BIOL 121 – Exam 1 | Fall 2026

What characteristics are common to all living organisms?

Living things are made of cells, use energy, maintain homeostasis, grow and develop, respond to their environment, reproduce, contain genetic information, and evolve as populations.

What is homeostasis?

The ability of an organism to maintain stable internal conditions even when the outside environment changes.

What is metabolism?

All of the chemical reactions that occur inside a living organism.

What is evolution?

Change in the inherited traits of a population over many generations.

What is a cell?

The basic structural and functional unit of life.

What is an atom?

The smallest unit of an element that still has the properties of that element.

What are the three main subatomic particles?

Protons, neutrons, and electrons.

What charge does a proton have?

Positive.

What charge does a neutron have?

No charge.

What charge does an electron have?

Negative.

Where are protons and neutrons located?

In the nucleus of an atom.

Where are electrons located?

In electron shells surrounding the nucleus.

What is an electron shell?

A region around the nucleus where electrons are found.

Why are valence electrons important?

They are the outermost electrons and determine how an atom bonds with other atoms.

What is the octet rule?

Atoms tend to become stable when they have 8 electrons in their outer electron shell.

How many electrons can the first electron shell hold?

2 electrons.

How many electrons can the second electron shell generally hold in biological atoms?

8 electrons.

What is a chemical bond?

An attraction that holds atoms together.

What is a covalent bond?

A strong bond in which atoms share electrons.

What is a nonpolar covalent bond?

A covalent bond where electrons are shared approximately equally between atoms.

What is a polar covalent bond?

A covalent bond where electrons are shared unequally between atoms.

What is an ionic bond?

An attraction between oppositely charged ions after electrons have been transferred from one atom to another.

What is a hydrogen bond?

A weak attraction between a slightly positive hydrogen and a slightly negative atom in another molecule or another part of a molecule.

Which biological bond is generally the strongest?

Covalent bonds.

How do hydrogen bonds compare with covalent bonds?

Hydrogen bonds are much weaker individually than covalent bonds.

What is an ion?

An atom or molecule that has gained or lost electrons and has an electrical charge.

What is a cation?

A positively charged ion.

What is an anion?

A negatively charged ion.

Where are covalent bonds found in cells?

Within biological molecules such as proteins, carbohydrates, lipids, and nucleic acids.

Where are hydrogen bonds commonly found in cells?

Between water molecules and within molecules such as proteins and DNA.

What is a polar molecule?

A molecule with an uneven distribution of electrical charge.

Why is water polar?

Oxygen pulls shared electrons more strongly than hydrogen, giving oxygen a partial negative charge and hydrogen partial positive charges.

Why can water form hydrogen bonds?

The partially positive hydrogen of one water molecule is attracted to the partially negative oxygen of another.

Why is water important for life?

It is an excellent solvent, participates in chemical reactions, helps control temperature, allows transport of substances, and supports biological structures.

What does it mean that water is a good solvent?

Many charged and polar substances can dissolve in water.

What is cohesion?

Attraction between molecules of the same substance, such as water molecules sticking to each other.

What is adhesion?

Attraction between molecules of different substances, such as water sticking to glass or plant tissue.

What causes water's surface tension?

Hydrogen bonds between water molecules.

Why does water have a high specific heat?

Hydrogen bonds allow water to absorb a lot of heat before its temperature changes greatly.

How does water's high specific heat help life?

It helps organisms and environments maintain stable temperatures.

Why does sweating cool the body?

High-energy water molecules evaporate from the skin and carry heat away.

Why does ice float?

Solid water forms a hydrogen-bonded structure that spaces molecules farther apart, making ice less dense than liquid water.

Why is floating ice important for aquatic life?

Ice forms an insulating layer on top of water instead of freezing lakes from the bottom upward.

What is carbon's special role in biology?

Carbon can form four covalent bonds, allowing it to create many different stable and complex molecules.

Why can carbon make chains and rings?

Carbon atoms can form strong covalent bonds with other carbon atoms.

Why is carbon central to biological molecules?

Its four bonding sites allow great structural diversity.

Why is silicon not used as widely as carbon in living organisms?

Silicon does not form the same variety of stable, flexible molecules under biological conditions as carbon.

Why is aluminum not a major backbone element of life?

It does not form stable complex covalent chains like carbon and often exists as charged ions or minerals.

What is an isotope?

Atoms of the same element with the same number of protons but different numbers of neutrons.

Do isotopes usually behave differently in ordinary chemical reactions?

Usually they behave similarly because they have the same number of electrons, although some isotopes may differ slightly in reaction rates or stability.

What is a radioactive isotope?

An unstable isotope that breaks down and releases radiation.

What are the four major groups of biological macromolecules?

Carbohydrates, lipids, proteins, and nucleic acids.

What is a monomer?

A small building-block molecule that can be joined with others.

What is a polymer?

A large molecule made from many repeating monomers.

What is dehydration synthesis or condensation?

A reaction that joins smaller molecules together while removing water.

What is hydrolysis?

A reaction that breaks a large molecule apart by adding water.

How are biological polymers usually formed?

Monomers are joined together through dehydration reactions.

How are biological polymers usually broken apart?

Through hydrolysis reactions.

What are carbohydrates mainly made of?

Carbon, hydrogen, and oxygen.

What is the basic monomer of a carbohydrate?

A monosaccharide, or simple sugar.

What is an example of a monosaccharide?

Glucose.

How are monosaccharides joined together?

By dehydration reactions that form glycosidic bonds.

What is a disaccharide?

A carbohydrate made from two monosaccharides joined together.

What is a polysaccharide?

A large carbohydrate made from many monosaccharides.

What is starch?

A glucose-storage polysaccharide found mainly in plants.

What is glycogen?

A highly branched glucose-storage polysaccharide found mainly in animals.

Where is glycogen stored in humans?

Mostly in the liver and muscles.

What is cellulose?

A structural polysaccharide found in plant cell walls.

What is the function of cellulose?

It provides strength and support to plant cell walls.

Why can't humans digest cellulose?

Humans lack the enzyme needed to break the beta glycosidic bonds in cellulose.

What happens to cellulose when humans eat it?

It acts mainly as dietary fiber.

Why are carbohydrates necessary for life?

They provide energy, store energy, and can provide structural support.

What is the main immediate energy source for many cells?

Glucose.

What are lipids?

A diverse group of mostly nonpolar, hydrophobic biological molecules.

Are lipids true polymers?

No. Most lipids are not made from long repeating chains of identical monomers.

What does hydrophobic mean?

Does not mix or interact well with water.

What is the basic structure of a triglyceride?

One glycerol molecule attached to three fatty acids.

How is a triglyceride formed?

Glycerol and three fatty acids are joined through dehydration reactions.

What is a fatty acid?

A long hydrocarbon chain with a carboxyl group at one end.

What is a saturated fatty acid?

A fatty acid with no carbon-carbon double bonds.

What is an unsaturated fatty acid?

A fatty acid with one or more carbon-carbon double bonds.

What is a phospholipid?

A lipid made of glycerol, two fatty acid tails, and a phosphate-containing polar head.

Which part of a phospholipid is hydrophilic?

The phosphate-containing head.

Which part of a phospholipid is hydrophobic?

The fatty acid tails.

Why do phospholipids spontaneously form membranes in water?

The hydrophilic heads face the water while the hydrophobic tails group together away from the water.

What is a phospholipid bilayer?

A double layer of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward.

Why are phospholipids important for life?

They form the basic structure of cell membranes.

What are steroids?

Lipids made of four connected carbon rings.

Why are steroids considered lipids?

They are mostly hydrophobic and do not dissolve well in water.

What is cholesterol?

A steroid that is an important component of animal cell membranes and a starting material for some hormones.

What are examples of steroid hormones?

Testosterone, estrogen, cortisol, and progesterone.

Why are lipids necessary for life?

They store energy, form cell membranes, insulate and protect the body, and can act as hormones or signaling molecules.

What are proteins made of?

Amino acids.

What is the basic structure of an amino acid?

A central carbon attached to an amino group, a carboxyl group, a hydrogen, and a variable R group.

What part of an amino acid makes one amino acid different from another?

The R group or side chain.

What is a peptide bond?

A covalent bond joining the amino group of one amino acid to the carboxyl group of another.

How are peptide bonds formed?

Through dehydration reactions.

What is a polypeptide?

A chain of amino acids connected by peptide bonds.

What determines the primary structure of a protein?

The order or sequence of amino acids.

What are the four levels of protein structure?

Primary, secondary, tertiary, and quaternary.