of nucleic acids depending on sugar component. If the sugar component is ribose, nucleic acid would be RNA, or if there is deoxyriboze, formed nucleic acid would be DNA. If we take for an example DNA molecule, it has twisted chained structure thanks to the hydrogen bonds between phosphates. The nitrogenous bases are pointed inwards on the ladder where they form pairs with complementary nucleotides bounded by hydrogen bonds.
Proteins are polymers consisted of amino acids as monomers. Amino acids are compounds with amino group and carboxyl group on opposite ends, hydrogen atom and R group. R group is specific and it determines type of amino acid. Amino group of one amino acid connects with carboxyl group of another amino acid. Product of this reaction is peptide bond with releasing of water molecule.