AP Biology: Cell Communication and Cell Cycle — Practice Questions & Answers
How cells send, receive, and respond to signals through signal transduction pathways, and how the cell cycle is regulated by checkpoints, cyclins, and CDKs — with cancer as a breakdown of that control.
500 practice questions available for this unit — here are 10 with full answers and explanations.
A muscle cell releases a chemical signal that diffuses only a short distance to act on a neighboring cell. Which type of cell signaling is described?
Long-distance endocrine signaling
Local signaling
Signal transduction within a single cell
Negative feedback
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WhyLocal signaling involves signaling molecules (such as paracrine signals) that travel only a short distance to nearby target cells. Long-distance signaling, by contrast, uses hormones carried through the bloodstream.
2Multiple choice · Easy
In a typical signal transduction pathway, what is the correct order of the three stages?
Transduction -> reception -> response
Reception -> transduction -> response
Response -> reception -> transduction
Reception -> response -> transduction
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WhyCell signaling proceeds in three stages: reception (the signal binds a receptor), transduction (the signal is relayed and often amplified through the cell), and response (a cellular change occurs).
3Multiple choice · Easy
Which molecule commonly acts as a second messenger in signal transduction pathways?
DNA
Cyclic AMP (cAMP)
The original extracellular ligand
Cellulose
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WhyCyclic AMP (cAMP) is a classic second messenger. After a signal binds a G protein-coupled receptor, adenylyl cyclase converts ATP into cAMP, which relays the signal inside the cell. DNA, ATP itself, and the original ligand are not second messengers.
4Multiple choice · Easy
During which broad phase of the cell cycle does a cell spend most of its time, growing and replicating its DNA?
Mitosis
Cytokinesis
Interphase
Prophase
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WhyInterphase (consisting of G1, S, and G2) is the longest part of the cell cycle. The cell grows, carries out normal functions, and replicates its DNA during S phase. Mitosis (M phase) is comparatively brief.
5Multiple choice · Medium
A hydrophilic signaling molecule cannot cross the plasma membrane. Where must its receptor be located for the cell to respond?
In the nucleus
On the plasma membrane (cell surface)
Free in the cytoplasm only
Inside the mitochondria
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WhyBecause hydrophilic (water-soluble) signals cannot pass through the hydrophobic interior of the membrane, they must bind to receptors embedded in the plasma membrane (cell-surface receptors). Hydrophobic/nonpolar signals can cross the membrane and bind intracellular receptors.
6Multiple choice · Medium
Why does a small number of signaling molecules often produce a large cellular response?
Each signaling molecule permanently binds thousands of receptors
The signal is amplified at each step of the transduction cascade
Signaling molecules replicate themselves inside the cell
The receptor copies the ligand many times
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WhySignal transduction pathways frequently involve a phosphorylation cascade in which each activated enzyme (kinase) activates many copies of the next, amplifying the signal at each step. This allows a few signal molecules to trigger a large response.
7Multiple choice · Medium
During the regulation of blood glucose, rising insulin lowers blood sugar, which in turn reduces further insulin release. This is an example of what kind of feedback?
Positive feedback
Negative feedback
Signal amplification
Long-distance signaling failure
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WhyNegative feedback occurs when the response to a stimulus reduces or reverses the original stimulus, helping maintain homeostasis. Here, the lowering of blood glucose damps down further insulin secretion.
8Multiple choice · Medium
Which event is characteristic of metaphase of mitosis?
Sister chromatids separate and move to opposite poles
Chromosomes line up along the metaphase plate
The nuclear envelope re-forms
DNA is replicated
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WhyDuring metaphase, the duplicated chromosomes (each made of two sister chromatids) align single-file along the metaphase plate at the cell's equator. Separation of sister chromatids occurs in anaphase.
9Multiple choice · Medium
Cyclin-dependent kinases (CDKs) are only active when bound to which class of regulatory proteins?
Growth factors
Cyclins
Second messengers
Tumor suppressor mRNAs
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WhyCDKs require binding to cyclins to become active. Cyclin levels rise and fall through the cycle, so cyclin-CDK complexes form at specific times to drive the cell past checkpoints. Without cyclin, the CDK is inactive.
10Multiple choice · Hard
A drug blocks the GTPase activity of a Ras protein, leaving Ras permanently in its GTP-bound state. What is the most likely consequence for the cell?
Ras can no longer transmit any signal
Ras continuously signals for cell growth even without a stimulus
The cell halts permanently in G0
DNA replication is prevented entirely
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WhyRas is a G protein that is active when bound to GTP and inactive after it hydrolyzes GTP to GDP. If GTPase activity is lost, Ras stays continuously active, sending uninterrupted growth signals downstream. This can drive uncontrolled proliferation, a hallmark of cancer.
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Cell communication: The exchange of information between cells, allowing them to coordinate activities, respond to their environment, and maintain proper function within an organism.
Cell signaling: The overall process by which a cell detects an external or internal signal and converts it into a specific cellular response.
Signal transduction: The series of molecular events that carries a signal from a receptor through the interior of a cell, ultimately producing a response.
Signal transduction pathway: An ordered sequence of molecular interactions that relays a signal from the cell membrane into the cell, often amplifying it along the way to generate a response.
Reception: The first stage of cell signaling, in which a signaling molecule binds to a specific receptor on or inside the target cell.
Transduction: The middle stage of cell signaling, in which the bound receptor converts the signal into a form that can trigger changes inside the cell, frequently through a chain of relay molecules.
Response: The final stage of cell signaling, in which the transduced signal causes a specific cellular activity such as gene expression, enzyme activation, or a change in metabolism.
Ligand: A signaling molecule that binds to a specific receptor, fitting it like a key in a lock and triggering a change in the receptor's shape or activity.