Question 1

Which property of water is primarily responsible for the ability of trees to transport water from their roots to their leaves via the xylem, and what is the molecular basis for this property?

Accepted Answer

Cohesion; due to hydrogen bonds forming between water molecules.

Question 2

A patient is given an intravenous solution that is 2% NaCl. What will happen to their red blood cells, and why?

Accepted Answer

Cells will shrink because the solution is hypertonic, causing water to leave the cells by osmosis.

Question 3

Which of the following best explains why steroid hormones like testosterone can enter cells and alter gene expression, while peptide hormones like insulin cannot?

Accepted Answer

Steroid hormones are lipid-soluble and diffuse through the plasma membrane to bind intracellular receptors; peptide hormones are water-soluble and bind to cell surface receptors.

Question 4

During cellular respiration, which molecule acts as the final electron acceptor in the electron transport chain, and what is the main product formed?

Accepted Answer

O$$_2$$; H$$_2O$$

Question 5

A mutation causes the Na$$^+/K$^+$$ pump in a neuron to stop functioning. What is the most immediate effect on the neuron's membrane potential?

Accepted Answer

The resting membrane potential drifts toward zero (depolarizes) as ion gradients dissipate.

Question 6

Which of the following scenarios best illustrates positive feedback in endocrine regulation?

Accepted Answer

Infant suckling increases oxytocin release, which increases milk ejection, leading to more suckling and further oxytocin release.

Question 7

Which of the following best describes the main difference between the rising and falling phases of the neuronal action potential?

Accepted Answer

Rising phase is due to Na$$^+$$ influx through voltage-gated channels; falling phase begins when Na$$^+$$ channels inactivate and K$$^+$$ channels open.

Question 8

A genetic disorder causes a loss-of-function mutation in both copies of the p53 gene. What is the most likely cellular consequence?

Accepted Answer

Cells with DNA damage will continue to divide, increasing cancer risk.

Question 9

Which of the following is a direct result of the cyclic electron flow in the light reactions of photosynthesis?

Accepted Answer

Production of ATP only, with no NADPH or O$$_2$$ generated.

Question 10

Which of the following best explains why ice floats on liquid water, and what is the biological significance of this property?

Accepted Answer

Ice is less dense because hydrogen bonds in ice form a crystalline lattice, spacing molecules farther apart; this insulates aquatic life in winter.

Question 11

A cell is placed in a solution and swells until it bursts. Which of the following best describes the tonicity of the solution relative to the cell, and the direction of water movement?

Accepted Answer

The solution is hypotonic; water moves into the cell.

Question 12

Which of the following is a key feature of the endosymbiotic theory for the origin of mitochondria?

Accepted Answer

Mitochondria have a double membrane, their own circular DNA, and 70S ribosomes.

Question 13

Which of the following best describes the role of the operator in a bacterial operon?

Accepted Answer

It is the DNA sequence where a repressor protein can bind to block transcription.

Question 14

A muscle cell is unable to relax after contraction, resulting in rigor mortis. Which molecule is most directly responsible for detaching the myosin head from actin during the cross-bridge cycle?

Accepted Answer

ATP

Question 15

Which of the following best explains why the genetic code is described as 'redundant but not ambiguous'?

Accepted Answer

Multiple codons can specify the same amino acid, but each codon specifies only one amino acid.

Question 16

Which of the following is a direct effect of histone acetylation on chromatin structure and gene expression in eukaryotes?

Accepted Answer

Acetylation loosens chromatin into euchromatin, making genes accessible for transcription.

Question 17

A patient with a mutation in the gene encoding the enzyme acetylcholinesterase is likely to experience which of the following effects at the neuromuscular junction?

Accepted Answer

Prolonged muscle contraction due to excess acetylcholine in the synaptic cleft.

Question 18

Which of the following best describes the mechanism by which G protein-coupled receptors (GPCRs) amplify a signal inside a cell?

Accepted Answer

GPCRs activate G proteins, which then activate enzymes like adenylyl cyclase to produce second messengers such as cAMP, amplifying the signal.

Comprehensive Biology Final Exam Study Guide

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