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United StatesBiology

Unit 4: Cell Communication and Cell Cycle

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do cells communicate with one another over short and long distances?

Topic 4.1 Cell Communication: describe the ways cells communicate, including direct contact and chemical signalling over short and long distances.
A focused answer to AP Biology Topic 4.1, covering direct contact signalling, paracrine, autocrine, synaptic and endocrine signalling, and how signal type relates to distance and target.
9 min answer →

What are the phases of the cell cycle, and what happens in each?

Topic 4.5 Cell Cycle: describe the phases of the cell cycle, including interphase and mitosis, and explain how the events of each phase produce two genetically identical cells.
A focused answer to AP Biology Topic 4.5, covering G1, S, G2, the phases of mitosis, cytokinesis and G0, and how the cycle produces two genetically identical daughter cells, with a worked timing calculation.
10 min answer →

How do negative and positive feedback keep biological systems regulated?

Topic 4.4 Feedback: explain how negative feedback maintains homeostasis and how positive feedback amplifies a response, using examples from cellular and organismal systems.
A focused answer to AP Biology Topic 4.4, covering negative feedback and homeostasis, positive feedback and amplification, set points, and how feedback data are analyzed, with a worked chi-square example.
10 min answer →

How does a signal arriving at a cell get converted into a response inside the cell?

Topic 4.2 Introduction to Signal Transduction: describe the reception, transduction and response stages of a signalling pathway, and the roles of receptors, ligands and second messengers.
A focused answer to AP Biology Topic 4.2, covering the three stages of signal transduction (reception, transduction, response), membrane and intracellular receptors, ligands, relay molecules and second messengers.
9 min answer →

How is the cell cycle controlled, and what happens when that control fails?

Topic 4.6 Regulation of the Cell Cycle: explain how checkpoints and regulatory molecules control progression through the cell cycle, and how loss of control leads to cancer.
A focused answer to AP Biology Topic 4.6, covering cell-cycle checkpoints, cyclins and cyclin-dependent kinases, growth factors, the link to signal transduction, and how loss of regulation causes cancer.
10 min answer →

How do signal transduction pathways amplify a signal, and what happens when they are altered?

Topic 4.3 Signal Transduction Pathways: explain how signalling pathways relay and amplify a signal to produce a response, and how mutations or chemicals that change the pathway affect the cell.
A focused answer to AP Biology Topic 4.3, covering relay molecules, phosphorylation cascades, signal amplification, the variety of cellular responses, and how mutations and chemicals alter pathways.
10 min answer →