Quick revision: every question with its correct answer. For the full explanation, open the relevant test and tap View Solution.
3.3 Blastula & ICM — Test 1
Q1. The solid ball of cells formed by early cleavage, before a cavity appears, is the:✓ Morula
Q2. The fluid-filled cavity of the blastula is called the:✓ Blastocoel
Q3. In mammals, compaction of the early embryo involves:✓ Blastomeres flattening against each other and forming tight junctions
Q4. Compaction depends on the activity of actin filaments. An inhibitor of which enzyme would block blastula (blastocyst) formation?✓ GSK3-beta
Q5. In the mammalian blastocyst, the inner cell mass (ICM) gives rise to:✓ The embryo proper (and some extra-embryonic tissue)
Q6. The outer cell layer of the mammalian blastocyst, which forms the placenta, is the:✓ Trophoblast (trophectoderm)
Q7. The 'thin layer of cells' of the blastocyst that invades the uterus to begin forming the placenta is the:✓ Trophoblast
Q8. Pluripotency of the inner cell mass is maintained by a core of three transcription factors:✓ Oct4, Sox2 and Nanog
Q9. In the trophoblast-versus-ICM decision, the transcription factor that drives the trophoblast fate is:✓ Cdx2
Q10. The Hippo signalling pathway helps decide ICM versus trophoblast. In inner cells, the pathway is active so that:✓ Phosphorylated YAP stays out of the nucleus, lowering Cdx2 and favouring ICM
Q11. In outer cells of the early mammalian embryo, YAP enters the nucleus and binds TEAD4 to:✓ Activate Cdx2 and promote the trophoblast fate
Q12. The earliest indication of the first differentiation event in the mammalian embryo is:✓ Compaction
Q13. The hollow blastula typical of many animals (e.g. sea urchin) is called a:✓ Coeloblastula
Q14. A solid blastula with no blastocoel is called a:✓ Stereoblastula
Q15. Cavitation in the mammalian embryo refers to the formation of the:✓ Fluid-filled blastocoel cavity of the blastocyst
Q16. In birds, the blastoderm splits to form an upper epiblast and lower hypoblast, with a cavity between them. This cavity is the:✓ Blastocoel-like subgerminal space
Q17. hCG (human chorionic gonadotropin), important for implantation, is produced by the:✓ Trophoblast (extra-embryonic tissue)
Q18. Experiments show that biologically active hCG is needed for implantation because:✓ Immune-neutralizing hCG in a normal uterus blocks implantation
Q19. Prior to blastocyst formation, each blastomere expresses BOTH Cdx2 and Oct4 and can become either ICM or trophoblast. This shows the blastomeres are initially:✓ Bipotent (uncommitted between the two fates)