If every cell has the same DNA, what actually makes them different in IB Biology terms?

In IB Biology, the key difference is gene expression, not gene possession. Cells build different transcriptomes by transcribing different subsets of genes. Those transcripts lead to different proteins, and proteins drive cell structure and function. A neuron expresses genes for synaptic signalling, while a muscle cell expresses genes for contractile proteins. The genome is like a full library, but each cell checks out different books. Your exam answers should state “same genome, different expression due to regulation.”

Are epigenetic changes permanent, and should I say that in IB Biology?

Some epigenetic marks are stable enough to persist through many cell divisions, which helps maintain specialization. That stability is why differentiated tissues keep their identity over time. However, epigenetic marks can also be reversible and responsive to signals, especially in regulatory regions. This flexibility lets cells adapt to environmental changes without mutating DNA. In IB Biology, it is safest to say epigenetic tags can be long-lasting but are not always permanent. Add chromatin accessibility and methylation as your mechanism.

Can a specialized cell change which genes it expresses?

Yes, gene expression can shift in response to hormones, stress, or signalling pathways. Cells constantly adjust transcription rates and mRNA stability to match conditions. That said, highly specialized cells tend to maintain a core expression pattern enforced by transcription factor networks and epigenetic marks. Dramatic identity changes are uncommon without reprogramming, but smaller expression changes are routine. In IB Biology, distinguish between “core identity genes” (stable) and “response genes” (dynamic). If you mention microRNAs, you also show awareness of post-transcription control.