IB Biology HL C2.1 Chemical Signalling Hl Only Questions
Practise IB Biology HL C2.1 by comparing ligands, receptors, hormones, quorum sensing and intracellular signalling pathways.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- Identify receptor proteins as specific ligand-binding sites and explain signalling specificity.
- Explain quorum sensing through autoinducer thresholds and coordinated bacterial behaviour.
- Compare animal signalling categories and local or distant communication, using leptin.
- Classify hormones and distinguish peptide versus steroid receptor routes.
- Compare transmembrane and intracellular receptor pathways for hydrophilic and steroid ligands.
- Trace signal transduction through second messengers, gene-regulatory proteins and phosphorylation cascades.
- Trace epinephrine GPCR signalling through G protein, adenylyl cyclase and cyclic AMP.
- Explain intracellular steroid or thyroxine-like receptor complexes regulating transcription.
- Explain negative feedback as an opposite response returning a regulated variable toward prior levels.
Covered syllabus points
C2.1.1 (HL)—Receptors as proteinsC2.1.2 (HL)—Quorum sensing in bacteriaC2.1.3 (HL)—Functional categories in animalsC2.1.4 (HL)—Chemical diversityC2.1.5 (HL)—Localized vs. distant effectsC2.1.6 (HL)—Transmembrane vs. intracellular receptorsC2.1.7 (HL)—Signal transduction pathwaysC2.1.8 (HL)—Neurotransmitter receptors and membrane potentialC2.1.9 (HL)—G protein-coupled receptorsC2.1.10 (HL)—Epinephrine (adrenaline) mechanismC2.1.11 (HL)—Tyrosine kinase receptorsC2.1.12 (HL)—Intracellular receptorsC2.1.13 (HL)—Effects of oestradiol and progesteroneC2.1.14 (HL)—Regulation by feedback
Question 1
[Maximum number: 4]
The complementarity of shapes and chemical properties allows molecules to bind to each other.
Describe, with examples, the types of molecule within cell-to-cell signalling systems that are complementary to each other.
a. signalling chemicals/ligands bind to receptors;
b. reference to specificity / the shape (and chemical properties) of the ligand-binding site match those of the ligand;
c. receptors can be in (either) the plasma membrane / intracellular / in the cytoplasm / or nucleus
OR
ligand can bind to transmembrane receptors/receptors in the plasma membrane or intracellular receptors;
d. only cells with a receptor to a signalling chemical will respond;
e. reference to signal transduction (initiated by signalling chemical-receptor binding);
f. example of signalling chemical;
Do not accept the role of glycoproteins in cell-cell recognition or ABO glycoproteins.
For b: do not accept "complementary" as this is part of the stem question.
For e. OWTTE
For e. the reference may include the pathway followed by a given example of a signalling chemical.
Appropriate example for (f):
- Neurotransmitters/named neurotransmitter
- any named hormone
- Cytokine
- Calcium ions
Question 2
[Maximum number: 2]
State, giving one specific example, how individual bacteria change their characteristics when they form aggregates.
F2. (a) a. example;
b. change;
e.g.:
a. Vibrio fischeri;
b. emit light when part of high density population/high concentration of regulatory substance;
Marking guidance:
Accept other verifiable example.
Question 3
[Maximum number: 1]
What releases leptin?
A
Thyroid gland
B
Hypothalamus
C
Pineal gland
D
Adipose tissue
D
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