Chloroplast Alignment & Light Intensity — NEET Biology
📚 Practice ConceptYou would recollect from previous unit that the mesophyll cells in the leaves, have a large number of chloroplasts. Usually the chloroplasts align themselves along the walls of the mesophyll cells, such that they get the optimum quantity of the incident light. When do you think the chloroplasts will be aligned with their flat surfaces parallel to the walls? When would they be perpendicular to the incident light?
Which of the following statements regarding mesophyll cells and photosynthesis are NOT correct? S1: Mesophyll cells in C3 plants contain a large number of chloroplasts, optimally positioned to maximize light absorption. S2: The initial carboxylation of CO2 in C4 plants occurs in mesophyll cells, where RuBisCO enzyme is highly concentrated. S3: Light reactions, including the splitting of water, take place predominantly in the stroma of chloroplasts in mesophyll cells. S4: The biosynthetic phase of photosynthesis, which does not directly depend on light, is carried out in the mesophyll cytoplasm. S5: In C4 plants, the mesophyll cells transport 4-carbon acids to the bundle sheath cells for the release of CO2.
View solution & NCERT explanation
Correct answer: B — S2, S3 and S4
The question assesses the understanding of the roles and characteristics of mesophyll cells in photosynthesis, particularly contrasting C3 and C4 pathways, and the specific locations of photosynthetic processes. S1: Mesophyll cells in C3 plants have a large number of chloroplasts that align themselves along the walls to get the optimum quantity of incident light. This statement is correct. S2: In C4 plants, the primary CO2 acceptor (PEP) and the enzyme responsible for initial fixation (PEP carboxylase or PEPcase) are in the mesophyll cells. The RuBisCO enzyme, however, is concentrated in the bundle sheath cells. Therefore, this statement is NOT correct because RuBisCO is not highly concentrated in mesophyll cells of C4 plants. S3: Light reactions, including water splitting, occur on the thylakoid membranes within the chloroplasts, not predominantly in the stroma. The stroma is the site of dark reactions. Therefore, this statement is NOT correct. S4: The biosynthetic phase (dark reactions or Calvin cycle) occurs in the stroma of the chloroplasts, not in the mesophyll cytoplasm. Therefore, this statement is NOT correct. S5: In C4 plants, the 4-carbon compounds (like malic acid or aspartic acid) formed in mesophyll cells are transported to bundle sheath cells, where they are broken down to release CO2. This statement is correct. Based on the analysis, statements S2, S3, and S4 are NOT correct.
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Through deep analysis of NEET and NTA, 176 of the 180 ReNEET 2026 (June 21) questions were already in the MedicNEET question bank before the exam.
176/180MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.