Question 1
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanWhich signalling chemical binds to a receptor in the cytoplasm or nucleus of its target cell?
- Insulin
- Epinephrine (adrenaline)
- Acetylcholine
- Testosterone
Show mark scheme for question 1
Answer: D [1]
Question 2
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanWhat acts as the second messenger when epinephrine binds to its receptor on a liver cell?
- GTP
- Cyclic AMP
- Phosphorylated tyrosine
- Calcium ions released from the blood
Show mark scheme for question 2
Answer: B [1]
Question 3
Paper 1A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanWhich is an example of positive feedback in a cell signalling pathway?
- Rising oestradiol increases GnRH secretion, leading to more oestradiol secretion
- Insulin lowers blood glucose, so less insulin is secreted
- A G protein hydrolyses GTP to GDP and becomes inactive
- A steroid hormone binds an intracellular receptor that promotes transcription
Show mark scheme for question 3
Answer: A [1]
Question 4
Paper 1B style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanVibrio fischeri was grown in a flask of liquid medium. Population density and light output were measured every 2 hours. The data are for practice. (a) Describe the relationship between population density and light output. [2] (b) Calculate the percentage increase in light output between 6 h and 10 h. [1] (c) Explain the results in terms of quorum sensing. [3]
| Time / h | Population density / 10⁷ cells cm⁻³ | Light output / arbitrary units |
|---|---|---|
| 0 | 0.1 | 1 |
| 2 | 0.4 | 1 |
| 4 | 1.6 | 2 |
| 6 | 6.0 | 50 |
| 8 | 18.0 | 450 |
| 10 | 30.0 | 900 |
Show mark scheme for question 4
- (a) little or no light at low population density / up to 4 h [1]
- (a) light output rises steeply once density exceeds about 1.6–6 × 10⁷ cells cm⁻³ / increase is not proportional to density [1]
- (a) positive correlation between density and light output overall [1]
- (a) max 2
- (b) (900 − 50) ÷ 50 × 100 = 1700% [1]
- (c) bacteria release a signalling chemical / autoinducer [1]
- (c) its concentration rises as population density rises [1]
- (c) above a threshold concentration it binds to receptors (in the bacteria) [1]
- (c) activated receptor promotes transcription of genes for bioluminescence / luciferase [1]
- (c) positive feedback: more autoinducer is made once activated, so light output rises steeply [1]
- (c) max 3
Question 5
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanDistinguish between transmembrane receptors and intracellular receptors.
Show mark scheme for question 5
- transmembrane in plasma membrane, intracellular in cytoplasm / nucleus [1]
- transmembrane has hydrophobic amino acids in the region within the membrane / intracellular has hydrophilic amino acids on its surface / no hydrophobic membrane region [1]
- ligand of transmembrane receptor remains outside the cell, ligand of intracellular receptor enters the cell [1]
- transmembrane ligands are hydrophilic / proteins / amines, intracellular ligands are hydrophobic / steroids [1]
- intracellular receptors (when activated) bind DNA / affect gene expression directly [1]
- max 3
- Each mark needs both sides of the contrast. Accept a table.
Question 6
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanCompare and contrast hormones and neurotransmitters as signalling chemicals.
Show mark scheme for question 6
- both bind to specific receptors on/in target cells [1]
- both trigger a response / signal transduction in the target cell [1]
- hormones secreted by endocrine glands, neurotransmitters released by neurons [1]
- hormones transported in the blood, neurotransmitters diffuse across a synaptic gap / cleft [1]
- hormones have distant / widespread effects, neurotransmitters localized effects / one cell [1]
- hormone effects slower and longer lasting, neurotransmitter effects rapid and brief [1]
- max 4
- Award at least one mark for a similarity for full marks.
Question 7
Paper 2A style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanOutline how the binding of insulin to its receptor increases the uptake of glucose by a target cell.
Show mark scheme for question 7
- insulin binds to a (transmembrane) receptor in the plasma membrane / insulin does not enter the cell [1]
- receptor has tyrosine kinase activity / tyrosine (inside the cell) is phosphorylated [1]
- sequence of reactions / signal transduction follows [1]
- vesicles containing glucose transporters move to / fuse with the plasma membrane [1]
- more glucose enters by facilitated diffusion [1]
- max 3
Question 8
Paper 2B style
HL only (what this means)
HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels meanExplain how signalling chemicals that bind to receptors in the plasma membrane cause responses inside a cell. Use the acetylcholine receptor and the epinephrine (adrenaline) receptor as examples.
Show mark scheme for question 8
- ligand binds to a specific binding site on the receptor (outside the cell) [1]
- binding causes a conformational change in the receptor [1]
- starts a signal transduction pathway / sequence of responses inside the cell [1]
- acetylcholine receptor contains an ion channel that opens when acetylcholine binds [1]
- positively charged ions / Na⁺ diffuse into the cell [1]
- membrane potential changes / membrane depolarized / may trigger an action potential or muscle contraction [1]
- epinephrine receptor is a G protein-coupled receptor [1]
- G protein activated / binds GTP (in place of GDP) [1]
- G protein activates adenylyl cyclase [1]
- ATP converted to cAMP [1]
- cAMP is the second messenger / activates protein kinase [1]
- cascade amplifies the signal / leads to glycogen breakdown (in liver cells) [1]
- epinephrine does not enter the cell [1]
- max 7