NSEB — National Standard Examination in Biology

Which of the following bonds stabilizes the primary structure of proteins?

• AHydrogen bonds
• BPeptide bonds
• CDisulfide bonds
• DIonic bonds

A spherical cell has a radius of 2 micrometers. If its radius increases to 4 micrometers, how does its surface-area-to-volume ratio change?

• AIt doubles
• BIt remains unchanged
• CIt is halved
• DIt increases fourfold

In an enzyme-catalyzed reaction, what is the effect of a competitive inhibitor on the Michaelis constant (Km) and the maximum velocity (Vmax)?

• AKm increases and Vmax decreases
• BKm increases and Vmax remains unchanged
• CKm remains unchanged and Vmax decreases
• DKm decreases and Vmax remains unchanged

Which of the following cellular structures is responsible for the synthesis of lipids and the detoxification of drugs and poisons?

• ARough endoplasmic reticulum
• BSmooth endoplasmic reticulum
• CGolgi apparatus
• DLysosomes

During glycolysis, which enzyme catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate?

• AHexokinase
• BPhosphofructokinase-1
• CAldolase
• DPyruvate kinase

Under anaerobic conditions, yeast cells regenerate NAD+ by converting pyruvate into which of the following compounds?

• ALactate
• BEthanol and carbon dioxide
• CAcetyl-CoA
• DOxaloacetate

During the light reactions of photosynthesis, what is the primary function of photosystem II (PSII)?

• ATo generate NADPH
• BTo split water molecules and generate oxygen
• CTo synthesize ATP directly via photophosphorylation
• DTo fix carbon dioxide into sugars

Which of the following best describes the role of the Calvin cycle in C3 plants?

• AIt uses ATP and NADPH to convert carbon dioxide into G3P
• BIt splits water to release oxygen using solar energy
• CIt converts pyruvate into acetyl-CoA under aerobic conditions
• DIt generates ATP by moving protons down an electrochemical gradient

What is the thermodynamic significance of coupling endergonic reactions to ATP hydrolysis in biological systems?

• AIt increases the activation energy of the endergonic reaction
• BIt makes the overall free energy change (delta G) of the coupled reaction negative
• CIt prevents the cells from reaching thermal equilibrium
• DIt decreases the rate of the coupled reaction to maintain stability

Which of the following organelles contains its own DNA and ribosomally translates some of its own proteins?

• AGolgi apparatus
• BLysosome
• CMitochondrion
• DPeroxisome

How do C4 plants minimize photorespiration compared to C3 plants?

• ABy keeping their stomata completely closed during the day
• BBy physically separating carbon fixation and the Calvin cycle in different cells
• CBy using Rubisco to fix carbon dioxide at night
• DBy lacking the light-dependent reactions of photosynthesis

Which of the following occurs during prophase I of meiosis but not during prophase of mitosis?

• ACondensation of chromosomes
• BFormation of the spindle apparatus
• CSynapsis of homologous chromosomes
• DBreakdown of the nuclear envelope

Which of the following lipids is a major structural component of animal cell membranes and regulates membrane fluidity?

• ATriacylglycerol
• BCholesterol
• CStarch
• DGlycogen

In a mitochondrial electron transport chain, how many protons are pumped into the intermembrane space per pair of electrons transferred from NADH to oxygen?

• A4 protons
• B6 protons
• C10 protons
• D12 protons

Under physiological conditions, the reaction A -> B has a delta G of +15 kJ/mol. How can the cell drive this reaction forward?

• ABy increasing the temperature of the cell
• BBy coupling it to the hydrolysis of ATP (delta G = -30.5 kJ/mol)
• CBy using an enzyme to change the equilibrium constant
• DBy decreasing the concentration of reactant A

Which of the following processes occurs entirely within the cytosol of a eukaryotic cell?

• AKrebs cycle
• BOxidative phosphorylation
• CGlycolysis
• DPyruvate decarboxylation

What is the primary role of the signal recognition particle (SRP) during protein synthesis?

• ATo target ribosomes translating proteins with a signal peptide to the endoplasmic reticul…
• BTo cleave the signal peptide once the protein enters the lumen
• CTo assist in the folding of nascent polypeptide chains in the cytoplasm
• DTo degrade misfolded proteins in the proteasome

Which of the following occurs during the light-independent reactions (Calvin cycle) of photosynthesis?

• AWater is oxidized to oxygen gas
• BCarbon dioxide is fixed by Rubisco
• CProtons are pumped into the thylakoid space
• DChlorophyll molecules absorb photons

How does a non-competitive inhibitor affect the Km and Vmax of an enzyme-catalyzed reaction?

• AKm increases and Vmax decreases
• BKm remains unchanged and Vmax decreases
• CKm decreases and Vmax remains unchanged
• DKm and Vmax both decrease

Which of the following complexes in the mitochondrial inner membrane does NOT pump protons across the membrane?

• AComplex I (NADH dehydrogenase)
• BComplex II (Succinate dehydrogenase)
• CComplex III (Cytochrome bc1 complex)
• DComplex IV (Cytochrome c oxidase)

Which of the following plant tissues is responsible for the transport of water and dissolved minerals from the roots to the leaves?

• APhloem
• BXylem
• CParenchyma
• DCollenchyma

What is the primary mechanism described by the cohesion-tension theory for water transport in plants?

• AActive transport of water by root cells
• BCapillary action in narrow xylem vessels
• CTranspiration pulling water molecules held together by hydrogen bonds
• DRoot pressure forcing water upward against gravity

Which of the following plant hormones is responsible for promoting fruit ripening and leaf abscission?

• AAuxin
• BGibberellin
• CCytokinin
• DEthylene

In a root tip, where does the majority of cell division take place?

• AZone of elongation
• BZone of maturation
• CMeristematic zone
• DRoot cap

Which of the following occurs during stomatal opening?

• AK+ ions exit the guard cells, followed by water loss
• BK+ ions actively enter the guard cells, increasing turgor pressure
• CAbscisic acid (ABA) concentration in the guard cells increases
• DThe water potential of the guard cells increases relative to surrounding cells

According to the pressure-flow hypothesis, what drives the translocation of sugars in the phloem?

• AGravity pulling dense sap downward
• BA hydrostatic pressure gradient generated by osmotic water movement
• CActive transport of sugars by tracheids
• DTranspiration pull from the leaves

Which of the following is a primary physiological role of Gibberellins in plants?

• AMaintaining seed dormancy
• BInducing shoot elongation by stimulating cell division and elongation
• CPromoting lateral root growth while inhibiting primary root growth
• DPromoting stomatal closure during drought

What is the function of the Casparian strip in the endodermis of plant roots?

• ATo increase the surface area for water absorption
• BTo prevent water and solutes from entering the vascular cylinder via the apoplast
• CTo transport sugars from the phloem to the cortex cells
• DTo protect the root meristem from abrasion

In photoperiodism, what is the active light-receptor pigment that monitors photoperiod?

• AChlorophyll a
• BCarotenoids
• CPhytochrome
• DPlastocyanin

How does polar transport of auxin occur in plant stems?

• AUnidirectionally downward, mediated by PIN proteins located at the basal ends of cells
• BBidirectionally via xylem vessels
• CUnidirectionally upward via phloem companion cells
• DBy simple diffusion through the cuticle

Which of the following elements is a macronutrient in plants and is a central constituent of the chlorophyll molecule?

• AIron
• BMagnesium
• CBoron
• DManganese

What is the biological function of the endosperm in angiosperm seeds?

• ATo protect the embryo from physical shock
• BTo provide nutritive support to the developing embryo
• CTo absorb carbon dioxide for early photosynthesis
• DTo anchor the seed in the soil

Which of the following statements about C4 photosynthesis is correct?

• AIt requires more ATP per fixed glucose than C3 photosynthesis
• BIt uses Rubisco for the initial fixation of carbon dioxide in mesophyll cells
• CIt is favored in cool, wet environments
• DThe first stable product of carbon fixation is a 3-carbon phosphoglycerate

A scientist treats a dwarf plant with a hormone, and the plant grows to a normal height. Which hormone was most likely applied?

• AAbscisic acid
• BGibberellin
• CCytokinin
• DEthylene

Under what condition does the phenomenon of cavitation typically occur in xylem vessels?

• AHigh humidity and low transpiration rates
• BSevere water stress leading to high tension inside xylem vessels
• CExcessive active transport of minerals in the roots
• DExtremely alkaline soil conditions

Which of the following digestive enzymes is secreted in its inactive zymogen form to protect the secretory cells?

• AAmylase
• BPepsinogen
• CLipase
• DMaltase

During mammalian ventilation, which muscles contract to facilitate quiet, resting inhalation?

• AInternal intercostals and abdominal muscles
• BDiaphragm and external intercostals
• CDiaphragm and abdominal muscles
• DInternal intercostals and scalene muscles

Which portion of the nephron is impermeable to water but highly permeable to sodium and chloride ions?

• AProximal convoluted tubule
• BDescending limb of the loop of Henle
• CAscending limb of the loop of Henle
• DCollecting duct

What is the primary function of the sinoatrial (SA) node in the mammalian heart?

• ATo delay the electrical signal before it enters the ventricles
• BTo generate the spontaneous action potentials that establish heart rate
• CTo conduct electrical signals directly to the Purkinje fibers
• DTo prevent backflow of blood into the atria

Which of the following hormones is secreted by the posterior pituitary gland?

• AGrowth hormone (GH)
• BThyroid-stimulating hormone (TSH)
• CAntidiuretic hormone (ADH)
• DAdrenocorticotropic hormone (ACTH)

How does myelin increase the speed of action potential propagation along an axon?

• ABy increasing the diameter of the axon
• BBy allowing ions to flow continuously across the entire axonal membrane
• CBy forcing the action potential to jump between nodes of Ranvier
• DBy decreasing the resting membrane potential of the neuron

Which of the following parameters decreases during a shift to the right of the oxygen-hemoglobin dissociation curve?

• ATemperature
• BPartial pressure of carbon dioxide (PCO2)
• CHemoglobin's affinity for oxygen
• DConcentration of H+ ions (acidity)

Which cell type in the gastric glands is responsible for secreting hydrochloric acid (HCl)?

• AChief cells
• BParietal cells
• CMucous neck cells
• DG cells

In the sliding filament model of muscle contraction, which step requires the hydrolysis of ATP?

• ABinding of calcium to troponin
• BRe-cocking of the myosin head into the high-energy state
• CDetachment of the myosin head from the actin filament
• DBinding of the myosin head to the actin active site

Which hormone is released in response to low blood calcium levels and stimulates osteoclasts to resorb bone?

• ACalcitonin
• BThyroxine
• CParathyroid hormone (PTH)
• DAldosterone

What is the primary physiological function of the countercurrent multiplier system in the loop of Henle?

• ATo actively pump water out of the collecting duct
• BTo establish a concentration gradient in the renal medullary interstitium
• CTo excrete excess potassium ions from the blood
• DTo maintain a constant blood pressure within the glomerulus

Which of the following occurs immediately after the depolarization phase of a neuronal action potential?

• ASodium channels open and potassium channels close
• BSodium channels become inactivated and voltage-gated potassium channels open
• CThe sodium-potassium pump stops functioning
• DCalcium ions rush into the axon terminal