Final Practice Exam

During DNA replication, a new strand is sometimes built in separate short pieces. Which enzyme seals the backbone to join those pieces into one continuous strand?

Select one.

• Helicase, which unzips the helix at an origin of replication
• Catalase, which splits hydrogen peroxide into water and oxygen
• DNA polymerase, which adds nucleotides and proofreads
• DNA ligase, which seals the backbone

Read from its 5′ end, an mRNA is AUG UAU CCC UGA, coding Met–Tyr–Pro and then stop. A point mutation turns UAU into UUU, which codes for phenylalanine (Phe). What kind of mutation is this?

Select one.

• Silent, because one base changed and the chain keeps Tyr
• Nonsense, because UUU is an early stop codon
• Frameshift, because one base was swapped for another
• Missense, because Tyr is replaced by Phe

Both CCC and CCU code for proline (Pro). A point mutation changes a CCU codon in a gene's mRNA to CCC. What happens to the protein at that position?

Select one.

• Translation ends early, because the reading frame shifts
• It still has Pro, because proline has more than one codon
• It loses an amino acid, because CCC is a stop codon
• It gains Ala, because any base change swaps the amino acid

In meiosis II, each of the two cells made by meiosis I divides again. What separates and moves to opposite poles in this second division?

Select one.

• The homologous chromosomes of each pair
• The cytoplasm only, with no chromosome movement
• Whole sets of chromosomes, copied once more
• The sister chromatids of each chromosome

Red and white snapdragons produce pink offspring, an example of codominance, since each petal shows red and white in full.

True or false.

• True
• False

In an illustrative animal species, a body cell is diploid, with 18 chromosomes in 9 pairs. Which describes a sperm cell made by meiosis in this species?

Select one.

• Diploid, with 18 chromosomes, the same as a body cell
• Diploid, with 36 chromosomes ready for fertilization
• Haploid, with 9 chromosomes, one from each pair
• Haploid, with 9 half-chromosomes cut from the 18

In a eukaryotic cell, transcription, the step that copies a gene into mRNA, happens at the ribosomes in the cytoplasm.

True or false.

• True
• False

A picture of a liver cell's chromosomes sorts them into matched pairs. In each pair the two chromosomes have the same length and the same genes at the same positions, though they may hold different alleles. What is each matched pair called?

Select one.

• Homologous chromosomes
• Sister chromatids
• Daughter chromosomes from mitosis
• Nonsister chromatids

In the standard genetic code, 61 codons specify amino acids and the other 3 are stop codons. How many codons does the code contain in all?

Select one.

• 64
• 58
• 61
• 20

A field study zooms out from one deer to the whole planet. Which sequence runs from the smallest of these levels of organization to the largest?

Select one.

• organism, community, population, ecosystem, biosphere
• organism, population, community, ecosystem, biosphere
• population, organism, community, ecosystem, biosphere
• organism, population, ecosystem, community, biosphere

An illustrative cube-shaped cell measures 2 units on each edge. Its six faces give 6 × 2 × 2 = 24 square units of surface, and it encloses 2 × 2 × 2 = 8 cubic units of volume. Reduced to lowest terms, what is the ratio of surface area to volume?

Select one.

• 3:1, from 24 ÷ 8 = 3
• 24:8, left unreduced as surface to volume
• 8:24, from dividing 8 by 24
• 12:1, from 24 ÷ 2 = 12

RNA polymerase copies a template strand written 5′-TTATCCAGGCAT-3′. Which mRNA, written base by base beneath the template, does it make?

Select one.

• 3′-AATAGGTCCGTA-5′
• 3′-AAUAGGTCCGUA-5′
• 3′-AAUAGGUCCGUA-5′
• 3′-UUAUCCAGGCAU-5′

Algae floating in a sunlit pond make their own food. Which set names the inputs that photosynthesis uses?

Select one.

• Glucose, oxygen, and light energy
• Oxygen, water, and light energy
• Carbon dioxide, glucose, and minerals
• Carbon dioxide, water, and light energy

A pond freezes at its surface in winter while fish keep swimming in liquid water beneath. What lets the ice form a layer on top?

Select one.

• Freezing strips hydrogen atoms off, making each molecule lighter
• Cold water contains fewer molecules, so frozen water weighs less
• Hydrogen bonds hold ice in an open lattice that is less dense
• Air bubbles get trapped inside every ice crystal and lift it up

A tumor-suppressor protein that is mutated in roughly half of human cancers acts as a guard on the cell cycle. What does it normally do when a cell's DNA is damaged?

Select one.

• It speeds the cycle forward so the damaged cell divides sooner
• It halts the cycle for repair, or triggers apoptosis if needed
• It replicates the damaged DNA during the S phase
• It builds a cleavage furrow so the damaged cell splits in two

Near the end of mitosis, a fresh envelope forms around each of the two sets of chromosomes. Which organelle is being rebuilt, and what is its job?

Select one.

• The lysosome, which digests worn-out parts of the cell
• The Golgi apparatus, which modifies, sorts, and packages proteins
• The nucleus, which holds the DNA and directs the cell
• The mitochondrion, which makes ATP by cellular respiration

At the ribosome, a tRNA's anticodon base-pairs with a three-base codon. Which molecule carries that codon?

Select one.

• The mRNA
• The tRNA
• The DNA coding strand
• The small ribosomal subunit

A DNA strand reads 3′-GATCCA-5′. Which sequence is the strand that pairs with it in a double helix?

Select one.

• 5′-GATCCA-3′
• 5′-CTAGGT-3′
• 5′-CUAGGU-3′
• 5′-TGGATC-3′

A sample of white vinegar measures about pH 3, and a glass of tap water measures about pH 7. How many times more hydrogen ions does the vinegar contain?

Select one.

• 4 times, because 7 minus 3 is 4
• 40 times, because each step adds ten
• 10,000 times, because 4 steps give 10⁴
• 1,000 times, because 3 steps give 10³

A student's model helix includes a rung joining cytosine to thymine. Why would that rung not fit a real DNA molecule?

Select one.

• Both are pyrimidines with a single ring, so the rung would be too narrow
• Thymine is found only in RNA, never in DNA
• Both are purines with a double ring, so the rung would be far too wide
• The rung would need five hydrogen bonds to hold together

Germ theory is called a theory in biology. What does the word theory mean in that name?

Select one.

• A hunch that nobody has put to a test so far
• A broad explanation supported by many repeated tests
• One prediction that was tested a single time
• An idea that no new evidence could ever revise

Viewed under a microscope, a dividing cell has its chromosomes arranged in a single line across its center. Which phase of mitosis does it show?

Select one.

• Prophase
• Anaphase
• Metaphase
• Telophase

An acorn grows into an oak tree that weighs several tonnes. Where does most of the mass of its wood come from?

Select one.

• Carbon from carbon dioxide in the air, with water
• Soil the roots pull up as the tree grows
• Sunlight converted straight into wood
• Minerals that arrive dissolved in rain

A daughter shows an X-linked recessive trait. What must be true of her father?

Select one.

• He shows the trait, because his only X carried the allele to her
• He is an unaffected carrier, like many mothers
• Nothing can be said, because both of her alleles came from her mother
• He passed the allele to her on his Y chromosome

An illustrative gel runs a size ladder with bands at 300, 750, 1,500, and 3,000 bp, and the DNA moves from the wells toward the positive electrode. Which band ends up farthest from the wells?

Select one.

• The 3,000 bp band, because larger fragments carry more charge
• The 1,500 bp band, because middle sizes move most freely
• All four bands travel the same distance, since all DNA is negative
• The 300 bp band, as smaller fragments slip through the gel faster

In an illustrative count from a plant root tip, 200 cells are scored: 150 in interphase, 24 in prophase, 10 in metaphase, 6 in anaphase, and 10 in telophase. What percent of the cells are in mitosis (the mitotic index)?

Select one.

• 25%
• 75%
• 12%
• 33%

A cell is cut off from its oxygen supply, and soon its electron transport chains stall. What job was the missing oxygen doing?

Select one.

• Accepting electrons at the end of the chain and joining hydrogen to form water
• Splitting glucose into two pyruvate molecules out in the cytoplasm
• Turning into the carbon dioxide that the lungs breathe out with each exhaled breath
• Serving as a fuel stored in the matrix for the citric acid cycle to use

Crossing over trades segments of DNA between chromatids. Which chromatids make the trade, and in which stage does it happen?

Select one.

• Sister chromatids of one chromosome, in anaphase II
• Nonsister chromatids of a homologous pair, in prophase I
• Chromatids of any two chromosomes, during the S phase
• Nonsister chromatids of a homologous pair, in telophase II

To model a cross of two Tt parents, a class flips two coins 200 times (illustrative run) and records 47 TT, 103 Tt, and 50 tt. Which conclusion about the phenotypes is accurate?

Select one.

• 150 dominant to 50 recessive, which reduces to 3:1
• 47 dominant to 153 recessive, since only TT shows the dominant trait
• The phenotypes run 47 : 103 : 50, close to 1:2:1
• 103 dominant to 97 recessive, since only Tt shows the dominant trait

A runner says, "This sports drink gives my muscles brand-new energy." Which statement corrects the claim with the first law of thermodynamics?

Select one.

• Muscles create a small amount of new energy from every sip.
• Muscles destroy the drink's energy and give it off as heat instead.
• Its chemical energy is captured and converted, never created.
• Energy appears only when an enzyme supplies it to a reaction.

Two unknown cells each have ribosomes, cytoplasm, DNA, and a plasma membrane. Which observation tells a microbiologist which one is a bacterium?

Select one.

• Whether the DNA is enclosed in a membrane-bound nucleus
• Whether there are ribosomes present to make proteins
• Whether a plasma membrane surrounds the whole cell
• Whether there is any DNA anywhere inside the cell

A single extra C is inserted right after AUG in an mRNA that reads, from its 5′ end, AUG GGA UUU UAG. The changed mRNA reads AUG CGG AUU UUA plus a leftover G. Which statement describes this mutation?

Select one.

• A silent change, since the code has several codons per amino acid
• A change to the second amino acid only, since one base was added
• A frameshift: each codon after AUG changes and the stop is lost
• A nonsense change, since the protein now ends right after Met

In an illustrative test of a plant enzyme (constructed data, not real), the average foam was 3 cm in an ice bath at about 4 °C, 7 cm at about 25 °C, 12 cm at about 35 °C, and 0 cm after boiling at about 100 °C and cooling. Which explanation fits the ice-bath and boiled results?

Select one.

• Both the ice-bath and boiled samples were denatured, so neither one can recover.
• The boiled sample was tested while still too cold, so it only appears inactive.
• The ice bath slowed the enzyme, which would recover once warmed; boiling denatured it.
• A higher temperature always means a faster rate, so the boiled zero is a failed trial.

When phospholipids are added to water, they arrange themselves into a two-layer sheet. Where do their hydrophobic tails end up?

Select one.

• Pointing into the water along the outer surface
• Pointing into the water along the inner surface
• Packed in the middle, shielded from water by the heads
• Sticking out into the water from both surfaces

A newly made protein folds into its working form. Which sequence names the levels of protein structure from the simplest to the most complex?

Select one.

• Tertiary, secondary, primary, then quaternary
• Primary, secondary, tertiary, then quaternary
• Primary, quaternary, secondary, then tertiary
• Secondary, tertiary, primary, then quaternary

A beetle population meets a new predator that hunts by sight. Why does the variation produced by meiosis and fertilization affect whether this population can adapt?

Select one.

• Each beetle can choose to change its color once it sees the predator
• Meiosis makes every offspring identical, which steadies the population
• Natural selection acts only on body cells that divide by mitosis
• Selection can only favor traits that some beetles already carry

One stomach muscle cell can contract, but only the whole stomach can churn and mix a meal. What does the churning show?

Select one.

• A trait that each separate cell shows fully by itself
• The dependent variable of a controlled experiment
• A hypothesis that no experiment could ever falsify
• An emergent property that appears at the organ level

An illustrative gelatin cube used as a model cell is remade with its edge lengthened from 2 units to 6 units. How does its surface-area-to-volume ratio change, and why?

Select one.

• It climbs, because the bigger cube has far more surface
• It drops, because volume increases faster than surface area
• It holds steady, since surface and volume both increase
• It drops, because the cube's surface area gets smaller

In pea plants, the allele R for round seeds is dominant over r for wrinkled seeds. A plant carries two copies of r. Which description of this plant is accurate?

Select one.

• Genotype rr; heterozygous; shows the dominant round trait
• Phenotype rr; homozygous; shows a blend of round and wrinkled
• Genotype Rr; homozygous; shows the recessive wrinkled trait
• Genotype rr; homozygous; shows the recessive wrinkled trait

For a recessive allele carried on the X chromosome, which of these statements hold? Select all that apply.

Select every option that applies.

• A female with one copy of the allele is an unaffected carrier
• A male with one copy of the allele shows the trait
• Fathers pass the allele to their sons
• The trait shows up far more often in males than in females
• A male needs two copies of the allele to show the trait