A
Higher rate of $CO_2$ fixation than the sun plants
B
More extended root system
C
Leaves modified to spines
D
Larger photosynthetic unit size than the sun plants
The answer is D.
Solution
Shade plants (sciophytes) live under low light intensity, for example on the forest floor. To trap as much of the scarce light as possible, they have more chlorophyll per reaction centre, i.e. a larger photosynthetic unit size (more antenna pigment molecules feeding each reaction centre), and larger grana with more thylakoids. Their rate of $CO_2$ fixation is lower than that of sun plants, because light is limiting. Extended root systems and spiny leaves are adaptations of plants of dry (xeric) habitats, not of shade. So plants adapted to low light intensity have a larger photosynthetic unit size than sun plants.
ConceptShade plants and photosynthetic unit size
Photosynthesis in Higher Plants in past papers
91 questions from this chapter have appeared across 26 exam years.
