Introductory Topics - Biology

Water is a very important molecule in order for life to take place. It is the solvent in which chemical reactions take place, as well as a reactant for certain reactions. Water's polarity also causes polar molecules to dissolve and nonpolar compounds to aggregate. As a result, nonpolar molecules are not dissolved in water.

Water is often called the universal solvent and is one of the most important compounds on Earth. The molecular structure of water promotes intermolecular hydrogen bonding, a very strong force between molecules. The result is known as cohesion, the phenomenon of water molecules "sticking" to one another. Cohesion leads to other water properties, such as high surface tension and capillary action, which are essential to supporting life. Hydrogen bonding is only possible in water molecules because of the polarity of the bond between oxygen and hydrogen; oxygen carries a partial negative charge, and hydrogen carries a partial positive charge. Water also have a very high specific heat, which means that it requires a lot of energy to raise the temperature of water. This promotes homeostasis and temperature stability in biological organisms.

In the liquid state, cohesion promotes stability, but in the gaseous state water molecules must separate from one another to move around. Essentially, cohesion must be overcome in order for water to boil. This leads to a high heat of vaporization, rather than a low heat of vaporization.

In the water cycle, there are abiotic and biotic factors that contribute to the recycling of water. The process by which non-living things return water to the atmosphere is called evaporation. Plants, on the other hand, intake water through their roots and release the water as vapor through tiny openings on leaves called stomata. This process is called transpiration.

Molecules that are hydrophobic or "water fearing" will have a hard time dissolving in an aqueous solution. Lipids, which are nonpolar molecules, would not be able to dissolve in water.

When water freezes, its density decreases (most substances do not exhibit this property). This means that ice will float on top of a lake, rather than sink to the bottom. Because the ice floats on top of a lake, it freezes from the top down rather than from the bottom up. The other answer choices are all properties of water, but they do not explain why lakes freeze from top down, and not from bottom up.

Hydrolysis is the reverse of a dehydration reaction; the bond between monomers is broken by the addition of a water molecule, with a hydrogen atom from water attaching to one monomer and the hydroxyl group attaching to the other.

Water is unique in many ways. Much of its versatility is due to hydrogen bonding and polarity. The electronegativity of the oxygen atom creates a slightly positive charge on the hydrogen atoms—water is polar. Water can share hydrogen bonds and form them with itself. Because of this it has a high boiling point and high heat capacity. It is a good solvent because the oxygen can surround positively charged molecules and the slight positive charge on the hydrogen atoms can surround negative charges.

The cohesive nature of water stems from the fact it forms hydrogen bonds with itself. This allows water molecules to pull on lower molecules as they all travel up the xylem. The adhesive nature comes from the polarity of the molecule, which can be attracted to the walls of the xylem.

Water actually has a high specific heat, higher than any other common substance. A high specific heat (defined as the amount of heat needed to raise one mass unit of substance by one unit of temperature, usually expressed in or ) means that water can absorb a large amount of heat without changing temperature. This makes it important for organisms in things like thermoregulation (think prespiration).

Peroxisomes are responsible for detoxification. They contain many enzymes that breakdown lipids and amino acids. Additionally, they breakdown toxins like alcohol in the cells of the liver.

The correct order of the level of organization of an individual is as follows: cells, tissue, organs, organ systems, and organism. In other words, tissues form organs. For example, in a human being the order in the musculatory system would be: muscle cell, muscle tissue, bicep muscle, musculatory system, and human being.

The R group is a side chain connected to the central carbon atom in an amino acid. The central carbon atom of an amino acid can bind to four other groups. In an amino acid, the central carbon will always bind to a carboxyl group, and amine group, and a hydrogen atom. The fourth bond, however, will be different for each amino acid, linking the central carbon to the R group.

Waxes provide skin with a waterproof coating. Waxes are made out of fats.

Hemoglobin is a protein responsible for transporting oxygen. DNA polymerase repairs DNA molecules. Amylase is the protein that helps convert starch to glucose.

Proteins are synthesized through dehydration synthesis reactions, which is the removal of water between two amino acids. In this case, two hydrogen atoms are removed from the amine group and one oxygen is removed from the carboxyl group, forming a peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other amino acid.

The sequence of amino acids is called a protein's primary structure. Each protein has a unique sequence of amino acids. A difference of just one amino acid in a chain of hundreds can be deadly to the organism. For example, mutation leading to a single amino acid change is responsible for sickle cell anemia.

A helix is formed when Hydrogen bonds occur between the amino group in one peptide bond and the carboxyl group of another in the same polypeptide chain.

The cell theory has three basic parts: all living things are made of cells, the cell is the smallest unit of life, and all cells come from preexisting cells. Prokaryotic cells are indeed cells and they do not contradict any tenets of the cell theory. However, they do not contain nuclei; rather, their genetic material is contained in the cytoplasm.

The pH of a solution is defined as the the concentration of H+ ions in the solution. The pH of a solution declines as H+ concentration increases. On the pH scale, ranging from 0 to 14, 7 is neutral. Substances below 7 are more acidic, 0 being the most acidic. Substances above 7 are more basic, 14 being the most basic.

“Composed of plutonium” is not a characteristic of a living organism. The other three choices are characteristics of living organisms. Organisms use energy in their metabolic processes. Organisms reproduce either asexually or sexually to make offspring for the next generation. Organisms from the simplest prokaryote to the human species contain DNA—the universal genetic code.

All amino acids contain carbon, hydrogen, oxygen, and nitrogen. These elements create a carboxylic acid group and an amine group, which can fuse to form a peptide bond. Peptide bonds hold amino acids together and generate the primary structure of the protein.

Cysteine, a specific amino acid, also contains sulfur. Thus, the correct answer is that carbon, oxygen, hydrogen, nitrogen, and sulfur can all be found in amino acids.

Phosphorus is never found in amino acids, but plays an important role in the structure of nucleic acids, such as DNA, and in the modification and activation of proteins.

All life forms must be able to uptake or produce energy to survive (metabolism), grow, and reproduce to propagate the species. While having a safe place to live is an ideal for most species, it is not a requirement of life.

These criteria can be tested by thinking of a single cell. A single cell requires energy, and can metabolize it via glycolysis (even in an anaerobic environment). A cell can grow, and does so during the G1 phase of the cell cycle. A cell is also capable of reproducing via mitosis. A single cells does not, however, require shelter; some cells live in highly extreme environments.