HESI A2 Elsevier (HESI): HESI Admission Assessment - Set 3 - Part 1

Correct Answer: Making an observation

Observation is the opening step of the scientific method, in which a scientist notices a phenomenon worth investigating. Every later step, including hypothesis, prediction, and experiment, depends on having something to observe first. Option a is incorrect because A hypothesis is a tentative testable explanation that comes only after a researcher has noticed a pattern or phenomenon worth explaining. It is therefore not the first step of the scientific method. Option b is incorrect because Experimental design comes after a hypothesis and a clear prediction have been written. Without an initial observation and resulting question, there would be nothing for an experiment to test in the first place. Option d is incorrect because Data analysis happens near the end of the process, after an experiment has been run and measurements collected. It cannot occur before observation because there would be no data yet to analyze at all.

Correct Answer: Definite geometric shape

Living organisms vary widely in shape, and many have no fixed geometric form at all. A definite geometric shape is a property of crystals and minerals, not a defining characteristic shared by all living things. Option b is incorrect because Response to stimuli is a required characteristic of life, because all organisms must detect and react to changes in their environment in order to survive. This applies from bacteria to humans alike. Option c is incorrect because Reproduction is a defining characteristic of life because every species must produce new individuals to continue. It can be sexual or asexual, but some form of reproduction occurs in all living organisms. Option d is incorrect because Homeostasis is required of all living organisms, since survival depends on maintaining stable internal conditions such as body temperature, pH levels, and ion balance despite changing external conditions in the surrounding environment.

Correct Answer: Tissue

A tissue is a group of similar cells working together to perform a shared function. The hierarchy goes cell, then tissue, then organ, so tissue is the level found immediately above the cell. Option a is incorrect because An organ is a structure made of two or more tissue types working together. It sits two levels above the cell, separated from the cell level by the tissue level itself. Option b is incorrect because An organelle is a subcellular structure such as the nucleus or mitochondrion. It is a level smaller than the cell, not larger, so it cannot be the level immediately above the cell in the hierarchy. Option c is incorrect because An organism is a complete living individual, several levels above the cell. Between cell and organism are tissue, organ, and organ system, so the organism cannot sit immediately above the cell on the ladder.

Correct Answer: Domain, Kingdom, Phylum, Class, Order, Family

Domain is the broadest rank, followed by kingdom, phylum, class, order, and family. The mnemonic Dear King Philip Came Over For Good Soup captures this exact order from broadest to most specific clearly. Option a is incorrect because Domain is broader than kingdom, so kingdom cannot come first in the list. The correct order begins with domain at the top and kingdom directly below it before continuing to phylum and the lower ranks. Option c is incorrect because Class does not come before phylum in the standard hierarchy. Phylum is broader than class, so listing class before phylum reverses an important pair within the lower portion of the taxonomic ranking system. Option d is incorrect because Domain is the broadest rank and must come first, not third. Listing kingdom before domain and inserting domain after phylum reverses the proper order within the upper portion of the taxonomic hierarchy.

Correct Answer: Homo sapiens

In binomial nomenclature the genus is capitalized and the species is lowercase, with both italicized or underlined. Homo sapiens follows this rule exactly and is the standard scientific name for modern humans worldwide. Option a is incorrect because Binomial nomenclature requires the genus to be capitalized, but here the genus name homo is in lowercase. The species name should also be lowercase, so this format gets both capitalization rules wrong at once. Option b is incorrect because The genus is capitalized correctly, but the species name should always be written in lowercase. Capitalizing the species name violates the standard formatting rules for binomial nomenclature in scientific writing today. Option d is incorrect because Writing the entire name in uppercase letters is not standard formatting. Only the first letter of the genus is capitalized, and the species name should remain in lowercase to follow proper binomial nomenclature in writing.

Correct Answer: Polar covalent

Within a water molecule, oxygen and hydrogen share electrons but oxygen attracts them more strongly. This unequal sharing creates a polar covalent bond, with partial negative charge on oxygen and partial positive charge on hydrogen. Option b is incorrect because A nonpolar covalent bond involves equal sharing of electrons between atoms of similar electronegativity. Oxygen is much more electronegative than hydrogen, so the sharing is unequal and the bond cannot be nonpolar covalent. Option c is incorrect because An ionic bond forms when electrons are completely transferred from one atom to another, creating ions. In water, electrons are shared rather than transferred, so the bond between oxygen and hydrogen cannot be ionic. Option d is incorrect because Hydrogen bonds are weak attractions that form between separate water molecules, not within a single water molecule. The strong bonds inside one water molecule between oxygen and hydrogen are covalent, not hydrogen bonds.

Correct Answer: Cohesion

Cohesion is the attraction of water molecules to other water molecules through hydrogen bonding. On a waxed surface, water cannot adhere to the wax, so cohesion pulls the molecules together into rounded beads on top. Option a is incorrect because Adhesion is the attraction of water molecules to a different substance. On a waxed surface water molecules are repelled by the wax, so adhesion is weak and cannot explain why water pulls itself. Option b is incorrect because High specific heat refers to the large amount of energy required to change the temperature of water. It explains temperature stability in oceans and bodies, not why water gathers into beads on a waxy surface. Option c is incorrect because The universal solvent property describes water dissolving many polar and ionic substances. It applies to mixing and dissolving, not to surface behavior, and does not explain why water forms tight droplets on wax.

Correct Answer: High specific heat

Water has a high specific heat, meaning it takes a large amount of energy to raise its temperature. This allows water to absorb heat without rapid temperature change, helping organisms and oceans stay stable. Option a is incorrect because Ice floats because solid water is less dense than liquid water, but this property does not relate to temperature regulation. It insulates aquatic life under ice, but it does not moderate temperature directly. Option c is incorrect because Water actually has high surface tension because of strong hydrogen bonding among its molecules, not low surface tension. Furthermore, surface tension affects the water surface, not its ability to moderate internal temperature in cells. Option d is incorrect because Water is a polar molecule because of unequal electron sharing in its covalent bonds. Polarity is what gives water its hydrogen bonding and high specific heat, so describing water as nonpolar is simply incorrect.

Correct Answer: Cohesion and adhesion together

Capillary action depends on adhesion of water to the tube walls and cohesion holding water molecules together. The two work as a team, pulling water up narrow plant vessels and similar small spaces. Option a is incorrect because Cohesion alone keeps water molecules joined to each other but does not pull water upward against gravity. Without adhesion to the inner walls of the tube, the water column could not climb upward. Option b is incorrect because Surface tension is a result of cohesion at the water surface but does not by itself drive movement up a tube. Capillary action requires both adhesion to the tube walls and cohesion among water molecules. Option d is incorrect because Hydrolysis is a chemical reaction in which water breaks bonds in larger molecules. It has nothing to do with the upward physical movement of water through plant stems and small tubes within plant tissues.

Correct Answer: Its polarity dissolves many polar substances

Water molecules are polar, with partial positive and partial negative ends. These charged regions surround and pull apart ionic and polar solutes, allowing water to dissolve a wide range of substances within cells. Option b is incorrect because Water actually has a relatively high boiling point compared with other small molecules of similar mass, due to extensive hydrogen bonding. Boiling point also is not the reason water dissolves so many different substances overall. Option c is incorrect because Water is polar, not nonpolar, and does not dissolve nonpolar substances like fats and oils well. Nonpolar substances mix poorly with water, which is why oil and water clearly separate in a glass into layers. Option d is incorrect because Water has no permanent net charge. Although its molecules have partial charges due to polarity, the molecule overall is electrically neutral, so a net charge cannot explain its solvent properties at all.

Correct Answer: Amino acid

Amino acids are the monomers of proteins. There are 20 standard amino acids, and they link together by peptide bonds to form polypeptide chains that fold into functional protein structures within the cell. Option a is incorrect because Nucleotides are the monomers of nucleic acids such as DNA and RNA. Each nucleotide contains a sugar, phosphate group, and nitrogenous base, which is the building block of genetic material rather than protein. Option b is incorrect because Monosaccharides are the monomers of carbohydrates, including glucose and fructose. They link together to form disaccharides and polysaccharides, but they are not the building blocks used to assemble proteins in living cells. Option c is incorrect because Fatty acids are components of certain lipids such as triglycerides and phospholipids. Lipids are not strictly polymers, and fatty acids are not the repeating units that form protein chains within living cells.

Correct Answer: Nucleic acid

Nucleic acids, including DNA and RNA, store and transmit genetic information. The sequence of nitrogenous bases along these molecules encodes instructions for building proteins and directing nearly all cellular activities daily. Option a is incorrect because Carbohydrates serve mainly as a quick energy source and as structural components such as cellulose. They are not used by cells to store inherited genetic instructions for building proteins or running cellular processes within tissues. Option c is incorrect because Proteins perform a huge range of jobs, such as catalyzing reactions, providing structure, and signaling between cells. However, the genetic blueprint that codes for proteins is stored in nucleic acids, not in proteins. Option d is incorrect because Lipids form membranes, store long-term energy, and serve as steroid hormones. They do not contain a sequence of bases that can encode hereditary information passed from one generation of cells to the next.

Correct Answer: Short-term energy and structural support

Carbohydrates such as glucose provide quick energy, while glycogen stores energy in animals and starch in plants. They also form structural components like cellulose in plant cell walls and chitin in fungi and arthropods. Option b is incorrect because Storing genetic information is the role of nucleic acids, particularly DNA. Carbohydrates do not encode hereditary instructions, although some sugar units appear within the backbone of DNA and RNA molecules during replication. Option c is incorrect because Catalyzing chemical reactions is the role of enzymes, which are almost always proteins. Carbohydrates do not function as biological catalysts and lack the precise three-dimensional active sites needed for catalysis of reactions. Option d is incorrect because Cell membranes are formed mainly by phospholipids and proteins. Although some carbohydrates attach to membrane proteins as glycoproteins, carbohydrates do not form the basic structural framework of the membrane itself today.

Correct Answer: Glycogen

Glycogen is a branched polymer of glucose units, which makes it a carbohydrate, not a lipid. It is the main form of carbohydrate energy storage in animal cells, especially in the liver and muscle tissue. Option a is incorrect because A triglyceride is a lipid composed of glycerol attached to three fatty acid chains. It is the main form of stored fat in animals and serves as a long-term energy reserve in adipose tissue. Option b is incorrect because A phospholipid is a lipid containing two fatty acid tails and a phosphate-containing head. Phospholipids form the bilayer that makes up the basic structure of all biological membranes inside cells of living organisms. Option d is incorrect because Cholesterol is a steroid lipid that is embedded in animal cell membranes and serves as a precursor for steroid hormones. Despite its ring structure, it is grouped with the lipids due to hydrophobicity.

Correct Answer: Peptide bond

A peptide bond is the covalent bond formed between the carboxyl group of one amino acid and the next amino group. Many peptide bonds in a row create the polypeptide chain of proteins. Option a is incorrect because Glycosidic bonds link sugar units together in carbohydrates, such as the bond between two glucose molecules in maltose. They do not appear between amino acids and are not used to build protein chains. Option b is incorrect because Phosphodiester bonds connect adjacent nucleotides along the backbone of DNA and RNA. They join the sugar of one nucleotide to the phosphate of the next, but they do not connect amino acids. Option c is incorrect because Ester bonds form between fatty acids and glycerol in triglycerides and other lipids. They do not connect the amino group and carboxyl group of two amino acids during protein synthesis on the ribosome.

Correct Answer: Building large molecules from smaller ones

Anabolism refers to building larger, more complex molecules from smaller ones, and it requires an input of energy. Examples include making proteins from amino acids and creating glycogen from glucose units in the cell. Option a is incorrect because Breaking down large molecules into smaller ones describes catabolism, not anabolism. Catabolic reactions release energy and include processes such as digestion of food and cellular respiration of glucose in the body. Option c is incorrect because Releasing heat without doing work is not the definition of anabolism. Anabolism is specifically a constructive process that uses energy to build complex molecules, regardless of any heat released as a side product. Option d is incorrect because Transporting molecules across membranes is membrane transport, which can be active or passive. It is a separate process from anabolism, which describes the chemical building of molecules within the cell during metabolism.

Correct Answer: It lowers the activation energy

An enzyme is a biological catalyst that lowers the activation energy required to start a reaction. By lowering this energy barrier, the enzyme greatly speeds up the rate of the reaction without being consumed itself. Option a is incorrect because Enzymes lower, not raise, activation energy. Increasing activation energy would slow down the reaction, which is the opposite of how enzymes function as biological catalysts in living systems and inside human cells. Option b is incorrect because Enzymes are not permanently changed by the reactions they catalyze. After releasing their products, enzymes return to their original shape and can be reused many times to catalyze additional reactions in the cell. Option d is incorrect because Enzymes do not supply energy for reactions. They lower the energy barrier so that existing energy in the system is more likely to drive the reaction forward, but they do not provide the energy themselves.

Correct Answer: The region where substrate binds and reacts

The active site is a specific region of an enzyme with a shape that fits a particular substrate. When substrate binds at this site, the enzyme catalyzes the reaction by lowering the activation energy. Option b is incorrect because Enzymes do not contain a region that supplies energy for reactions. They reduce the activation energy needed but do not produce energy. Energy for reactions usually comes from molecules such as ATP within the cell. Option c is incorrect because An enzyme is not normally broken down at any specific region during catalysis. Enzymes are reusable catalysts, so they retain their structure after each reaction and are not destroyed by the substrate during the reaction. Option d is incorrect because DNA copying takes place inside the nucleus and uses DNA polymerase enzymes, but DNA replication is not a function of the active site of every enzyme. Most enzymes catalyze reactions unrelated to DNA copying directly.

Correct Answer: An energy carrier used in reactions

ATP is a nucleotide that serves as the main energy currency of cells. When its terminal phosphate bond is broken, energy is released that drives many cellular reactions, from muscle contraction to active transport. Option a is incorrect because ATP is structurally similar to a nucleotide, but it does not store genetic information. Genetic information is stored in DNA, which is composed of long strands of nucleotides linked into a double helix. Option b is incorrect because A polysaccharide such as glycogen is a long chain of sugars used for long-term energy storage. ATP is a small molecule that provides immediate energy to power individual cellular reactions, not stored energy at all. Option c is incorrect because ATP is not a lipid and is not part of the cell membrane. Cell membranes are made primarily of phospholipids and proteins, while ATP circulates within the cytoplasm and is consumed during metabolic reactions.

Correct Answer: Protein synthesis is anabolic

Protein synthesis links amino acids together to form polypeptide chains, which builds a complex molecule from simpler ones. Building reactions that require energy are classified as anabolic, so this pairing is correct in metabolism. Option a is incorrect because Photosynthesis builds glucose from carbon dioxide and water using light energy, so it is anabolic, not catabolic. Catabolic processes break complex molecules down, while anabolic processes assemble them from smaller building blocks. Option b is incorrect because Cellular respiration breaks down glucose to release energy as ATP, making it a catabolic process. Anabolic processes build molecules and require energy, which is the opposite of what respiration does inside the mitochondria of cells. Option d is incorrect because Digestion breaks down large food molecules such as starches and proteins into smaller subunits. Because complex molecules are broken into simpler ones, digestion is classified as catabolic rather than anabolic