RISE Science — Biology

In a Utah forest ecosystem, lodgepole pine trees photosynthesize to convert radiant solar energy into chemical energy. Which balanced chemical equation accurately represents the primary inputs and products of photosynthesis?

• A6 CO2 + 6 H2O + light energy -> C6H12O6 + 6 O2
• BC6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP
• C6 CO2 + 6 O2 + light energy -> C6H12O6 + 6 H2O
• DC6H12O6 + 6 H2O -> 6 CO2 + 6 O2 + light energy

During the light-dependent reactions in a plant thylakoid membrane, water molecules are split (photolysis). What are the immediate products of this water-splitting event?

• AOxygen gas, hydrogen ions (protons), and electrons
• BCarbon dioxide gas, glucose, and ATP
• CNADPH, G3P, and ribulose bisphosphate (RuBP)
• DLactic acid, NAD+, and pyruvate

The Calvin cycle takes place in the stroma of chloroplasts. Which enzyme catalyzes the initial carbon fixation step by combining CO2 with a 5-carbon sugar?

• ARibulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO)
• BATP synthase
• CDNA polymerase III
• DPhosphofructokinase

A bioenergetics researcher measures gas exchange in plant tissue in the dark. Which process explains why the tissue consumes O2 and releases CO2?

• AAerobic cellular respiration
• BLight-dependent photosynthetic reactions
• CPhotophosphorylation
• DNitrogen fixation

Glycolysis is the initial pathway of cellular respiration occurring in the cytoplasm. What is the net yield of ATP and electron carriers per molecule of glucose oxidized in glycolysis?

• A2 ATP and 2 NADH
• B32 ATP and 6 FADH2
• C4 ATP and 2 FADH2
• D0 ATP and 4 NADH

Before entering the Krebs cycle, pyruvate produced in glycolysis is transported into the mitochondrial matrix. What chemical transformation converts pyruvate into acetyl-CoA?

• ADecarboxylation releasing CO2 and reduction of NAD+ to NADH
• BPhosphorylation consuming 2 ATP molecules
• CCondensation with oxaloacetate to form citric acid
• DPhotolysis releasing molecular oxygen

In oxidative phosphorylation, high-energy electrons from NADH and FADH2 pass down the inner mitochondrial electron transport chain. What is the direct source of energy that drives ATP synthesis by ATP synthase?

• AThe electrochemical proton (H+) gradient across the inner mitochondrial membrane
• BDirect transfer of a phosphate group from glucose to ADP
• CLight photon absorption by cytochrome oxidase
• DHydrolysis of GTP into GMP in the matrix

Under hypoxic (low oxygen) conditions in yeast, pyruvate undergoes ethanol fermentation. Why is fermentation essential for cell survival when oxygen is absent?

• AIt regenerates NAD+ so glycolysis can continue producing ATP
• BIt yields 36 additional ATP per glucose molecule
• CIt pumps protons into the mitochondrial intermembrane space
• DIt fixes inorganic atmospheric carbon into glucose

In the global carbon cycle, which biological process directly removes carbon dioxide gas from the atmosphere and incorporates it into organic biological macromolecules?

• APhotosynthesis by autotrophs
• BCellular respiration by heterotrophs
• CDecomposition by saprophytes
• DVolcanic outgassing

Atmospheric nitrogen (N2) cannot be used directly by plants. Which organism type converts N2 into usable ammonium (NH4+) in soil and legume root nodules?

• ANitrogen-fixing bacteria (such as Rhizobium)
• BMycorrhizal fungi
• CDenitrifying bacteria
• DHerbivorous insects

A population of Utah prairie dogs exhibits S-shaped (logistic) growth after colonizing a meadow. What ecological parameter limits the population size as it approaches environmental carrying capacity (K)?

• ADensity-dependent factors like food availability, burrows, and disease
• BInfinite availability of primary producer biomass
• CComplete elimination of interspecific competition
• DLinear exponential growth without resource constraints

In a Great Salt Lake marsh ecosystem, brine shrimp feed on unicellular green algae, and migrating American avocets feed on brine shrimp. If the green algae store 50,000 kJ of energy, approximately how much energy is transferred to the avocets?

• A500 kJ
• B5,000 kJ
• C45,000 kJ
• D50 kJ

An aquatic plant experiment measures oxygen production at increasing light intensities while keeping temperature and CO2 constant. The rate of O2 production increases steadily, then plateaus. What explains the plateau?

• ALight intensity is no longer the limiting factor; CO2 or enzyme capacity limits the rate
• BChloroplasts undergo cellular respiration and stop photosynthesizing
• CWater molecules are completely depleted in the plant tissue
• DLight energy begins to destroy ATP synthase enzymes

Why does an ecological energy pyramid always feature a wide base of producers and progressively narrower tiers for higher trophic levels?

• AEnergy is lost as metabolic heat and entropy increases at each trophic transfer step
• BTop carnivores have faster metabolic rates and create energy internally
• CDecomposers store 90% of all solar energy at the top of the pyramid
• DHigher trophic levels convert heat directly back into glucose

A high school athlete sprinting up a steep Utah trail experiences muscle fatigue due to anaerobic conditions. Which byproduct accumulates in skeletal muscle cells when oxygen demand exceeds delivery?

• ALactate (lactic acid)
• BEthanol
• CAcetyl-CoA
• DCitric acid

Students use respirometers to measure oxygen consumption in germinating pea seeds versus non-germinating pea seeds at 20°C. Why do germinating seeds consume significantly more O2?

• AGerminating seeds are actively growing and require high rates of cellular respiration to…
• BNon-germinating seeds perform photosynthesis instead of cellular respiration
• CGerminating seeds use O2 to synthesize starch from cellulose
• DNon-germinating seeds convert O2 into nitrogen gas via denitrification

What critical role do saprophytic fungi and soil bacteria play in maintaining ecosystem sustainability?

• AThey decompose dead organic matter, recycling essential inorganic nutrients back to produ…
• BThey convert solar radiant energy into chemical energy for primary consumers
• CThey eliminate the need for carbon dioxide in plant photosynthesis
• DThey trap 100% of ecosystem heat and convert it into biomass

Which trophic level forms the essential biological foundation of all terrestrial food webs by capturing solar energy?

• APrimary producers (autotrophs)
• BPrimary consumers (herbivores)
• CSecondary consumers (carnivores)
• DTertiary consumers (apex predators)

Severe multi-year drought in Utah reduces forage plant biomass in a mule deer habitat. How does this abiotic disturbance affect the carrying capacity (K) for the mule deer population?

• ACarrying capacity decreases because available food resources are reduced
• BCarrying capacity increases to compensate for deer mortality
• CCarrying capacity remains unchanged because K is a fixed constant
• DCarrying capacity drops to zero permanently, causing instant total extinction

How is the proton gradient across the thylakoid membrane coupled to ATP synthesis during photophosphorylation in chloroplasts?

• AProtons diffuse down their concentration gradient through ATP synthase, driving rotationa…
• BProtons pump electrons directly into NADP+ reductase via active transport
• CProtons combine with CO2 to form glucose inside the thylakoid lumen
• DProtons hydrolyze ATP into ADP to release light energy

According to the fluid mosaic model of cell membranes, what structural feature enables selective permeability while maintaining membrane flexibility?

• AAn amphipathic phospholipid bilayer with embedded, laterally moving proteins
• BA rigid, impenetrable wall of cellulose microfibrils
• CA solid monolayer of cholesterol locked in fixed positions
• DA triple layer of nucleic acids bonded by peptide links

Small nonpolar molecules like oxygen (O2) and carbon dioxide (CO2) cross the cell membrane effortlessly. Why can these specific molecules cross via simple diffusion without protein channels?

• AThey dissolve easily in the hydrophobic fatty acid core of the phospholipid bilayer
• BThey are actively pumped by ATP hydrolysis enzymes
• CThey bind to carbohydrate cell surface markers
• DThey carry strong electrical charges that attract lipid heads

Glucose molecules enter red blood cells down their concentration gradient using GLUT1 carrier proteins without expending cellular metabolic energy. Which transport mechanism is operating?

• AFacilitated diffusion
• BPrimary active transport
• CReceptor-mediated endocytosis
• DExocytosis

The sodium-potassium pump (Na+/K+ ATPase) maintains resting membrane potentials in animal nerve cells. What occurs during one catalytic cycle of this pump?

• A3 Na+ ions are pumped out of the cell and 2 K+ ions are pumped in, consuming 1 ATP
• B2 Na+ ions are pumped in and 3 K+ ions are pumped out, generating 1 ATP
• C3 Na+ ions and 3 K+ ions diffuse passively out of the cell
• D1 Na+ ion and 1 K+ ion undergo endocytosis together

A human red blood cell is placed in a 5% NaCl hypertonic saline solution. What net movement of water occurs, and what visual change happens to the cell?

• AWater moves out of the cell by osmosis; the cell shrivels (crenates)
• BWater moves into the cell by osmosis; the cell swells and bursts (lyses)
• CWater and NaCl move in equal amounts; the cell volume remains constant
• DSolutes leave the cell while water enters; the cell forms a cell plate

When plant root cells absorb water from a hypotonic soil environment, water enters the central vacuole. What prevents plant cells from bursting under high osmotic turgor pressure?

• AThe rigid extracellular cell wall made of cellulose
• BActive transport of water out by lysosomes
• CRapid destruction of aquaporin channel proteins
• DImmediate synthesis of hydrophobic cholesterol

Which organelle is composed of ribosomal RNA (rRNA) and proteins, functioning as the universal molecular machine for translating mRNA into polypeptide chains?

• ARibosome
• BMitochondrion
• CGolgi apparatus
• DPeroxisome

Secretory proteins synthesized on ribosomes bound to the Rough Endoplasmic Reticulum (RER) move next to which organelle for glycosylation, sorting, and packaging into secretory vesicles?

• AGolgi apparatus
• BNucleolus
• CSmooth Endoplasmic Reticulum
• DCentrosome

Mitochondria possess extensively folded inner membranes called cristae. How does this specific structural adaptation enhance mitochondrial function?

• AIt maximizes the surface area available for electron transport chains and ATP synthase co…
• BIt prevents protons from leaking out into the cytoplasm
• CIt allows chloroplasts to attach during cellular division
• DIt stores excess glucose as glycogen granules

Which plant cell organelle contains thylakoid membranes arranged in stacks called grana, surrounded by a fluid-filled matrix called the stroma?

• AChloroplast
• BMitochondrion
• CCentral vacuole
• DLeucoplast

Enzymes act as biological catalysts in cellular reactions. What primary mechanism allows an enzyme to dramatically accelerate the rate of a specific biochemical reaction?

• ALowering the activation energy required to reach the transition state
• BIncreasing the total free energy change (ΔG) of the overall reaction
• CAdding heat energy to the cell substrate solution
• DConverting endergonic reactions into exergonic reactions

A student measures enzyme activity at increasing temperatures. The reaction rate rises up to 37°C, then drops sharply to zero at 60°C. What structural change causes the loss of enzyme activity at 60°C?

• AThermal denaturation altering the enzyme's tertiary structure and active site shape
• BHydrolysis of the primary amino acid sequence into single amino acids
• CCompetitive binding of water molecules to the substrate
• DPermanent conversion of the enzyme into RNA

Human pepsin digests proteins in the acidic stomach (pH 2), whereas trypsin digests proteins in the neutral/basic small intestine (pH 8). What happens if trypsin is placed in a pH 2 solution?

• ATrypsin denatures because altered hydrogen bonding disrupts its active site shape
• BTrypsin increases its catalytic rate fourfold to match pepsin
• CTrypsin transforms into pepsin by changing its primary amino acid sequence
• DTrypsin synthesizes ATP from stomach acid protons

An enzyme-catalyzed reaction is conducted with a fixed enzyme concentration and steadily increasing substrate concentration. The reaction rate initially increases, then reaches a maximum velocity (Vmax). Why does the rate plateau?

• AAll enzyme active sites are fully saturated with substrate molecules
• BSubstrate molecules begin acting as non-competitive inhibitors
• CThe activation energy of the reaction rises to infinity
• DEnzyme molecules are completely destroyed by excess substrate

How does a competitive enzyme inhibitor differ functionally from a non-competitive (allosteric) inhibitor?

• ACompetitive inhibitors bind directly to the active site; non-competitive inhibitors bind…
• BCompetitive inhibitors destroy the substrate; non-competitive inhibitors destroy the prod…
• CCompetitive inhibition cannot be overcome by adding more substrate; non-competitive inhib…
• DCompetitive inhibitors are made of DNA; non-competitive inhibitors are made of lipid

During transcription in a eukaryotic cell nucleus, RNA polymerase reads the DNA template strand. In which direction is the single-stranded pre-mRNA molecule synthesized?

• A5' to 3' direction
• B3' to 5' direction
• CN-terminus to C-terminus direction
• DRandomly in both directions simultaneously

Before eukaryotic pre-mRNA leaves the nucleus for translation, it undergoes post-transcriptional processing. What modifications occur during this maturation process?

• AAddition of a 5' cap, addition of a 3' poly-A tail, and splicing out of non-coding introns
• BRemoval of all exons and ligation of remaining introns
• CAttachment of amino acids directly to the 5' end by ribosomes
• DConversion of all uracil (U) bases back into thymine (T) bases

During protein translation at the ribosome, what specific molecular interaction ensures that correct amino acids are added in the sequence specified by mRNA?

• AComplementary base pairing between the mRNA codon and the tRNA anticodon
• BCovalent peptide bonding between adjacent mRNA molecules
• CDirect binding of DNA polymerase to the ribosomal A site
• DPhosphorylation of ribosomal RNA by ATP synthase

The genetic code contains 64 possible 3-letter mRNA codons, but only 20 standard amino acids. What term describes this property of the genetic code, where multiple codons specify the same amino acid?

• ADegeneracy (or redundancy)
• BAmbiguity
• CUniversal overlapping
• DIncomplete dominance

Human kidney epithelial cells express specialized transmembrane channel proteins called aquaporins. What is the physiological function of aquaporins in cell membranes?

• AFacilitating rapid passive transport of water molecules across the membrane
• BActively pumping glucose against a 100-fold concentration gradient
• CSynthesizing lipid molecules for membrane repair
• DTransporting large proteins into the nucleus

Which eukaryotic organelle maintains an internal acidic pH (~4.5-5.0) and contains hydrolytic enzymes responsible for breaking down damaged organelles (autophagy) and engulfed pathogens?

• ALysosome
• BChloroplast
• CRough Endoplasmic Reticulum
• DNucleolus

Blood glucose homeostasis is maintained by endocrine pancreas hormones. Following a meal, elevated blood glucose triggers insulin release to promote glucose uptake. When fasting, glucagon triggers glycogen breakdown. What homeostatic control loop is operating?

• ANegative feedback loop
• BPositive feedback loop
• CFeed-forward destructive cascade
• DOpen-loop non-regulatory decay

Pancreatic acinar cells export digestive enzymes (like amylase and trypsinogen) into pancreatic ducts via vesicle fusion with the plasma membrane. Which bulk transport mechanism is used?

• AExocytosis
• BPinocytosis
• CPhagocytosis
• DSimple diffusion

A peptide hormone binds to a cell-surface G protein-coupled receptor (GPCR), initiating an intracellular signal transduction cascade involving cyclic AMP (cAMP) and protein kinase A (PKA). What is the primary purpose of such intracellular cascades?

• ATo amplify the extracellular signal and trigger specific cellular responses
• BTo mutate the cell's nuclear DNA genome
• CTo convert the peptide hormone into a lipid phospholipid
• DTo permanently stop all cellular protein synthesis

How do plant guard cells regulate stomatal opening to balance CO2 intake for photosynthesis with water loss through transpiration?

• AActive uptake of potassium ions (K+) causes water to enter guard cells by osmosis, making…
• BLoss of water causes guard cells to swell and seal the pore shut
• CGuard cells convert cellulose into starch to physically plug the opening
• DStomata remain open continuously regardless of environmental humidity or light

DNA is composed of two antiparallel polynucleotide strands wrapped in a double helix. Which chemical bonds link complementary nitrogenous bases across the center of the helix, and which link adjacent nucleotides along the sugar-phosphate backbone?

• AHydrogen bonds across bases; phosphodiester bonds along the backbone
• BPeptide bonds across bases; ionic bonds along the backbone
• CCovalent disulfide bonds across bases; hydrogen bonds along the backbone
• DMetallic bonds across bases; glycosidic bonds along the backbone

A sample of double-stranded DNA isolated from Utah native trout is analyzed and found to contain 28% Cytosine (C). According to Chargaff's rules, what percentage of Adenine (A) is present in this DNA sample?

• A22%
• B28%
• C44%
• D56%

During semi-conservative DNA replication, why is the leading strand synthesized continuously while the lagging strand is synthesized discontinuously in short Okazaki fragments?

• ADNA polymerase III can only add nucleotides to the 3' end of a growing strand (synthesizi…
• BHelicase unwinds the double helix in only one direction at a time
• CThe lagging strand lacks RNA primers
• DDNA ligase destroys the leading strand template