Addition of blue light to saturating red light causes stomata to:
Correct option is C, Open further. In PSS-Sec-E-Sensory biology problems like this, the accurate statement is Open further; the others are common mix-ups. Not these: A) Remain unchanged; B) Close; D) Undergo damage. Tissue transport questions usually turn on xylem vs phloem, living vs dead cells, or source vs sink.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.