Final answer:
The structure common to all protozoa is Cytoplasm. This jelly-like substance is a component of all eukaryotic cells, including the diverse group of organisms known as protozoa, providing a matrix for cellular processes. The correct answer is option c.
Step-by-step explanation:
Protozoa are a diverse group of single-celled, eukaryotic organisms belonging to the kingdom Protista. While protozoa exhibit significant diversity in their structures and behaviors, they share certain common features, with the presence of a nucleus being a fundamental characteristic.
Nucleus: All protozoa possess a nucleus, which is a membrane-bound organelle containing the organism's genetic material in the form of DNA. The nucleus regulates cellular activities and plays a crucial role in controlling gene expression, cellular division, and the overall functioning of the cell.
Other structures like cilia (hair-like projections) and cytoplasm (the cell's fluid substance) are found in many protozoa, but they are not universal to all members of this diverse group. While some protozoa have cilia for movement, others may use flagella, pseudopodia, or have no specialized structures for locomotion.
Additionally, protozoa can exhibit various shapes, such as irregular or asymmetrical forms, and they do not necessarily have a regular shape common to all species within this group.
However, the presence of a membrane-bound nucleus containing genetic material is a defining feature universally shared by all protozoa, distinguishing them as eukaryotic organisms.