Leslie argues that an organism called a Euglena is a plant because it is eukaryotic, has a nucleus, makes its own food, and is unicellular. Where is Leslie's error?

Euglena lacks cell wall

Explanation:

Although euglena has many features of plant cells like

But it lacks cell wall which is a defining feature of plant cells. Instead of cell wall it has a pellicle which is made of protein and has a protective function for euglena. Thus it can not be clearly classified as a plant.

come closer and become far apart and become steam/gas