Acetabularia are enormously large (2—4 cm long), single-celled green algae that resemble mushrooms. They consist of a cap, a stalk, and a root-like structure called a "rhizoid," which contains the large cell nucleus. In 1943, Joachim Hämmerling exchanged the nuclei of an Acetabularia mediterranea (which forms a flat cap) with that of an Acetabularia crenulata (which forms a castellated cap).

What result would you expect from this experiment? Which basic concept does it confirm?

In Joachim Hämmerling's 1943 experiment with the Acetabularia algae, he swapped the nuclei between two species, Acetabularia mediterranea and Acetabularia crenulata.

Acetabularia mediterranea is known for forming a flat cap, while Acetabularia crenulata forms a castellated cap. By exchanging the nuclei of these two species, Hämmerling aimed to observe how the nucleus influences the development of the cap structure in these algae.

Expected Result

After the transplantation of the Acetabularia mediterranea's nucleus into the cell of Acetabularia crenulata, it is expected that the alga will develop a cap structure typical of Acetabularia mediterranea (a flat cap). Conversely, a cell with the nucleus of Acetabularia crenulata will develop a castellated cap, typical of the crenulata species.

Basic Concept Confirmed

This experiment supports and confirms the concept of the genetic basis of cell differentiation and development. Specifically, it underscores the role of the nucleus as the control center for cellular activities, primarily because it contains the genetic material (DNA) that dictates the structure and function of the organism.

Hämmerling's experiment illustrates that the nucleus regulates the type of cap produced by the alga, thereby confirming that genetic information present in the nucleus guides cellular morphology and development even in a notoriously large and complex single-celled organism like Acetabularia.