Final answer:
The statement that unicellular eukaryotes cannot respond to environmental stimuli is false. These single-celled organisms have mechanisms to sense and react to changes in their environment, through various forms of taxis and signal transduction processes.
Step-by-step explanation:
The statement 'Unicellular eukaryotes cannot respond to environmental stimuli.' is false. Unicellular organisms, like multicellular ones, are capable of responding to environmental stimuli. This is a crucial ability for survival, allowing them to detect and react to changes in their environment, such as the presence of nutrients or toxins, changes in temperature, light, and other signals. Unicellular eukaryotes have complex mechanisms for signal transduction; they use parts of their cell structure like the plasma membrane to receive and process signals. Even though they do not have the same level of specialization and coordination as seen in multicellular organisms, they certainly are capable of sensing and responding to their surroundings.
For instance, single-celled organisms like protozoa can move toward or away from chemical signals in a process known as chemotaxis. This is a form of environmental response. Similarly, they may have receptors that can perceive light (phototaxis) or other signals and trigger a cellular response. Hence, the capacity to respond to environmental stimuli is not exclusive to multicellular organisms; unicellular eukaryotes exhibit this capability as well.