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.

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.

1) Which term most accurately describes the nutritional mode of healthy P. bursaria?

2) Which term accurately describes the behavior of Paramecium species that lack zoochlorellae in an aquarium with light coming from one side only?

3) Which term best describes the symbiotic relationship of well-fed P. bursaria to their zoochlorellae?

4) The motility that permits P. bursaria to move toward a light source is provided by

5) A P. bursaria cell that has lost its zoochlorellae is said to be aposymbiotic. It might be able to replenish its contingent of zoochlorellae by ingesting them without subsequently digesting them. Which of the following situations would be most favorable to the reestablishment of resident zoochlorellae, assuming compatible Chlorella are present in P. bursaria's habitat?

6) A P. bursaria cell that has lost its zoochlorellae is aposymbiotic. If aposymbiotic cells have population growth rates the same as those of healthy, zoochlorella-containing P. bursaria in well-lit environments with plenty of prey items, then such an observation would be consistent with which type of relationship?

7) Theoretically, P.bursaria can obtain zoochlorella either vertically (via the asexual reproduction of its mother cell) or horizontally (by ingesting free-living Chlorella from its habitat). Consider a P. bursaria cell containing zoochlorellae, but whose habitat lacks free-living Chlorella. If this cell subsequently undergoes many generations of asexual reproduction, if all of its daughter cells contain roughly the same number of zoochlorellae as it had originally contained, and if the zoochlorellae are all haploid and identical in appearance, then what is true?

A) The zoochlorellae also reproduced asexually, at an increasing rate over time.

B) The zoochlorellae also reproduced asexually, at a decreasing rate over time.

C) The zoochlorellae also reproduced asexually, at a fairly constant rate over time.

D) The zoochlorellae reproduced sexually, undergoing heteromorphic alternation of generations.

E) The zoochlorellae reproduced sexually, undergoing isomorphic alternation of generations.

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