Question

What modifications are Plants adapted to low light intensity?
A. Leaves are modified to spines.
B. Presence of large photosynthetic units with size more than that of sun plants.
C. Fix $CO_2$ at a rate higher than the sun plants.
D. A more extended root system.

Answer 1

Hint: Photosynthesis is a process in which green plants utilize light energy and transform it into chemical energy allowing plants to make their food. Shade tolerance has lower photosynthetic rates.

Complete answer:
Shade-tolerant plants have lower photosynthetic rates, grow broader, thinner leaves to catch more sunlight relative to the cost of producing the leaf. Shade-intolerant plants are also usually adapted to make less use of soil nutrients than shade-tolerant plants.
Plants have specific requirements for the light. Plants growing in shade have dark green leaves. Plants growing in the sun have less green leaves. Chlorophyll content will be more in the shade-loving plants. This is an adaptation to help shade growing plants capture the optimum amount of light for the process of photosynthesis. In other words, plants adapted to low light intensity, have larger photosynthetic unit size than the plants growing in bright sunlight.
The Proteinaceous Photosynthetic unit will increase when the light levels decline. At lower light levels, chloroplasts have a larger PSU to increase the probability that a photon will strike the chlorophyll antenna. Thus, plants adapted to low light intensity have larger photosynthetic unit size than the sun plants. Plants adapted to low light intensity do not have a higher rate of $CO_2$ fixation, more extended root system and leaves are not modified to spines.

Hence, the correct answer is option (B).

Additional information:
The leaf parts become modified into spines to protect the plants from grazing animals and excessive transpiration.
In some plants, the roots change their shape. They get modified to absorb and transport water and minerals. They are modified for support, food storage, and respiration.

Note: Plants adapted to low light intensity have a higher rate of $CO_2$ fixation than the sun plants. Plants adapted to shade can utilize far-red light (about 730 nm) more effectively than plants adapted to full sunlight, so they have a larger photosynthetic unit size than the sun plants.