IB Biology Quiz: Understand Chemical Signalling
20 questions · exam conditions
0:00
Understand Chemical SignallingQuestion 1 of 20

In a signal transduction pathway initiated by glucagon, a G-protein activates adenylyl cyclase, which produces cyclic AMP (cAMP). The cAMP then activates Protein Kinase A (PKA). What is the direct function of activated PKA in the subsequent steps of this cascade?

To act as a second messenger, amplifying the signal by diffusing rapidly throughout the cytoplasm.
To phosphorylate specific intracellular proteins, thereby altering their activity and eliciting a cellular response.
To bind to DNA in the nucleus and directly initiate the transcription of genes related to glucose metabolism.
To dephosphorylate target enzymes, reversing the effects of insulin signalling by removing phosphate groups.
← Back to quizzes

IB Biology Quiz

IB Biology Quiz: Understand Chemical Signalling

Practice Understand Chemical Signalling in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Chemical Signalling, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

In a signal transduction pathway initiated by glucagon, a G-protein activates adenylyl cyclase, which produces cyclic AMP (cAMP). The cAMP then activates Protein Kinase A (PKA). What is the direct function of activated PKA in the subsequent steps of this cascade?

  1. To act as a second messenger, amplifying the signal by diffusing rapidly throughout the cytoplasm.
  2. To phosphorylate specific intracellular proteins, thereby altering their activity and eliciting a cellular response. (correct answer)
  3. To bind to DNA in the nucleus and directly initiate the transcription of genes related to glucose metabolism.
  4. To dephosphorylate target enzymes, reversing the effects of insulin signalling by removing phosphate groups.
Explanation: The function of a protein kinase, such as PKA, is to catalyze the transfer of a phosphate group from ATP to a specific substrate protein. This phosphorylation changes the conformation and activity of the target protein, continuing the signal cascade.

Question 2

An athlete is illicitly taking a synthetic anabolic steroid that mimics testosterone. How would this affect the natural regulation of testosterone production via the hypothalamic-pituitary-gonadal axis?

  1. The synthetic steroid would stimulate the hypothalamus and pituitary, leading to an overproduction of natural testosterone through positive feedback.
  2. The synthetic steroid would inhibit the hypothalamus and pituitary, leading to reduced GnRH and LH secretion and subsequent atrophy of the testes. (correct answer)
  3. The synthetic steroid would have no effect on the hypothalamus or pituitary but would compete with natural testosterone for receptors in muscle tissue.
  4. The synthetic steroid would cause the pituitary to release more FSH but less LH, resulting in increased sperm production but lower testosterone.
Explanation: High levels of the exogenous steroid mimic testosterone, which exerts strong negative feedback on the hypothalamus (reducing GnRH release) and the anterior pituitary (reducing LH release). Reduced LH stimulation of the testes leads to decreased natural testosterone production and testicular atrophy.

Question 3

Adrenaline circulates throughout the body but triggers a 'fight or flight' response only in specific target cells like liver and muscle cells. What is the fundamental basis for this cellular specificity?

  1. Non-target cells have enzymes in their plasma membrane that rapidly degrade adrenaline before it can act.
  2. The circulatory system uses specialized capillaries to selectively deliver adrenaline only to the target tissues.
  3. Target cells possess specific transmembrane receptor proteins that recognize and bind to adrenaline. (correct answer)
  4. Non-target cells lack the basic second messenger molecules, such as cAMP, that are required for the response.
Explanation: The specificity of hormonal action is determined by the presence of specific receptors on or in target cells. Cells without the correct receptor for a particular hormone will not respond to it, even if they are exposed to the hormone.

Question 4

When a ligand binds to a G-protein coupled receptor (GPCR), a conformational change occurs in the receptor. What is the immediate, direct consequence of this change inside the cell?

  1. The receptor phosphorylates itself on tyrosine residues, activating intracellular kinase domains.
  2. The receptor opens an integrated ion channel, allowing an influx of calcium ions to act as second messengers.
  3. The receptor binds to an adjacent G-protein, causing the G-protein to exchange its bound GDP for a GTP. (correct answer)
  4. The receptor-ligand complex is internalized and moves to the nucleus to act as a transcription factor.
Explanation: The activated GPCR acts as a guanine nucleotide exchange factor (GEF). It binds to the inactive G-protein (bound to GDP) and facilitates the release of GDP and the binding of GTP, thereby activating the G-protein.

Question 5

Cholera toxin modifies G-proteins in intestinal cells so they are unable to hydrolyze GTP to GDP, causing them to remain permanently active. What is a sustained cellular consequence of this toxin's action?

  1. Persistent inactivation of adenylyl cyclase, leading to critically low levels of intracellular cAMP.
  2. Continuous activation of protein kinases, leading to constant phosphorylation of ion channel proteins. (correct answer)
  3. The cell surface receptors for the relevant hormone would be over-expressed to compensate for the signal.
  4. The cellular response would be terminated prematurely due to rapid degradation of all second messengers.
Explanation: A G-protein that is permanently active will continuously stimulate its target, adenylyl cyclase. This leads to high, sustained levels of cAMP, which in turn keeps Protein Kinase A (PKA) constantly active. Activated PKA phosphorylates ion channels (CFTR), leading to massive ion and water efflux from the cells.

Question 6

The anterior pituitary produces several tropic hormones. Which of the following is the defining characteristic of a tropic hormone?

  1. It is a steroid hormone that directly regulates metabolic processes in various non-endocrine tissues.
  2. It exclusively initiates positive feedback loops that continue until an external stimulus is removed.
  3. It circulates in the blood but its only target cells are located within the hypothalamus.
  4. It targets another endocrine gland, stimulating it to grow and secrete its own distinct hormones. (correct answer)
Explanation: The definition of a tropic hormone is one that has another endocrine gland as its target. Examples include Thyroid-stimulating hormone (TSH) which targets the thyroid, and Adrenocorticotropic hormone (ACTH) which targets the adrenal cortex.

Question 7

An individual is under extreme, prolonged stress. The hypothalamus has been releasing corticotropin-releasing hormone (CRH) for an extended period. What is the most likely downstream hormonal consequence?

  1. The posterior pituitary releases high levels of cortisol, a peptide hormone.
  2. The anterior pituitary releases ACTH, leading to high levels of cortisol from the adrenal medulla.
  3. The adrenal cortex releases high levels of adrenaline, a steroid hormone, which alters gene expression.
  4. The anterior pituitary releases ACTH, leading to high levels of cortisol from the adrenal cortex. (correct answer)
Explanation: The correct pathway for the long-term stress response is: Hypothalamus releases CRH -> Anterior Pituitary releases ACTH (a tropic hormone) -> Adrenal Cortex is stimulated by ACTH to release cortisol (a steroid hormone).

Question 8

Signal amplification is a key feature of many hormonal pathways. Which of the following events contributes most directly to the amplification of the signal initiated by a single molecule of a peptide hormone?

  1. A single hormone-receptor complex binding sequentially to multiple, different sites on the DNA.
  2. A single active receptor protein activating multiple G-proteins before the hormone unbinds. (correct answer)
  3. A single second messenger molecule, like cAMP, activating multiple types of transcription factors simultaneously.
  4. A single hormone molecule being repeatedly transported in and out of the target cell to bind the receptor multiple times.
Explanation: Amplification occurs at several steps. A primary step is when one activated receptor can activate many G-protein molecules. Each G-protein then activates an enzyme (like adenylyl cyclase), which can produce many second messenger molecules, further amplifying the signal.

Question 9

While most hormonal systems maintain homeostasis via negative feedback, some use positive feedback. Which statement accurately describes a key aspect of a positive feedback loop in an endocrine context?

  1. The final product of the pathway stabilizes the system by inhibiting the secretion of the initial hormone.
  2. The response to a stimulus acts to reduce or counteract the original stimulus, maintaining a stable set point.
  3. The response to a stimulus reinforces and amplifies the stimulus, leading to an escalating, often climactic, event. (correct answer)
  4. The system constantly oscillates around a set point due to time-delayed inhibitory signals from the target organ.
Explanation: Positive feedback is a mechanism where the output of a system enhances or amplifies the original stimulus. This drives the system further from its initial state and is used for processes that need to be rapidly completed, such as oxytocin's role in uterine contractions during childbirth.

Question 10

In some signalling pathways, the binding of a hormone leads to the release of Ca²⁺ from the endoplasmic reticulum into the cytosol. What is the primary significance of this sharp increase in cytosolic Ca²⁺ concentration?

  1. It directly causes the cell membrane to hyperpolarize, preventing further signalling.
  2. It acts as a second messenger, binding to and altering the activity of specific proteins like calmodulin. (correct answer)
  3. It buffers the intracellular pH to maintain optimal conditions for the ongoing enzymatic reactions.
  4. It is immediately chelated by ATP, which then carries the signal to the nucleus to alter transcription.
Explanation: The normally low cytosolic concentration of Ca²⁺ means that a sudden increase is a potent signal. These ions act as a second messenger by binding to calcium-binding proteins, such as calmodulin. The Ca²⁺-calmodulin complex can then activate other proteins, like kinases or phosphatases, to continue the cascade.

Question 11

A cell's response to a hormone must be temporary, requiring the signal to be terminated. Which mechanism is an essential, rapid 'off switch' for a signal cascade initiated by a G-protein coupled receptor?

  1. The hormone-receptor complex is permanently internalized and degraded by lysosomes.
  2. Target proteins that were phosphorylated are cleaved by proteases to stop their activity permanently.
  3. Second messenger molecules are actively transported from the cytoplasm to the nucleus for degradation.
  4. The G-protein's intrinsic GTPase activity hydrolyzes its bound GTP to GDP, rendering it inactive. (correct answer)
Explanation: The G-protein acts as a molecular switch. It is active when bound to GTP. Its own intrinsic enzymatic (GTPase) activity hydrolyzes GTP to GDP, which returns the G-protein to its inactive state. This is a critical and rapid step in terminating the signal.

Question 12

A researcher treats target cells with a chemical that is a non-competitive inhibitor of adenylyl cyclase. They then add a hormone that normally uses cAMP as a second messenger. What would be the expected result?

  1. The concentration of intracellular cAMP would not increase significantly, and the cellular response would be blocked. (correct answer)
  2. The hormone would be unable to bind to its cell-surface receptor due to conformational changes.
  3. The G-protein would fail to exchange GDP for GTP, preventing its activation by the receptor.
  4. The hormonal effects would be amplified because the cell would compensate by producing more G-proteins.
Explanation: Adenylyl cyclase is the enzyme responsible for synthesizing cAMP from ATP. Inhibiting this enzyme breaks the signalling chain. Even if the hormone binds its receptor and activates the G-protein, the inhibited adenylyl cyclase cannot produce the second messenger (cAMP), so the downstream cascade is blocked.

Question 13

An individual is under acute stress, triggering the 'fight or flight' response. What combination of signalling molecules and mechanisms originating from the adrenal gland would be expected for this immediate response?

  1. The adrenal medulla releases the amine hormone adrenaline, which binds to cell-surface receptors, activating a G-protein pathway. (correct answer)
  2. The adrenal cortex releases the steroid hormone cortisol, which binds to intracellular receptors to slowly alter gene expression.
  3. The adrenal medulla releases the steroid hormone aldosterone, which binds to membrane receptors to rapidly increase blood pressure.
  4. The adrenal cortex releases the peptide hormone adrenaline, which binds to intracellular receptors to mobilize glucose.
Explanation: The immediate 'fight or flight' response is mediated by adrenaline (epinephrine) from the adrenal medulla. Adrenaline is a catecholamine (an amine hormone derived from an amino acid) that acts like a peptide hormone, binding to cell-surface adrenergic receptors (which are GPCRs) to trigger a rapid, cAMP-mediated response.

Question 14

Which statement correctly distinguishes the role of a second messenger, such as Ca²⁺, from that of the initial hormone (the first messenger) in a typical peptide hormone pathway?

  1. The second messenger is responsible for terminating the signal by degrading the receptor, while the first messenger initiates it.
  2. The second messenger is typically a protein kinase that phosphorylates targets, while the first messenger is a steroid or peptide.
  3. The second messenger is a small, non-protein molecule that relays the signal within the cytoplasm, while the first messenger remains outside the cell. (correct answer)
  4. The second messenger binds directly to DNA to regulate gene expression, while the first messenger activates membrane-bound enzymes.
Explanation: The first messenger (hormone) binds to a receptor on the cell surface because it cannot enter the cell. This binding triggers the production or release of second messengers (small molecules or ions like cAMP or Ca²⁺) inside the cell, which then propagate the signal to intracellular targets.

Question 15

A newly discovered peptide hormone is found to regulate metabolic rate in adipose tissue. Which statement most accurately describes the initial steps of its mechanism of action?

  1. It diffuses through the cell membrane and binds to a cytoplasmic receptor, forming a complex that acts as a transcription factor.
  2. It binds to an extracellular domain of a transmembrane receptor, initiating a phosphorylation cascade involving second messengers. (correct answer)
  3. It is transported into the cell via a specific protein channel and directly activates mitochondrial enzymes to increase ATP production.
  4. It binds to a G-protein, which then directly translocates to the nucleus to alter gene expression without a second messenger.
Explanation: Peptide hormones are hydrophilic and cannot cross the plasma membrane. They bind to specific receptors on the cell surface, which triggers an intracellular signalling cascade, often involving phosphorylation and second messengers, to elicit a response.

Question 16

Which statement correctly compares a typical endocrine signal with a typical neural signal?

  1. Endocrine signals are transmitted more rapidly by action potentials and have a more localized effect on adjacent cells.
  2. Neural signals involve chemical messengers called hormones that travel long distances via the bloodstream to target organs.
  3. Endocrine signals are generally slower to be initiated, are more widespread in their distribution, and have a longer duration of action. (correct answer)
  4. Neural signals are typically mediated by steroid hormones released at a synapse, causing changes in gene transcription.
Explanation: The endocrine system relies on hormones traveling through the bloodstream, which is slower than nerve impulses. The hormones are broadcast throughout the body, affecting any cell with the appropriate receptor, and the effects are often prolonged. In contrast, neural signals are fast, targeted, and brief.

Question 17

Signal transduction cascades often involve a series of protein modifications. What are the respective roles of protein kinases and protein phosphatases in regulating these cascades?

  1. Kinases add phosphate groups to proteins, often activating them, while phosphatases remove these phosphate groups, often inactivating them. (correct answer)
  2. Kinases act as second messengers to amplify the signal, while phosphatases degrade them to terminate the signal.
  3. Kinases are transmembrane receptors that bind hormones, while phosphatases are intracellular enzymes that bind directly to DNA.
  4. Kinases synthesize second messengers like cAMP, while phosphatases are G-proteins that hydrolyze GTP to terminate the signal.
Explanation: This describes the fundamental, opposing roles of these two enzyme classes. Kinases catalyze phosphorylation (adding phosphate groups), which typically acts as an 'on' switch. Phosphatases catalyze dephosphorylation (removing phosphate groups), acting as an 'off' switch, thereby allowing the system to be reset.

Question 18

Based on the principles of chemical signalling, what can be deduced about a hormone that is transported in the blood bound to a carrier protein and has a half-life of several hours?

  1. It is a peptide hormone that binds to a transmembrane G-protein coupled receptor.
  2. It is a hydrophilic molecule that requires facilitated diffusion to enter its target cell.
  3. It is a neurotransmitter that acts locally at a synapse before entering general circulation for removal.
  4. It is a hydrophobic molecule, such as a steroid, that likely acts by altering gene expression. (correct answer)
Explanation: Hydrophobic hormones (steroids, thyroid hormones) are not soluble in aqueous blood and require carrier proteins for transport. This protection from enzymes and filtration by the kidney gives them a long half-life. Their lipid nature allows them to cross cell membranes to act on intracellular receptors, typically modifying gene expression.

Question 19

Cortisol is a steroid hormone that helps regulate the immune response. Which feature is essential for its primary mechanism of action?

  1. Its hydrophilic nature, allowing it to dissolve easily in the blood plasma without a carrier protein.
  2. Its ability to bind to cell-surface receptors and trigger a rapid, non-genomic phosphorylation cascade.
  3. Its lipid-soluble nature, allowing it to diffuse across the cell membrane and bind to an intracellular receptor. (correct answer)
  4. Its structure allows it to act as a direct competitive inhibitor for enzymes in key metabolic pathways.
Explanation: Steroid hormones are hydrophobic (lipid-soluble). This property allows them to pass through the plasma membrane and bind to receptors located in the cytoplasm or nucleus. The resulting hormone-receptor complex then acts as a transcription factor, directly altering gene expression.

Question 20

A liver cell has receptors for both insulin (a peptide hormone) and cortisol (a steroid hormone). How will their initial signal reception and transduction mechanisms differ?

  1. Insulin will bind to a cell-surface receptor, while cortisol will diffuse into the cell to bind a cytoplasmic receptor. (correct answer)
  2. Both will bind to cell-surface receptors, but insulin will use a G-protein while cortisol will use a tyrosine kinase.
  3. Both will diffuse into the cell, but insulin will bind to a cytoplasmic receptor while cortisol will bind to a nuclear receptor.
  4. Cortisol will bind to a cell-surface receptor to trigger a fast response, while insulin will enter the nucleus for a slow response.
Explanation: This correctly identifies the fundamental difference. Insulin, a peptide, is hydrophilic and binds to a receptor tyrosine kinase on the cell surface. Cortisol, a steroid, is hydrophobic and can pass through the plasma membrane to bind to its receptor inside the cell (in the cytoplasm), which then moves to the nucleus.