Question 1
A receptor protein binds acetylcholine but not other small molecules present in extracellular fluid. What property of the receptor accounts for this specificity?
A.
A permanent covalent bond formed between acetylcholine and the receptor
B.
A hydrophobic core that allows all signalling chemicals to enter the receptor
C.
A catalytic site that converts acetylcholine into an inactive product
D.
A binding site with shape and chemical properties complementary to acetylcholine
Question 2
A small protein is secreted by an immune cell during inflammation and acts mainly on nearby cells with plasma membrane receptors. What functional category does this signalling chemical belong to?
A.
Steroid hormone
B.
Cytokine
C.
Neurotransmitter
D.
Calcium ion
Question 3
What is the correct chemical classification of insulin, epinephrine and testosterone?
A.
Insulin is an amine hormone; epinephrine is a steroid hormone; testosterone is a peptide hormone
B.
Insulin is a steroid hormone; epinephrine is a peptide hormone; testosterone is an amine hormone
C.
Insulin is a gaseous signal; epinephrine is a steroid hormone; testosterone is a peptide hormone
D.
Insulin is a peptide hormone; epinephrine is an amine hormone; testosterone is a steroid hormone
Question 4
A signalling molecule is released into the blood and only cells in distant organs with the matching receptor respond. What best explains the specificity of the response?
A.
The blood carries the signalling molecule only to one cell type
B.
All cells exposed to a hormone produce the same response
C.
Distant signalling molecules always diffuse directly across synaptic gaps
D.
Only target cells have receptors able to bind the signalling molecule
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 5
Acetylcholine binds to receptors in the postsynaptic membrane at a neuromuscular junction. What immediate effect does this have on the receptor?
A.
The receptor phosphorylates tyrosine residues and inserts glucose transporters into the membrane
B.
An ion channel in the receptor opens, allowing positively charged ions to enter the cell
C.
The receptor converts ATP to cyclic AMP on the cytoplasmic side of the membrane
D.
The receptor enters the nucleus and binds to specific DNA sequences
Question 6
Acetylcholine binds to acetylcholine receptors but does not bind effectively to many other proteins in the membrane.
Define the term ligand in cell signalling.
[1]
Explain why a receptor responds to one signalling chemical but not to every small molecule around the cell.
[2]
Question 7
The graph shows changes in a culture of Vibrio fischeri as cell density increases. What explains the onset of bioluminescence at high cell density?
A.
Each bacterium counts neighbouring cells by direct contact and then starts translation of autoinducer
B.
Low oxygen at high density causes all genes involved in light production to be permanently repressed
C.
Autoinducer accumulates and the autoinducer-receptor complex promotes transcription of luciferase genes
D.
Luciferase diffuses out of each cell and directly activates receptors in neighbouring bacteria
Question 8
A hydrophilic peptide hormone causes a response in a target cell without entering the cytoplasm. What receptor property is most consistent with this response?
A.
It is a transmembrane protein with an extracellular ligand-binding region
B.
It is a soluble nuclear receptor that binds directly to a DNA sequence before hormone binding
C.
It lacks hydrophobic amino acids in regions contacting the phospholipid bilayer
D.
It is transported in vesicles from the nucleus to the extracellular fluid
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 9
What is a second messenger in a signal transduction pathway?
A.
A receptor protein that recognizes several unrelated signalling molecules at once
B.
A small intracellular molecule produced or released after receptor activation that relays the signal
C.
An enzyme that removes the ligand before any intracellular response can begin
D.
A ligand secreted by a source cell that binds first to the receptor outside the target cell
Question 10
A ligand binds to a G protein-coupled receptor. What change activates the associated G protein?
A.
The beta and gamma subunits are phosphorylated by the receptor before ligand binding
B.
GTP leaves the alpha subunit and GDP binds in its place
C.
Cyclic AMP binds to the extracellular domain of the receptor
D.
GDP leaves the alpha subunit and GTP binds in its place
Question 11
Insulin binds to its receptor on a muscle cell. What sequence best describes the receptor mechanism leading to increased glucose uptake?
A.
Insulin opens an ion channel; enters; depolarization inserts glucose transporters by exocytosis
B.
Insulin activates a G protein; adenylyl cyclase makes cyclic AMP; cyclic AMP enters the blood with glucose
C.
Insulin crosses the membrane; the insulin-receptor complex binds DNA; glucose transporter genes are immediately translated
D.
Insulin binds extracellularly; tyrosine residues are phosphorylated; vesicles with glucose transporters move to the plasma membrane
Question 12
What is an example of negative feedback in chemical signalling?
A.
Increased testosterone inhibits GnRH release from the hypothalamus and reduces LH release from the anterior pituitary
B.
Acetylcholine opens a postsynaptic ion channel, causing positive ions to enter and depolarize the membrane
C.
Oestradiol near ovulation stimulates GnRH release, promoting further reproductive hormone signalling
D.
Autoinducer accumulation in Vibrio fischeri promotes transcription of luciferase genes at high cell density
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 13
Animal cells use several functional categories of signalling chemicals.
Identify the category of signalling chemical that is secreted by endocrine cells and transported in the blood to target cells.
[1]
Distinguish between neurotransmitters and cytokines as signalling chemicals.
[2]
State one role of as an intracellular signal in animals.
[1]
Question 14
Hormones and neurotransmitters are chemically diverse.
State two chemical groups of hormones, giving one example of each.
[1]
Explain one reason why different chemical types of signalling molecules use different receptor locations.
[2]
Question 15
A hormone and a neurotransmitter both act by binding to specific receptors on target cells.
Compare the distances over which hormones and neurotransmitters usually act.
[2]
Explain why a blood-borne hormone does not cause every cell in the body to respond.
[1]
Question 16
Binding of a signalling chemical to a receptor is usually the first event in a cellular response.
Define signal transduction pathway.
[1]
Explain how ligand binding to a transmembrane receptor can initiate a response inside the cell.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 17
A receptor protein from a postsynaptic membrane was purified and exposed to acetylcholine and to three structurally related molecules. Binding to the receptor and the proportion of receptors showing a conformational change were measured.
Ligand | Relative binding / % | Conformational change / % |
|---|---|---|
Acetylcholine | 100 | 95 |
Ligand 1 | 42 | 18 |
Ligand 2 | 23 | 9 |
Ligand 3 | 5 | 1 |
Identify the evidence that the receptor is specific for acetylcholine.
[1]
Describe what the data suggest about the receptor binding site.
[2]
Explain why this receptor is not functioning as an enzyme in this investigation.
[1]
Question 18
Several signalling chemicals were compared for chemical group, solubility and receptor location in target cells.
Molecule | Chemical group | Water solubility | Crosses membrane? | Receptor location |
|---|---|---|---|---|
Insulin | Protein/peptide hormone | Hydrophilic | No | Plasma membrane |
Epinephrine | Amine hormone | Hydrophilic | No | Plasma membrane |
Testosterone | Steroid hormone | Hydrophobic | Yes | Intracellular |
Nitrous oxide | Gaseous signalling molecule | Low water solubility | Yes | Intracellular |
Classify insulin, epinephrine, testosterone and nitrous oxide by chemical type.
[2]
Explain how chemical diversity allows signalling chemicals to use different routes to their receptors.
[2]
Question 19
The diagram represents part of the epinephrine signalling pathway in a liver cell. What molecule is represented by X?
A.
Cyclic AMP
B.
Tyrosine kinase
C.
Insulin
D.
Glycogen
Question 20
A culture of Vibrio fischeri was grown in a flask. The concentration of autoinducer and the light emitted by the culture were measured as bacterial cell density increased.
Deduce the relationship between bacterial cell density and bioluminescence in this culture.
[1]
Explain how quorum sensing causes light production in V. fischeri.
[3]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 21
Receptors for signalling chemicals may be located in the plasma membrane, cytoplasm or nucleus.
Distinguish between transmembrane receptors and intracellular receptors.
[2]
Explain how the distribution of hydrophobic and hydrophilic amino acids allows a transmembrane receptor to be positioned in a membrane.
[2]
Question 22
The diagram shows a synapse with acetylcholine receptors in the postsynaptic membrane.
State the type of receptor that binds acetylcholine in the postsynaptic membrane.
[1]
Explain how acetylcholine binding can change the membrane potential of the postsynaptic cell.
[3]
Question 23
Many human receptors are G protein-coupled receptors.
Outline how ligand binding activates a G protein-coupled receptor pathway.
[3]
State what the activated G protein does next in the cell.
[1]
Question 24
Insulin is a protein hormone that increases glucose uptake in some target cells.
Explain why the insulin receptor is located in the plasma membrane rather than in the cytoplasm.
[1]
Outline how insulin binding leads to increased glucose uptake by the target cell.
[3]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 25
Cultures of the marine bacterium Vibrio fischeri were grown from low cell density. Autoinducer concentration, transcription of genes coding for luciferase, and bioluminescence were monitored.
Describe the relationship between autoinducer concentration and bioluminescence.
[2]
Explain how quorum sensing causes the increase in bioluminescence.
[2]
Suggest why isolated free-living V. fischeri cells would produce little visible light.
[1]
Question 26
Four animal signalling chemicals were compared for their source, route of movement, distance of action and usual speed of response.
Signal | Source | Route of movement | Distance of action | Usual response time | Site of action |
|---|---|---|---|---|---|
Insulin | Endocrine cells | In blood | Distant target cells | Minutes to hours | Plasma membrane of target cell |
Acetylcholine | Neurone terminals | Across synaptic cleft | Adjacent postsynaptic cell | Milliseconds | Plasma membrane of postsynaptic cell |
Cytokine | Immune cells | Through tissue fluid | Nearby cells | Minutes to hours | Plasma membrane of target cell |
Calcium ion | Intracellular stores | Released into cytoplasm | Within the same cell | Seconds | Cytoplasm |
Identify the signal that is most likely to be a hormone.
[1]
Compare the expected range of action of a hormone and a neurotransmitter.
[2]
Explain why the cytokine and calcium ion in the table are expected to act in different cellular locations.
[2]
Question 27
Two receptor proteins were analysed. Receptor X is located in the plasma membrane and receptor Y is located in the cytoplasm. A hydropathy plot and a simplified cell diagram are shown.
Identify which receptor is a transmembrane receptor.
[1]
Explain the amino acid distribution expected in receptor X.
[2]
Suggest which receptor location would be used by a peptide hormone.
[1]
Question 28
Acetylcholine was applied briefly to a postsynaptic membrane containing acetylcholine receptors. Membrane potential and ion movement were recorded.
Phase | Membrane potential with ACh / mV | influx with ACh / arbitrary units | Membrane potential with ACh + antagonist / mV | influx with ACh + antagonist / arbitrary units |
|---|---|---|---|---|
Resting before ACh | -70 | 0.2 | -70 | 0.2 |
During brief ACh exposure | -55 | 4.6 | -69 | 0.3 |
20 s after ACh removed | -70 | 0.2 | -70 | 0.2 |
State the effect of acetylcholine on membrane potential.
[1]
Explain how binding of acetylcholine causes this change.
[2]
Suggest the effect of adding a competitive antagonist of the acetylcholine receptor before acetylcholine is applied.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 29
Cultured muscle cells were exposed to insulin. In one treatment, a tyrosine kinase inhibitor was added before insulin. Tyrosine phosphorylation, number of glucose transporters in the plasma membrane and glucose uptake were measured.
State the effect of insulin on the number of glucose transporters in the plasma membrane.
[1]
Explain the effect of the tyrosine kinase inhibitor.
[2]
Suggest why insulin binds to a receptor in the plasma membrane rather than to an intracellular receptor.
[1]
Question 30
Epinephrine, also called adrenaline, can stimulate glycogen breakdown in liver cells.
Outline the sequence from epinephrine binding to production of cyclic AMP.
[3]
Suggest how this signalling pathway can amplify the original hormone signal.
[1]
Question 31
Steroid hormones can affect target cells and can also participate in feedback regulation of signalling pathways.
State the target cell type or target tissue for the effects of oestradiol and progesterone specified in this topic.
[2]
Distinguish positive feedback from negative feedback in cell signalling, using one reproductive hormone example for each.
[2]
Question 32
Two signalling chemicals were applied separately to cultured animal cells. Signal A remained outside the cell and caused a rapid rise in a second messenger. Signal B entered the cell and later increased transcription of target genes.
Describe two differences between the responses to signal A and signal B.
[2]
Explain why signal A is likely to use a transmembrane receptor.
[2]
Suggest why the response to signal B is slower.
[1]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 33
A G protein-coupled receptor in the plasma membrane was studied before and after addition of its ligand. Binding of GDP or GTP to the alpha subunit and activity of an effector enzyme were measured.
Condition | GDP bound to subunit / % | GTP bound to subunit / % | Effector activity / a.u. |
|---|---|---|---|
Before ligand addition | 92 | 8 | 14 |
After ligand addition | 18 | 82 | 63 |
Identify the nucleotide associated with the inactive G protein.
[1]
Describe the effect of ligand binding on the G protein and effector enzyme.
[2]
Explain how the receptor conveys a signal into the cell without the ligand entering the cytoplasm.
[1]
Question 34
Liver cells were treated with epinephrine. Some cells were also treated with a drug that prevents activation of G proteins. Concentrations of cyclic AMP and activity of a protein kinase were measured.
Treatment | Cyclic AMP concentration / pmol mg protein | Protein kinase activity / arbitrary units |
|---|---|---|
No epinephrine | 1.0 | 2.0 |
Epinephrine | 8.0 | 16.0 |
Epinephrine + G-protein inhibitor | 1.1 | 2.2 |
Identify the enzyme that produces cyclic AMP in the epinephrine pathway.
[1]
Describe the effect of the G-protein inhibitor on the response to epinephrine.
[2]
Explain how the epinephrine pathway can amplify a signal.
[2]
Question 35
Steroid hormones were added to two types of target cell: hypothalamic cells that secrete gonadotropin-releasing hormone and endometrial cells. Target-gene transcription was measured over time.
Identify the target cell type for each hormone shown.
[2]
Explain why the response to these steroid hormones is delayed rather than immediate.
[2]
Suggest the effect of adding a receptor antagonist for the steroid hormone.
[1]
Question 36
A cell is exposed to many small molecules in extracellular fluid, but only one of them acts as a signalling chemical for this cell. The diagram shows a receptor protein in the plasma membrane and three possible ligands.
I.
Define the term ligand in chemical signalling.
[1]
II.
Explain why only some extracellular molecules bind to the receptor shown.
[2]
Compare the role of a receptor with the role of an enzyme in relation to the molecule that binds to it.
[2]
Discuss how receptor specificity contributes to communication between cells.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 37
Animal cells use several functional categories of signalling chemicals. The same tissue may receive hormones, neurotransmitters and cytokines, while also using as an intracellular signal.
I.
State one example of a hormone and one example of a neurotransmitter.
[1]
II.
Distinguish between hormones and neurotransmitters in terms of transport and typical effect.
[2]
Explain why cytokines usually bind to transmembrane receptors.
[2]
Discuss how differs from the other signalling chemicals listed in the stem.
[2]
Question 38
A drug is designed to slow the removal of a signalling molecule after it is released. The effect of the drug differs depending on whether the signalling molecule is a neurotransmitter at a synapse or a hormone in the blood.
I.
Identify which of the two pathways in the diagram has the more localized effect.
[1]
II.
Give one reason for this localization.
[1]
Explain why hormones can have distant effects but still act specifically.
[3]
Evaluate the likely effect of slowing signal removal at a synapse compared with slowing removal of a circulating hormone.
[2]
Question 39
Two reproductive signalling pathways were modelled. In model A, increasing oestradiol affects gonadotropin-releasing hormone secretion near ovulation. In model B, increasing testosterone affects gonadotropin-releasing hormone and luteinizing hormone secretion.
Distinguish the feedback type shown in model A from the feedback type shown in model B.
[2]
Outline one general difference between positive and negative feedback in cell signalling pathways.
[1]
Evaluate the predicted effect of blocking testosterone receptors in model B.
[2]
Question 40
Cultures of the marine bacterium Vibrio fischeri were grown at different cell densities. Autoinducer concentration, transcription of luciferase genes and light output were measured.
I.
Deduce the cell-density range in which quorum sensing is activated.
[1]
II.
Explain why light output remains low at low bacterial density.
[2]
Explain how quorum sensing leads to bioluminescence in V. fischeri.
[3]
Evaluate the advantage of linking bioluminescence to population density rather than producing light continuously.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 41
A pharmaceutical researcher is comparing four signalling chemicals: insulin, testosterone, epinephrine and glutamate. Their chemical properties affect how they are transported, how they are detected and how quickly their effects can be regulated.
Chemical | Structure | Solubility | Receptor location | Transport / route | Typical effect time |
|---|---|---|---|---|---|
Insulin | large amino-acid chain | hydrophilic | cell-surface transmembrane receptor | blood / plasma | minutes to hours |
Testosterone | cholesterol-derived ring molecule | lipid-soluble | intracellular receptor (cytoplasm / nucleus) | blood / plasma; carrier-bound | hours to days |
Epinephrine | small amine-containing molecule | hydrophilic | cell-surface transmembrane receptor | blood / plasma | seconds to minutes |
Glutamate | small amino acid | hydrophilic | postsynaptic transmembrane receptor | synaptic cleft | milliseconds to seconds |
I.
Classify insulin, testosterone and epinephrine into hormone chemical groups.
[2]
II.
State the neurotransmitter class represented by glutamate.
[1]
Explain how solubility affects whether a signalling chemical uses a transmembrane or intracellular receptor.
[3]
Discuss one advantage of chemical diversity among hormones and neurotransmitters.
[2]
Question 42
Two receptor proteins are being compared. Receptor X is embedded in the plasma membrane and binds a water-soluble peptide signal. Receptor Y is found in the cytoplasm and binds a lipid-soluble steroid signal.
I.
Identify which receptor is transmembrane and which is intracellular.
[1]
II.
Explain why the peptide signal binds to receptor X rather than receptor Y.
[2]
Compare the distribution of hydrophobic and hydrophilic amino acids in receptor X and receptor Y.
[3]
Discuss how receptor location affects the first step of signal transduction for each receptor.
[2]
Question 43
A cell surface receptor and an intracellular receptor can both produce a cellular response after binding a signalling chemical, but the sequence of events differs.
I.
State what is meant by signal transduction.
[1]
II.
State why a second messenger is useful in some signal transduction pathways.
[1]
Explain how binding of a ligand to a transmembrane receptor initiates a cellular response.
[3]
Compare the likely timing of responses initiated by transmembrane receptors and intracellular steroid receptors.
[2]
Question 44
Acetylcholine receptors in a postsynaptic membrane are ligand-gated ion channels. The graph shows the membrane potential of a postsynaptic cell before and after acetylcholine is released.
I.
Identify the change in membrane potential after acetylcholine release.
[1]
II.
State the ion movement that directly causes this change.
[1]
III.
State why the receptor is described as ligand-gated.
[1]
Explain how acetylcholine binding changes the voltage across the postsynaptic membrane.
[3]
Discuss why rapid removal or breakdown of acetylcholine is important after receptor activation.
[2]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
Question 45
Many human receptors are G protein-coupled receptors. A model of one such receptor and its associated G protein is shown before and after ligand binding.
I.
Identify the nucleotide bound to the inactive alpha subunit.
[1]
II.
Identify the nucleotide that binds when the G protein is activated.
[1]
Explain how a GPCR conveys a signal from outside the cell to an intracellular effector.
[3]
Discuss why many different GPCRs can be useful in humans.
[2]
Question 46
Insulin receptors are transmembrane receptors with tyrosine kinase activity. In muscle and adipose cells, insulin signalling increases the number of glucose transporters in the plasma membrane.
I.
Explain why insulin does not normally bind to an intracellular receptor.
[1]
II.
State what phosphorylation means.
[1]
Explain how insulin binding leads to increased glucose uptake by the target cell.
[4]
Discuss why increasing transporter number is an effective way to change glucose uptake rapidly.
[1]
Question 47
Liver cells were exposed to epinephrine. In one treatment, an inhibitor of adenylyl cyclase was added before epinephrine. Concentrations of cyclic AMP and activity of glycogen-breakdown enzymes were measured.
I.
Identify the second messenger in the epinephrine pathway.
[1]
II.
State the role of adenylyl cyclase in this pathway.
[1]
III.
Deduce the effect of the inhibitor from the results.
[1]
Explain the mechanism by which epinephrine activates glycogen breakdown in liver cells.
[3]
Evaluate the importance of amplification in the epinephrine signalling pathway.
[2]
Question 48
Steroid hormones can affect target cells by activating intracellular receptors. Oestradiol, progesterone and testosterone each bind specific receptors and alter gene expression in responsive cells.
I.
State why steroid hormones can enter target cells.
[1]
II.
Explain how an activated steroid hormone receptor promotes gene transcription.
[2]
Compare the specified target-cell effects of oestradiol and progesterone.
[2]
Discuss how steroid hormone signalling can be involved in both positive and negative feedback.
[3]
Build a Practice Exam — Biology HL
Test your knowledge with a custom paper containing questions from selected topics.
The Ultimate All-in-One
IB Platform
All content on this website has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate and IB are registered trademarks owned by the International Baccalaureate Organization.