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Scio NSZ Biology study materials
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Scio NSZ Biology practice questions

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Question 1General Biology

Which organelle is the primary site of ATP synthesis in a eukaryotic cell?

  1. Mitochondrion Correct answer.
  2. Golgi apparatus
  3. Lysosome
  4. Ribosome

Explanation

Mitochondria carry out oxidative phosphorylation, using the electron transport chain and ATP synthase to generate most of the cell's ATP. Other organelles perform different specialized functions and are not the main ATP producers.

Question 2General Biology

A cell is placed in a hypertonic solution. What is the most likely immediate effect on an animal cell?

  1. It stays unchanged in volume
  2. It swells and may burst
  3. It builds a rigid cell wall
  4. It shrinks as water leaves Correct answer.

Explanation

In a hypertonic solution the solute concentration outside is higher than inside, so water moves out by osmosis. An animal cell loses water and shrinks.

Question 3General Biology

Which molecule carries the amino acids to the ribosome during translation?

  1. rRNA
  2. tRNA Correct answer.
  3. DNA polymerase
  4. mRNA

Explanation

Transfer RNA (tRNA) binds specific amino acids and delivers them to the ribosome, where its anticodon pairs with the mRNA codon. Messenger RNA carries the coding sequence, and ribosomal RNA is a structural and catalytic part of the ribosome.

Question 4General Biology

During which phase of mitosis do sister chromatids separate and move to opposite poles?

  1. Anaphase Correct answer.
  2. Metaphase
  3. Telophase
  4. Prophase

Explanation

In anaphase the cohesion holding sister chromatids is cleaved, and the separated chromosomes are pulled toward opposite spindle poles. Prophase and metaphase precede this separation, and telophase follows it.

Question 5General Biology

Which of the following is the main product of the light-dependent reactions of photosynthesis?

  1. Glucose
  2. Pyruvate
  3. ATP and NADPH Correct answer.
  4. Carbon dioxide

Explanation

The light-dependent reactions convert light energy into chemical energy stored as ATP and NADPH, which are then used in the Calvin cycle. Glucose is produced later from carbon fixation, not directly by the light reactions.

Question 6General Biology

Which blood vessel type has the thinnest walls to allow exchange of gases and nutrients with tissues?

  1. Artery
  2. Vein
  3. Aorta
  4. Capillary Correct answer.

Explanation

Capillaries have walls only one cell thick, which minimizes diffusion distance for exchange between blood and tissue fluid. Arteries, veins, and the aorta have thicker, multi-layered walls suited to pressure and transport.

Question 7General Biology

Which type of bond holds the two strands of a DNA double helix together?

  1. Disulfide bonds
  2. Ionic bonds
  3. Peptide bonds
  4. Hydrogen bonds Correct answer.

Explanation

Complementary bases on opposite strands pair through hydrogen bonds: adenine with thymine forms two, and guanine with cytosine forms three. These relatively weak bonds allow the strands to separate during replication and transcription.

Question 8General Biology

In Mendel's monohybrid cross between two heterozygous tall pea plants (Tt x Tt), what proportion of the offspring is expected to show the recessive phenotype?

  1. Three quarters
  2. One quarter Correct answer.
  3. One half
  4. All of them

Explanation

A Tt x Tt cross yields genotypes in a 1 TT : 2 Tt : 1 tt ratio. Only the tt genotype expresses the recessive phenotype, which is one quarter of the offspring.

Question 9General Biology

A woman who is a carrier of an X-linked recessive disorder has children with an unaffected man. What fraction of their sons is expected to be affected?

  1. None
  2. One quarter
  3. All
  4. One half Correct answer.

Explanation

Sons inherit their single X chromosome from the mother. A carrier mother has one normal and one affected X allele, so each son has a one-half chance of inheriting the affected allele and being affected.

Question 10General Biology

Which process produces genetic variation by exchanging segments between homologous chromosomes?

  1. Binary fission
  2. Osmosis
  3. Crossing over Correct answer.
  4. Translation

Explanation

Crossing over occurs during prophase I of meiosis, when non-sister chromatids of homologous chromosomes exchange segments. This recombination creates new combinations of alleles on a chromosome.

Question 11General Biology

An enzyme-catalyzed reaction is studied at increasing substrate concentrations. The rate rises and then levels off. What does the plateau indicate?

  1. The enzyme has been permanently destroyed
  2. All active sites are saturated with substrate Correct answer.
  3. The temperature has dropped to zero
  4. The substrate has become an inhibitor

Explanation

At high substrate concentration, essentially all enzyme active sites are occupied, so adding more substrate cannot increase the rate further. The plateau reflects enzyme saturation rather than enzyme destruction.

Question 12General Biology

Which statement best describes the role of the sodium-potassium pump in a neuron?

  1. It moves Na+ out and K+ in using ATP Correct answer.
  2. It transports only calcium ions
  3. It moves both ions with their gradients without energy
  4. It moves Na+ in and K+ out using ATP

Explanation

The sodium-potassium pump uses ATP to move three Na+ ions out of the cell and two K+ ions in, against their concentration gradients. This maintains the resting membrane potential and ion distribution.

Question 13General Biology

Aerobic respiration yields far more ATP per glucose molecule than anaerobic fermentation mainly because aerobic respiration does what?

  1. Occurs entirely in the cytoplasm
  2. Produces ATP directly from glucose without intermediates
  3. Uses oxygen as the final electron acceptor in the electron transport chain Correct answer.
  4. Skips glycolysis

Explanation

In aerobic respiration, oxygen accepts electrons at the end of the electron transport chain, allowing continued flow of electrons and extensive ATP production by oxidative phosphorylation. Fermentation lacks this terminal acceptor and yields little ATP.

Question 14General Biology

Which of the following best explains why a small population is more vulnerable to genetic drift than a large population?

  1. Small populations have higher mutation rates
  2. Large populations cannot undergo gene flow
  3. Chance fluctuations in allele frequencies have a larger effect in small populations Correct answer.
  4. Small populations always experience natural selection more strongly

Explanation

Genetic drift is random change in allele frequencies due to sampling; in small populations, random events can shift allele frequencies substantially from one generation to the next. In large populations these random effects tend to average out.

Question 15General Biology

Which level of protein structure is defined by the overall three-dimensional shape formed by folding of a single polypeptide chain?

  1. Tertiary Correct answer.
  2. Primary
  3. Quaternary
  4. Secondary

Explanation

Tertiary structure is the overall 3D conformation of one polypeptide, stabilized by interactions among side chains such as hydrogen bonds, hydrophobic interactions, and disulfide bonds. Secondary structure refers to local patterns like alpha helices and beta sheets.

Question 16General Biology

A dihybrid cross between two individuals heterozygous for both traits (AaBb x AaBb) assumes independent assortment. What phenotypic ratio is expected?

  1. 1:1
  2. 1:2:1
  3. 9:3:3:1 Correct answer.
  4. 3:1

Explanation

With independent assortment, each gene shows a 3:1 dominant-to-recessive ratio, and combining two genes multiplies these ratios to give 9:3:3:1. This ratio depends on the genes assorting independently.

Question 17General Biology

Which feature distinguishes prokaryotic cells from eukaryotic cells?

  1. Prokaryotes lack DNA
  2. Prokaryotes lack a membrane-bound nucleus Correct answer.
  3. Prokaryotes lack ribosomes
  4. Prokaryotes lack a plasma membrane

Explanation

Prokaryotic cells keep their genetic material in a nucleoid region without a surrounding nuclear membrane, whereas eukaryotic cells have a true nucleus. Prokaryotes still possess ribosomes, a plasma membrane, and DNA.

Question 18General Biology

In a food chain, what is the usual approximate efficiency of energy transfer from one trophic level to the next?

  1. About 10 percent Correct answer.
  2. About 1 percent
  3. About 50 percent
  4. About 90 percent

Explanation

Only a small fraction of energy at one trophic level is incorporated into biomass at the next; a commonly cited rule of thumb is about 10 percent. Most energy is lost as heat through metabolism.

Question 19General Biology

Which of the following is an example of a density-dependent factor limiting population growth?

  1. Competition for nesting sites Correct answer.
  2. A sudden volcanic eruption
  3. A seasonal drought
  4. A wildfire

Explanation

Density-dependent factors have effects that intensify as population density rises; competition for limited nesting sites is a classic example. Density-independent factors such as natural disasters affect populations regardless of density.

Question 20General Biology

Which type of selection favors individuals at both extremes of a phenotypic range and acts against intermediate phenotypes?

  1. Stabilizing selection
  2. Directional selection
  3. Disruptive selection Correct answer.
  4. Artificial selection

Explanation

Disruptive selection acts against intermediate phenotypes and favors both extremes, sometimes leading to bimodal distributions. Stabilizing selection favors intermediates, and directional selection favors one extreme.

Question 21General Biology

A mutation changes a single DNA base but the resulting protein has the same amino acid sequence as before. What is this called?

  1. Missense mutation
  2. Silent mutation Correct answer.
  3. Nonsense mutation
  4. Frameshift mutation

Explanation

A silent mutation changes a codon but, owing to the redundancy of the genetic code, does not change the amino acid specified. Missense and nonsense mutations alter the protein sequence or introduce a stop codon.

Question 22General Biology

In humans, which chromosome combination normally determines a male offspring?

  1. XO
  2. XY Correct answer.
  3. XX
  4. YY

Explanation

Human males typically have one X and one Y chromosome, while females have two X chromosomes. The Y chromosome carries the SRY gene that triggers male development.

Question 23General Biology

An experiment shows that a reaction proceeds faster when a cofactor is added. Which conclusion is best supported?

  1. The substrate concentration was reduced
  2. The cofactor is required for full enzyme activity Correct answer.
  3. The enzyme was denatured
  4. The enzyme does not require the cofactor

Explanation

If activity increases upon adding the cofactor, the cofactor is needed for the enzyme to function at full rate, acting as a helper molecule. This supports a requirement rather than showing the enzyme is unaffected.

Question 24General Biology

A population of insects develops resistance to an insecticide over several generations. Which mechanism best explains this outcome?

  1. Pre-existing resistant variants survive and reproduce more successfully Correct answer.
  2. The insecticide is diluted in the environment over time
  3. Individual insects gradually strengthen their immune systems
  4. The insecticide causes mutations that create resistance on demand

Explanation

Resistance arises because some individuals already carry variants that allow survival; the insecticide selects for these, and they leave more offspring. Selection acts on existing variation rather than directing new mutations.

Question 25General Biology

In a Hardy-Weinberg population, the frequency of a recessive allele is 0.2. What is the expected frequency of heterozygotes?

  1. 0.32 Correct answer.
  2. 0.04
  3. 0.16
  4. 0.64

Explanation

With q = 0.2, p = 0.8, and the heterozygote frequency is 2pq = 2(0.8)(0.2) = 0.32. The term q squared gives the homozygous recessive frequency, not the heterozygote frequency.

Question 26General Biology

Which organelle is the primary site of ATP production by oxidative phosphorylation in a eukaryotic cell?

  1. The Golgi apparatus
  2. The mitochondrion Correct answer.
  3. The lysosome
  4. The smooth endoplasmic reticulum

Explanation

The inner mitochondrial membrane houses the electron transport chain and ATP synthase, which together carry out oxidative phosphorylation. Other organelles listed handle packaging, degradation, or lipid synthesis rather than bulk ATP synthesis.

Question 27General Biology

Which molecule serves as the immediate energy currency that powers most cellular work?

  1. ATP Correct answer.
  2. Glucose
  3. Pyruvate
  4. NADH

Explanation

ATP couples exergonic reactions to endergonic ones by transferring a phosphate group, making it the direct energy currency of the cell. Glucose and NADH store energy that must first be converted to ATP before most cellular processes can use it.

Question 28General Biology

Which property of water allows insects such as water striders to move across a pond surface?

  1. Its surface tension from hydrogen bonding Correct answer.
  2. Its low density as a solid
  3. Its ability to act as a solvent
  4. Its high specific heat capacity

Explanation

Cohesive hydrogen bonds between water molecules create surface tension, a film strong enough to support small organisms. Specific heat, ice density, and solvent behavior are distinct properties not responsible for supporting weight at the surface.

Question 29General Biology

During which phase of the cell cycle does DNA replication occur?

  1. S phase Correct answer.
  2. M phase
  3. G2 phase
  4. G1 phase

Explanation

DNA synthesis takes place during S phase, which lies between the two gap phases of interphase. G1 and G2 are periods of growth and preparation, while M phase is when the replicated chromosomes are separated and the cell divides.

Question 30General Biology

A pure-breeding red-flowered plant is crossed with a pure-breeding white-flowered plant, and all the offspring have pink flowers. What pattern of inheritance does this demonstrate?

  1. Sex-linked inheritance
  2. Incomplete dominance Correct answer.
  3. Codominance
  4. Complete dominance

Explanation

In incomplete dominance the heterozygote shows an intermediate phenotype, here a blend of red and white pigment producing pink. Complete dominance would yield all red offspring, and codominance would show both colors distinctly rather than blended.

Question 31General Biology

What is the main function of the ribosome during gene expression?

  1. Translating mRNA into a polypeptide chain Correct answer.
  2. Replicating DNA before cell division
  3. Transcribing DNA into mRNA
  4. Splicing introns out of pre-mRNA

Explanation

Ribosomes read the mRNA codon sequence and assemble amino acids into a polypeptide according to the genetic code. Transcription, splicing, and replication are carried out by RNA polymerase, the spliceosome, and the replication machinery respectively.

Question 32General Biology

Which statement correctly describes the relationship between photosynthesis and cellular respiration?

  1. Respiration produces glucose, while photosynthesis breaks it down
  2. Both processes occur only in the dark
  3. Photosynthesis stores energy in organic molecules, while respiration releases energy from them Correct answer.
  4. Photosynthesis releases carbon dioxide, while respiration consumes it

Explanation

Photosynthesis uses light energy to build organic molecules and store energy, whereas respiration oxidizes those molecules to release usable energy. The two processes are complementary in the flow of matter and energy.

Question 33General Biology

In a pedigree, a trait appears in every generation and affects roughly half of the offspring of an affected parent regardless of sex. Which mode of inheritance is most consistent with this pattern?

  1. X-linked recessive
  2. Autosomal recessive
  3. Y-linked
  4. Autosomal dominant Correct answer.

Explanation

A trait in every generation with about half of offspring affected from an affected parent fits autosomal dominant inheritance, since each affected heterozygote transmits the allele with probability one-half. Autosomal recessive traits often skip generations, and the sex-independent pattern rules out sex-linked modes.

Question 34General Biology

Which structure connects the two sister chromatids of a chromosome and serves as the attachment point for spindle fibers?

  1. Chromatin
  2. Centromere Correct answer.
  3. Telomere
  4. Centriole

Explanation

The centromere is the constricted region where sister chromatids are joined and where the kinetochore assembles for spindle attachment. Telomeres protect chromosome ends, centrioles organize spindle poles, and chromatin describes the DNA-protein complex generally.

Question 35General Biology

A cell in a diploid organism has 24 chromosomes. How many chromosomes will each daughter cell contain after a normal mitotic division?

  1. 12
  2. 48
  3. 24 Correct answer.
  4. 6

Explanation

Mitosis preserves chromosome number, so each daughter cell receives a full diploid set identical to the parent cell, which is 24. Halving to 12 would occur only in meiosis, and 48 would result from a failure to divide the replicated sets.

Question 36General Biology

Which feature of the plasma membrane is best described by the fluid mosaic model?

  1. A single sheet of cellulose enclosing the cytoplasm
  2. A rigid, static layer of protein with no lipid component
  3. A solid barrier that permits no molecules to pass
  4. A dynamic bilayer of phospholipids with embedded and movable proteins Correct answer.

Explanation

The fluid mosaic model describes the membrane as a fluid phospholipid bilayer in which proteins are embedded and can move laterally. This dynamic arrangement allows selective permeability and protein function within the membrane.

Question 37General Biology

Two species of finch live on the same island and eat seeds of similar size, but one has a thick beak suited to hard seeds and the other a slender beak suited to soft seeds. Which concept best explains how these differences reduce competition?

  1. Carrying capacity overshoot
  2. Primary succession on bare rock
  3. Competitive exclusion through resource partitioning Correct answer.
  4. Mutualism between the two species

Explanation

Resource partitioning lets species divide available resources and thereby reduce direct competition, often through character displacement such as differing beak morphology. Competitive exclusion would instead drive one species to local extinction if niches fully overlapped.

Question 38General Biology

A segment of mRNA has the sequence 5'-AUG GCA UAA-3'. Using the standard genetic code, what polypeptide results?

  1. Alanine–methionine, continuing past the stop codon
  2. No polypeptide, because the first codon is a stop codon
  3. Methionine only, because the second codon is a stop
  4. Methionine–alanine, terminating at the stop codon Correct answer.

Explanation

AUG codes for methionine and acts as the start codon, GCA codes for alanine, and UAA is a stop codon that ends translation. The result is a dipeptide of methionine and alanine.

Question 39General Biology

In a population at Hardy-Weinberg equilibrium, a deleterious recessive allele is maintained at a low but stable frequency. Which condition most plausibly accounts for its persistence?

  1. Assortative mating removes all recessive homozygotes
  2. The recessive allele mutates into the dominant allele each generation
  3. The population is extremely small and inbred
  4. Heterozygotes carry the allele without expressing the deleterious phenotype Correct answer.

Explanation

Recessive deleterious alleles can persist because heterozygous carriers are phenotypically normal and are not removed by selection, so the allele is hidden from selection in heterozygotes. This balancing of selection against homozygotes keeps the allele at a low equilibrium frequency.

Question 40General Biology

A researcher finds that a metabolic reaction stops when a structural analog of the substrate is added, and increasing substrate concentration restores activity. Which conclusion is best supported?

  1. The analog is a noncompetitive inhibitor binding at an allosteric site
  2. The analog is an essential cofactor for the reaction
  3. The analog is a competitive inhibitor binding at the active site Correct answer.
  4. The analog denatures the enzyme irreversibly

Explanation

Reversal of inhibition by raising substrate concentration is the hallmark of competitive inhibition, in which the inhibitor competes with substrate for the active site. Noncompetitive inhibitors bind elsewhere and are not overcome by additional substrate.

Question 41Cell Biology

Which structure controls the passage of substances into and out of a eukaryotic cell?

  1. Cell wall
  2. Nuclear envelope
  3. Plasma membrane Correct answer.
  4. Cytoskeleton

Explanation

The plasma membrane is a selectively permeable phospholipid bilayer with embedded proteins that regulate transport. It forms the boundary between the cytoplasm and the external environment.

Question 42Cell Biology

During which phase of mitosis do sister chromatids separate and move toward opposite poles?

  1. Metaphase
  2. Anaphase Correct answer.
  3. Prophase
  4. Telophase

Explanation

In anaphase, cohesin is cleaved and sister chromatids are pulled apart by spindle fibres toward opposite poles. This follows their alignment at the metaphase plate.

Question 43Cell Biology

Which molecule serves as the immediate energy currency of the cell, coupling exergonic and endergonic reactions?

  1. Pyruvate
  2. Glucose
  3. ATP Correct answer.
  4. NADH

Explanation

ATP hydrolysis releases free energy that drives many endergonic processes, making it the cell's direct energy currency. Glucose and NADH store energy but must be processed before use.

Question 44Cell Biology

Which of the following is a function of the smooth endoplasmic reticulum?

  1. Translation of secretory proteins
  2. Synthesis of lipids and detoxification Correct answer.
  3. Replication of DNA
  4. Assembly of ribosomal subunits

Explanation

The smooth ER lacks ribosomes and is specialized for lipid and steroid synthesis, detoxification, and calcium storage. Protein translation occurs on the rough ER.

Question 45Cell Biology

What is the main role of the enzyme DNA polymerase during replication?

  1. Sealing nicks in the sugar-phosphate backbone
  2. Unwinding the double helix
  3. Joining nucleotides to the growing strand Correct answer.
  4. Synthesizing RNA primers

Explanation

DNA polymerase adds deoxynucleotides complementary to the template strand, extending the new DNA chain in the 5' to 3' direction. Unwinding and primer synthesis are performed by other enzymes.

Question 46Cell Biology

Which property of the phospholipid bilayer allows small nonpolar molecules to diffuse across it readily?

  1. Its net negative charge
  2. Its hydrophobic interior Correct answer.
  3. Its rigid cholesterol layer
  4. Its high protein content

Explanation

The fatty acid tails form a hydrophobic core that small nonpolar molecules such as oxygen can dissolve into and cross. Polar and charged substances require transport proteins.

Question 47Cell Biology

A student observes a cell with a rigid outer layer, chloroplasts, and a large central vacuole. Which cell type is this most likely to be?

  1. Animal epithelial cell
  2. Fungal cell
  3. Bacterial cell
  4. Plant cell Correct answer.

Explanation

Chloroplasts and a large central vacuole bounded by a cell wall are characteristic features of plant cells. Bacteria lack chloroplasts and a large vacuole, and animal cells lack a rigid wall and chloroplasts.

Question 48Cell Biology

In a reaction catalysed by an enzyme, what is the effect of the enzyme on the activation energy and the equilibrium constant?

  1. It lowers activation energy and leaves the equilibrium constant unchanged Correct answer.
  2. It lowers activation energy and changes the equilibrium constant
  3. It raises activation energy and leaves the equilibrium constant unchanged
  4. It leaves activation energy unchanged and changes the equilibrium constant

Explanation

Enzymes accelerate reactions by lowering the activation energy through stabilization of the transition state. They do not alter the free-energy difference between substrates and products, so the equilibrium constant is unchanged.

Question 49Cell Biology

A cell is treated with a drug that blocks the sodium-potassium pump. What is the most direct consequence for the resting membrane potential?

  1. It gradually depolarizes as ion gradients run down Correct answer.
  2. It becomes more negative as potassium accumulates
  3. It is unaffected because the pump is electrically neutral
  4. It reverses instantly to a positive value

Explanation

The pump maintains the sodium and potassium gradients that underlie the resting potential. Blocking it allows gradients to dissipate, so the membrane potential drifts toward zero, i.e. depolarizes.

Question 50Cell Biology

Which statement best describes the role of the Golgi apparatus in the secretory pathway?

  1. It modifies and sorts proteins received from the ER Correct answer.
  2. It synthesizes proteins destined for secretion
  3. It degrades proteins delivered from the cytosol
  4. It transcribes mRNA for secreted proteins

Explanation

The Golgi receives vesicles from the ER and carries out post-translational modifications such as glycosylation, then sorts proteins to their destinations. Synthesis occurs on the ER and transcription in the nucleus.