Name one organ built as a tube from a folded sheet.

• A finger bone
• The neural tube, later brain and spinal cord
• A hair strand

A flat sheet of cells rolls up and seals its edges. What did it become?

• A single cell
• A pile of ash
• A tube

Programmed cell death carves fingers by removing the webbing between digits.

Circle one:   True   False

You want to watch a heart tube form live in one embryo. Which organism strength do you need?

• The fastest possible breeding cycle
• The largest possible adult body
• A transparent embryo you can see through

Lungs need a large surface in a small chest. Which move builds them?

• Repeated branching of a tube
• Melting the tube back into a sheet
• Freezing all cell division

You want to break hundreds of genes and find which ones stop tube sealing. Which strength matters most?

• Transparency of the embryo
• Fast breeding and easy mutation
• A long adult lifespan

A mutant keeps webbed digits at birth. Which move failed, and what would confirm it?

• Branching failed; check the lungs
• Folding failed; check the neural tube
• Pruning by death failed; look for surviving web cells

A lab studies lung branching only in fish and declares the mechanism universal. A reviewer objects. What is the strongest objection?

• Fish have no lungs like ours, so mammal confirmation is missing
• Fish are transparent, which ruins the result
• Branching never happens in fish