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5.1 Dictyostelium — Test 1
Q1. Dictyostelium discoideum amoebae feed on bacteria when food is plentiful, but on starvation they aggregate into a fruiting body. This makes it a model for the evolution of:✓ Multicellularity
Q2. The morphogen that controls aggregation and differentiation in Dictyostelium is:✓ cAMP (cyclic AMP)
Q3. At the time of aggregation, each Dictyostelium amoeba has the ability to:✓ Make, receive and relay cAMP
Q4. aca-deficient (adenylyl cyclase A) Dictyostelium cells can be made to aggregate by:✓ Exposing them to artificial pulses of cAMP
Q5. RegA in Dictyostelium is a:✓ Phosphodiesterase that degrades cAMP intracellularly
Q6. The Dictyostelium fruiting body consists of which two differentiated cell types?✓ Stalk cells and spore cells
Q7. The migrating multicellular stage of Dictyostelium (before the fruiting body) is called the:✓ Slug (pseudoplasmodium)
Q8. In Dictyostelium, cells respond to cAMP and move toward its source. This directed movement is called:✓ Chemotaxis
Q9. The relay of cAMP from cell to cell in Dictyostelium produces:✓ Outward-spreading waves of cAMP
Q10. Prestalk and prespore cells in the Dictyostelium slug are an early example of:✓ Cell differentiation within a simple multicellular organism
Q11. Why is the formation of stalk cells in Dictyostelium considered 'altruistic'?✓ Stalk cells die so that the spore cells can survive and disperse
Q12. Dictyostelium is especially useful as a model because it allows the study of:✓ Chemotaxis, cell signalling and differentiation in a simple system
Q13. During Dictyostelium aggregation, the cAMP signal moves outward as spiral or concentric waves because cells:✓ Relay the signal and then become briefly refractory before responding again
Q14. In Dictyostelium, the cell-surface protein that detects cAMP is the:✓ cAMP receptor (cAR1, a G-protein-coupled receptor)
Q15. Prestalk cells in the Dictyostelium slug tend to sort to the:✓ Anterior (front) of the migrating slug
Q16. The differentiation of prestalk versus prespore cells in Dictyostelium is influenced by the signalling molecule DIF, which is a:✓ Chlorinated small molecule that promotes stalk-cell fate
5.1 Dictyostelium — Test 2
Q17. The tip of the Dictyostelium slug behaves like an embryonic organizer because it:✓ Controls the movement and patterning of the rest of the slug
Q18. During culmination, the Dictyostelium fruiting body is built so that the stalk:✓ Lifts the spore mass up off the substrate for better dispersal
Q19. Dictyostelium is often called a model of facultative multicellularity because it:✓ Lives as single cells when fed but becomes multicellular only on starvation
Q20. A practical advantage that makes Dictyostelium a strong genetic model is that it:✓ Has a haploid genome, so mutations show their effect directly
Q21. If Dictyostelium cells were unable to make the cAMP receptor (cAR1), they would:✓ Fail to sense cAMP and not aggregate
Q22. The streaming of Dictyostelium amoebae into aggregation centres produces branching, river-like patterns because cells:✓ Move head-to-tail following one another up the cAMP gradient
Q23. In the Dictyostelium life cycle, spores are advantageous because they:✓ Are dormant and resistant, surviving until food returns
Q24. The decision of a Dictyostelium cell to become stalk or spore is partly determined by:✓ Its nutritional/cell-cycle state at the time of starvation
Q25. Chemotaxis in Dictyostelium works by cells detecting:✓ Differences in cAMP concentration across their surface
Q26. The use of cAMP both as an intracellular second messenger and an extracellular signal in Dictyostelium illustrates:✓ How a single molecule can be re-used for cell-cell communication
Q27. Compared with a true animal embryo, the Dictyostelium 'multicellular' body differs in that its cells:✓ Come together by aggregation rather than staying together after division
Q28. Adhesion molecules expressed during Dictyostelium aggregation are important because they:✓ Hold the streaming and aggregated cells together
Q29. Removing RegA function (the cAMP phosphodiesterase) in Dictyostelium would tend to:✓ Raise intracellular cAMP and disturb the normal developmental timing
Q30. The Dictyostelium slug migrates toward light and heat, behaviour known as:✓ Phototaxis and thermotaxis
Q31. Why is the death of stalk cells in Dictyostelium of interest to biologists studying cooperation?✓ Stalk cells forgo reproduction to help spore cells survive, an example of altruism
Q32. Overall, Dictyostelium discoideum is valuable because it lets researchers study, in one simple organism:✓ Chemotaxis, signal relay, cell sorting, differentiation and cooperation