The next few questions refer to the following description.
Healthy individuals of Paramecium bursaria contain photosynthetic algal endosymbionts of the genus Chlorella. When within their hosts, the algae are referred to as zoochlorellae. In aquaria with light coming from only one side, P. bursaria gathers at the well-lit side, whereas other species of Paramecium gather at the opposite side. The zoochlorellae provide their hosts with glucose and oxygen, and P. bursaria provides its zoochlorellae with protection and motility.? P. bursaria can lose its zoochlorellae in two ways: (1) if kept in darkness, the algae will die; and (2) if prey items (mostly bacteria) are absent from its habitat, P. bursaria will digest its zoochlorellae.
-Which term accurately describes the behaviour of Paramecium species that lack zoochlorellae in an aquarium with light coming from one side only?
A)positive chemotaxis
B)negative chemotaxis
C)positive phototaxis
D)negative phototaxis

Question

Quizplus · Accepted Answer

Other species of Paramecium gather at the opposite side because they exhibit negative phototaxis, while P. bursaria exhibits positive phototaxis towards the well-lit side due to the presence of its zoochlorellae. Therefore, Paramecium species that lack zoochlorellae would also exhibit negative phototaxis.

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