Question

certains species of sea slugs feed on algae. when these animals eat algae, they penetrate the cell wall of the the algal cells, digest the cellular content, and incorporate the algal chloroplasts into the intestinal cells of their digestive tracts. this process is called kleptoplasty.

researchers examined the role of kleptoplasty in the sea slug elysia viridis. the researchers compared the growth of adult e. viridis maintained under three conditions for 25 days:

• control: sea slugs kept in lighted aquariums with access to algae
• light - starved: sea slugs kept in lighted aquariums with no access to algae
• dark - starved: sea slugs kept in dark aquariums with no access to algae

the table below shows the results of this experiment.

	condition	day
weight (mg)	control	18	27
	light - starved	18	12
	dark - starved	18	4
length (mm)	control	13	15
	light - starved	14	15
	dark - starved	13	7

data courtesy of cartaxana et al 2017. scientific reports. licensed under cc by 4.0

which conclusion regarding photosynthesis in e. viridis is supported by the data?
a. the body of e. viridis is partially translucent to allow light energy to reach intestinal cells.
b. the chloroplasts incorporated into e. viridis intestinal cells need algae to produce chemical energy.
c. e. viridis consume more co₂ to produce sugars when in the dark than when in the light.
d. e. viridis consume more o₂ for photosynthetic reactions when in the light than when in the dark.

Explanation:

• Option A: The experiment data focuses on growth (weight, length) under different conditions, not on the body's translucency. No data supports this.
• Option B: In the control group (access to algae), weight and length increase. In light - starved (no algae, light present) and dark - starved (no algae, dark) groups, growth is stunted (weight decreases, length in dark - starved decreases). This suggests that the chloroplasts (from algae) in intestinal cells need algae (or their products) to produce chemical energy for growth.
• Option C: Photosynthesis requires light, so E. viridis should consume more \(CO_2\) (for photosynthesis) in light, not dark. This is incorrect.
• Option D: Photosynthesis produces \(O_2\), it does not consume \(O_2\) for photosynthetic reactions. Respiration consumes \(O_2\), so this is incorrect.

Answer:

B. The chloroplasts incorporated into E. viridis intestinal cells need algae to produce chemical energy.