AP Biology: Cell Communication Practice Questions
Test yourself on AP Biology: Cell Communication with 12 original AP Exams practice questions. Pick an answer to see instant feedback and a full explanation.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
advertisement
Answer the questions below — you get instant feedback and a full explanation for each.
1. A peptide hormone binds to a receptor on the outside of a target cell. Why does the hormone usually not enter the cell directly?
Explanation. Peptide hormones are generally hydrophilic or polar, so they do not easily cross the hydrophobic lipid bilayer. They bind cell-surface receptors and trigger intracellular signal transduction. Small nonpolar steroid hormones are more likely to diffuse through the membrane and bind intracellular receptors.
2. In a signal transduction pathway, ligand binding changes the shape of a receptor. What is the most direct result of that conformational change?
Explanation. Binding of a signaling molecule often changes receptor shape, activating the receptor or allowing it to interact with another protein. That begins the intracellular response pathway. Cell division may be a later response in some pathways, but it is not the immediate direct result.
3. A G protein-coupled receptor (GPCR) is activated by a ligand. Which event commonly occurs next?
Explanation. Activated GPCRs commonly cause an associated G protein to release GDP and bind GTP. The active G protein subunit can then regulate an enzyme or ion channel. DNA cutting, ribosome movement, and glucose synthesis are not standard GPCR activation steps.
4. In many signaling pathways, cAMP is described as a second messenger. What does this mean?
Explanation. A second messenger is an intracellular molecule that relays and often amplifies a signal after an extracellular ligand binds a receptor. cAMP is made from ATP by adenylyl cyclase and can activate protein kinase A. The ligand itself is the first messenger.
5. A mutation prevents a receptor tyrosine kinase (RTK) from dimerizing after ligand binding. Which outcome is most likely?
Explanation. RTKs commonly signal when ligand binding promotes receptor dimerization. The receptor tails then cross-phosphorylate tyrosines, creating docking sites for downstream proteins. If dimerization is blocked, activation and downstream signaling are usually reduced.
6. Which statement best explains signal amplification in a phosphorylation cascade?
Explanation. In a cascade, one activated kinase may phosphorylate many substrate proteins, and each of those can affect many more proteins. This branching increases the size of the response from a small initial signal. Cascades do not require receptor movement into the nucleus.
7. A drug inhibits protein phosphatases in a cell. How would this most directly affect pathways controlled by phosphorylation?
Explanation. Protein phosphatases remove phosphate groups from proteins, often reversing the effects of kinases. If phosphatases are inhibited, phosphorylated states persist longer. Depending on the protein, that can prolong activation or inhibition of a pathway.
8. A cell responds to the same signaling molecule in different ways depending on its cell type. Which explanation is most likely?
Explanation. Cellular response depends on the proteins present in that cell: receptors, relay proteins, transcription factors, and target genes. The same ligand can therefore cause different responses in different cell types. This is a central idea in cell communication and development.
9. Which example best represents paracrine signaling?
Explanation. Paracrine signaling acts locally on nearby cells. Synaptic signaling is a specialized short-distance form in which a neurotransmitter crosses a synaptic gap. Endocrine signaling uses long-distance hormones, and autocrine signaling occurs when a cell responds to its own signal.
10. Steroid hormones often affect gene expression because they can:
Explanation. Steroid hormones are nonpolar enough to cross the plasma membrane. They bind intracellular receptors, and the hormone-receptor complex can regulate transcription by interacting with DNA or transcription-related proteins. They do not function as ribosomes or mRNA templates.
11. A signaling pathway normally ends when the ligand is removed and relay proteins are reset. Why is this termination important?
Explanation. Signal termination keeps responses controlled and reversible. Ligand removal, GTP hydrolysis, second-messenger breakdown, and dephosphorylation can reset pathways. Without termination, cells may show inappropriate sustained responses, such as excess growth signaling.
12. In quorum sensing, bacteria alter gene expression when a secreted signaling molecule reaches a threshold concentration. What does this threshold usually indicate?
Explanation. Quorum sensing lets bacteria coordinate behavior based on population density. As more cells secrete the signal, its concentration rises; reaching a threshold indicates enough nearby cells for a coordinated response such as biofilm formation or bioluminescence.
📘 Want a full structured course and official-style practice tests? Browse top-rated AP Exams prep books and courses. Some links are affiliate links; we may earn a commission at no cost to you.
advertisement
FAQ
What are the main stages of cell communication on AP Biology?
Use the three-stage model: reception, transduction, and response. A signal is detected by a receptor, relay molecules pass the signal through the cell, and the cell changes activity such as enzyme function, ion flow, secretion, movement, or gene expression.
What receptor types should I know for AP Biology cell signaling?
Know the basic logic of G protein-coupled receptors, receptor tyrosine kinases, ligand-gated ion channels, and intracellular receptors. Focus on how ligand binding changes protein activity and how that leads to a response, rather than memorizing every named pathway.
How do I avoid mistakes on signaling pathway questions?
Track location and sequence. Ask whether the ligand is outside or inside the cell, whether the receptor is membrane-bound or intracellular, what gets activated next, and how the response is shut off. Many distractors confuse first messengers, second messengers, receptors, and final responses.