Explain cell-surface signalling and recognition
Specific ligands travel from secreting cells to target cells and bind to matching surface receptors to produce a response.
AS Level · Cambridge International Biology 9700, 2028–2030. These lessons explain membrane transport and investigation reasoning. Written practice is self-checked; it does not demonstrate supervised practical competence or replace teacher-reviewed assessment.
Before you begin
- Relate phospholipid and protein structure to their roles, and distinguish a concentration gradient from the direction of net movement.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What binds to a specific cell-surface receptor?
What you will learn
- Relate receptors and cell-surface antigens to signalling and recognition
- Outline ligand secretion, transport, receptor binding and a specific target-cell response
Recognition depends on surface molecules
Glycoproteins and glycolipids can carry carbohydrate chains that act as cell-surface markers or antigens. Differences among these molecules can help cells or the immune system distinguish cell surfaces.
A receptor is a membrane protein with a binding site for a particular signalling molecule, or ligand. Specific binding depends on complementary interactions; not every ligand binds every receptor.
Signals travel between cells
A signalling cell secretes a specific ligand. The ligand is transported to a target cell and binds to a complementary receptor on its surface. This binding leads to a specific response in the target cell.
Keep the stages in order: secretion, transport, binding, response. This syllabus outcome asks for the main stages; it does not require a detailed intracellular signalling cascade.
Pause and explain
What is the correct main order of cell-surface signalling?
Worked example
A hormone is released by one cell, travels in blood and binds to a receptor on a target cell. Outline the signalling sequence.
Show the worked solution
- The signalling cell secretes a ligand.
- It is transported to a target cell and binds to its matching surface receptor.
- Receptor binding leads to a specific response.
Answer The signalling cell secretes the hormone as a ligand. It is transported to the target cell, binds to a complementary cell-surface receptor and triggers a specific response in that target cell.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Outline the four main stages in a signal from one cell to a target cell.
Give me a hint
Begin with release of the signal and finish with the target response.
Compare my reasoning
- The signalling cell secretes a ligand.
- The ligand travels, binds to its surface receptor and leads to a specific response.
A signalling cell secretes a specific ligand. The ligand is transported to a target cell, binds to a complementary cell-surface receptor and leads to a specific response in that target cell.
Look for these in your work
- All four stages in order
- Specific target response stated
A ligand reaches a cell but the cell lacks the matching receptor. Predict the response using the syllabus model.
Give me a hint
Relate response to specific receptor binding.
Compare my reasoning
- The ligand cannot bind to its matching surface receptor.
- The stated signalling pathway is not initiated in that cell.
The cell is not the matching target in this model: without a complementary receptor the ligand does not bind, so the specific response described by this pathway is not initiated.
Look for these in your work
- Receptor specificity used
- Response conclusion appropriately limited
A cell’s surface carbohydrate chain is attached to a lipid. Name the structure and one way it may contribute to cell interactions.
Give me a hint
Use the carbohydrate-bearing membrane component.
Compare my reasoning
- A carbohydrate chain on a lipid is a glycolipid.
- Its outer chain can act as a recognition marker.
It is a glycolipid. Its outer carbohydrate chain can act as a cell-surface marker and contribute to cell recognition.
Look for these in your work
- Glycolipid named
- Recognition role stated
Common mistakes
- Calling a receptor a ligand
- Saying every cell responds to every signal
- Skipping transport or binding when outlining the sequence
What can you explain now?
What binds to a specific cell-surface receptor?
Compare with the explanation
A matching ligand
A ligand is the signalling molecule recognised by the receptor.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
What are ligand and receptor, and what sequence links secretion to a target-cell response?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.