USABO Latest Update 2025-2026 Exam 870
Questions with 100% Verified Correct Answers
Guaranteed A+
(Eastern) Hemlock - CORRECT ANSWER: Tsuga canadensis
~5 nm - CORRECT ANSWER: approximate thickness of the cell membrane (include
label)
1 nm - CORRECT ANSWER: size of a molecule (include label)
1 µm - CORRECT ANSWER: size of bacteria (include label)
10-100 nm - CORRECT ANSWER: size of a virus (include label)
10-100 µm - CORRECT ANSWER: size of eukaryotic cells (include label)
3 useful functions of TCA cycle - CORRECT ANSWER: 1. Uses glucose atoms to form
reduced coenzymes. In the last stage of glucose oxidation (the electron transport chain)
these H atoms finally make energy available as ATP, through the process of oxidative
phosphorylation.
2. It produces a molecule of ATP by substrate level phosphorylation (reaction T5). Since
the cycle turns twice for every glucose oxidised , the yield is 2 ATP's per glucose
molecule.
3. It produces carbon intermediates for biosynthesis. This is particularly relevant in
plants, where biosynthesis rather than energy production is the main role of the TCA
cycle.
Absorption - CORRECT ANSWER: Cells stake up small molecules (amino acids, simple
sugars, etc.) from the digestive compartment
3rd stage of food processing
,absorption spectrum - CORRECT ANSWER: The range of a pigment's ability to absorb
various wavelengths of light; also a graph of such a range.
acetyl CoA - CORRECT ANSWER: Acetyl coenzyme A; the entry compound for the citric
acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a
coenzyme.
acetyl CoA - CORRECT ANSWER: An intermediate compound formed during the
breakdown of glucose by adding a two-carbon fragment to a carrier molecule
Acetylcholine - CORRECT ANSWER: Common neurotransmitter in vertebrates and
invertebrates
acid - CORRECT ANSWER: a substance that increases the number of hydrogen ions in
a solution
Acid Chyme - CORRECT ANSWER: A nutrient-rich broth of swallowed food found in the
stomach
actin - CORRECT ANSWER: A globular protein that links into chains, two of which twist
helically about each other, forming microfilaments (actin filaments) in muscle and other
kinds of cells.
Action Potential - CORRECT ANSWER: Response to stimulus strong enough to cause
depolarization to reach the threshold
action spectrum - CORRECT ANSWER: A graph that profiles the relative effectiveness
of different wavelengths of radiation in driving a particular process.
activation energy - CORRECT ANSWER: The amount of energy that reactants must
absorb before a chemical reaction will start; also called free energy of activation.
,active site - CORRECT ANSWER: The specific portion of an enzyme that binds the
substrate by means of multiple weak interactions and that forms the pocket in which
catalysis occurs.
Active transport - CORRECT ANSWER: This form of transport is the movement of a
substance against its concentration gradient (from low to high concentration). In all
cells, this is usually concerned with accumulating high concentrations of molecules that
the cell needs, such as ions, glucose, and amino acids. If the process uses chemical
energy, such as from adenosine triphosphate (ATP), it is termed primary active
transport. Secondary active transport involves the use of an electrochemical gradient.
Active transport uses energy, unlike passive transport, which does not use any type of
energy. Active transport is a good example of a process for which cells require energy.
Examples of active transport include the uptake of glucose in the intestines in humans
and the uptake of mineral ions into root hair cells of plants.
active transport - CORRECT ANSWER: transport of molecules against a concentration
gradient with the aid of ATP
adaptive radiation - CORRECT ANSWER: Period of evolutionary change in which
groups of organisms form many new species whose adaptations allow them to fill
vacant ecological roles in their communities.
additions to population size happen because? - CORRECT ANSWER: reproduction,
immigration
Adenine - CORRECT ANSWER: Also known as A and Ade, this is a nucleobase (a
purine derivative) with a variety of roles in biochemistry including cellular respiration, in
the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors
nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), and
protein synthesis, as a chemical component of DNA and RNA.[2] The shape of adenine
is complementary to either thymine in DNA or uracil in RNA.
Adenine - CORRECT ANSWER: one of the four nitrogenous bases occurring in DNA
and RNA- matches with Thymine in DNA and Urasil in RNA
, Adenine Diphosphate - CORRECT ANSWER: Lower energy form of ATP, has only two
attached phosphate groups
adenosine triphosphate (ATP) - CORRECT ANSWER: An adenine-containing
nucleoside triphosphate that releases free energy when its phosphate bonds are
hydrolyzed. This energy is used to drive endergonic reactions in cells.
adenylyl cyclase - CORRECT ANSWER: An enzyme that converts ATP to cyclic AMP in
response to a signal.
Adherens Junctions - CORRECT ANSWER: These junctions function in the same way
as anchoring junctions, linking intercellular cytoskeletons using cadherin. Unlike the
anchoring junctions these junctions use the actin filaments not the intermediate
filaments to secure the cells.
adhesion - CORRECT ANSWER: attraction between molecules of different substances
aerobic respiration - CORRECT ANSWER: A catabolic pathway that consumes oxygen
(O2) and organic molecules, producing ATP. This is the most efficient catabolic pathway
and is carried out in most eukaryotic cells and many prokaryotic organisms.
Afferent Arteriole - CORRECT ANSWER: A branch of the renal artery that subdivides
into the capillaries of the glomerulus
Supplies nephrons with blood
age structure - CORRECT ANSWER: relative number of individuals in each stage
Alanine - CORRECT ANSWER: Alanine (abbreviated as Ala or A)[2] is an α-amino acid
with the chemical formula CH3CH(NH2)COOH. It can be synthesized from the pyruvate
intermediate of the TCA cycle. The L-isomer is one of the 22 proteinogenic amino acids,
i.e., the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is
classified as a nonpolar amino acid. L-Alanine is second only to leucine in rate of
occurrence, accounting for 7.8% of the primary structure in a sample of 1,150
proteins.D-Alanine occurs in bacterial cell walls and in some peptide antibiotics.
Questions with 100% Verified Correct Answers
Guaranteed A+
(Eastern) Hemlock - CORRECT ANSWER: Tsuga canadensis
~5 nm - CORRECT ANSWER: approximate thickness of the cell membrane (include
label)
1 nm - CORRECT ANSWER: size of a molecule (include label)
1 µm - CORRECT ANSWER: size of bacteria (include label)
10-100 nm - CORRECT ANSWER: size of a virus (include label)
10-100 µm - CORRECT ANSWER: size of eukaryotic cells (include label)
3 useful functions of TCA cycle - CORRECT ANSWER: 1. Uses glucose atoms to form
reduced coenzymes. In the last stage of glucose oxidation (the electron transport chain)
these H atoms finally make energy available as ATP, through the process of oxidative
phosphorylation.
2. It produces a molecule of ATP by substrate level phosphorylation (reaction T5). Since
the cycle turns twice for every glucose oxidised , the yield is 2 ATP's per glucose
molecule.
3. It produces carbon intermediates for biosynthesis. This is particularly relevant in
plants, where biosynthesis rather than energy production is the main role of the TCA
cycle.
Absorption - CORRECT ANSWER: Cells stake up small molecules (amino acids, simple
sugars, etc.) from the digestive compartment
3rd stage of food processing
,absorption spectrum - CORRECT ANSWER: The range of a pigment's ability to absorb
various wavelengths of light; also a graph of such a range.
acetyl CoA - CORRECT ANSWER: Acetyl coenzyme A; the entry compound for the citric
acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a
coenzyme.
acetyl CoA - CORRECT ANSWER: An intermediate compound formed during the
breakdown of glucose by adding a two-carbon fragment to a carrier molecule
Acetylcholine - CORRECT ANSWER: Common neurotransmitter in vertebrates and
invertebrates
acid - CORRECT ANSWER: a substance that increases the number of hydrogen ions in
a solution
Acid Chyme - CORRECT ANSWER: A nutrient-rich broth of swallowed food found in the
stomach
actin - CORRECT ANSWER: A globular protein that links into chains, two of which twist
helically about each other, forming microfilaments (actin filaments) in muscle and other
kinds of cells.
Action Potential - CORRECT ANSWER: Response to stimulus strong enough to cause
depolarization to reach the threshold
action spectrum - CORRECT ANSWER: A graph that profiles the relative effectiveness
of different wavelengths of radiation in driving a particular process.
activation energy - CORRECT ANSWER: The amount of energy that reactants must
absorb before a chemical reaction will start; also called free energy of activation.
,active site - CORRECT ANSWER: The specific portion of an enzyme that binds the
substrate by means of multiple weak interactions and that forms the pocket in which
catalysis occurs.
Active transport - CORRECT ANSWER: This form of transport is the movement of a
substance against its concentration gradient (from low to high concentration). In all
cells, this is usually concerned with accumulating high concentrations of molecules that
the cell needs, such as ions, glucose, and amino acids. If the process uses chemical
energy, such as from adenosine triphosphate (ATP), it is termed primary active
transport. Secondary active transport involves the use of an electrochemical gradient.
Active transport uses energy, unlike passive transport, which does not use any type of
energy. Active transport is a good example of a process for which cells require energy.
Examples of active transport include the uptake of glucose in the intestines in humans
and the uptake of mineral ions into root hair cells of plants.
active transport - CORRECT ANSWER: transport of molecules against a concentration
gradient with the aid of ATP
adaptive radiation - CORRECT ANSWER: Period of evolutionary change in which
groups of organisms form many new species whose adaptations allow them to fill
vacant ecological roles in their communities.
additions to population size happen because? - CORRECT ANSWER: reproduction,
immigration
Adenine - CORRECT ANSWER: Also known as A and Ade, this is a nucleobase (a
purine derivative) with a variety of roles in biochemistry including cellular respiration, in
the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors
nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), and
protein synthesis, as a chemical component of DNA and RNA.[2] The shape of adenine
is complementary to either thymine in DNA or uracil in RNA.
Adenine - CORRECT ANSWER: one of the four nitrogenous bases occurring in DNA
and RNA- matches with Thymine in DNA and Urasil in RNA
, Adenine Diphosphate - CORRECT ANSWER: Lower energy form of ATP, has only two
attached phosphate groups
adenosine triphosphate (ATP) - CORRECT ANSWER: An adenine-containing
nucleoside triphosphate that releases free energy when its phosphate bonds are
hydrolyzed. This energy is used to drive endergonic reactions in cells.
adenylyl cyclase - CORRECT ANSWER: An enzyme that converts ATP to cyclic AMP in
response to a signal.
Adherens Junctions - CORRECT ANSWER: These junctions function in the same way
as anchoring junctions, linking intercellular cytoskeletons using cadherin. Unlike the
anchoring junctions these junctions use the actin filaments not the intermediate
filaments to secure the cells.
adhesion - CORRECT ANSWER: attraction between molecules of different substances
aerobic respiration - CORRECT ANSWER: A catabolic pathway that consumes oxygen
(O2) and organic molecules, producing ATP. This is the most efficient catabolic pathway
and is carried out in most eukaryotic cells and many prokaryotic organisms.
Afferent Arteriole - CORRECT ANSWER: A branch of the renal artery that subdivides
into the capillaries of the glomerulus
Supplies nephrons with blood
age structure - CORRECT ANSWER: relative number of individuals in each stage
Alanine - CORRECT ANSWER: Alanine (abbreviated as Ala or A)[2] is an α-amino acid
with the chemical formula CH3CH(NH2)COOH. It can be synthesized from the pyruvate
intermediate of the TCA cycle. The L-isomer is one of the 22 proteinogenic amino acids,
i.e., the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is
classified as a nonpolar amino acid. L-Alanine is second only to leucine in rate of
occurrence, accounting for 7.8% of the primary structure in a sample of 1,150
proteins.D-Alanine occurs in bacterial cell walls and in some peptide antibiotics.
