Q.62 Statements given below are either TRUE (T) or FALSE (F). Find the correct combination.
P. Regulation of cell cycle progression depends on cyclin dependent kinase (CDK) and protease
activity.
Q. In photosynthesis, oxidation of water produces O2 and releases electrons required by
photosystem I (PSI).
R. Photorespiratory reaction occurring in oxidative photosynthetic carbon (C2) pathway involves a
cooperative interaction among three organelles: chloroplast, peroxisome and mitochondria.
S. Ethylene acts as a promoter of senescence and cytokinins act as a senescence antagonist.
(A) P-T, Q-F, R-T, S-F (B) P-T, Q-T, R-T, S-F
(C) P-T, Q-F, R-F, S-T (D) P-T, Q-F, R-T, S-T
Cell cycle regulation and photosynthesis processes are key topics in biology exams, with the correct combination for this question being (D) P-T, Q-F, R-T, S-T.
Correct Answer
The right option is (D) P-T, Q-F, R-T, S-T. P is true as CDKs pair with cyclins for progression, aided by ubiquitin-proteasome degradation (protease activity) of cyclins. Q is false since water oxidation occurs at PSII, not PSI; PSI receives electrons from PSII. R and S are true: photorespiration spans chloroplast-peroxisome-mitochondria, and ethylene promotes while cytokinins delay senescence.
Statement P: True
Regulation of cell cycle progression depends on cyclin-dependent kinase (CDK) and protease activity. CDKs activate via cyclin binding and are regulated by synthesis/degradation cycles, where APC/C ubiquitin ligase (protease pathway) degrades cyclins to reset phases like G1/S or metaphase-anaphase. This ensures timely progression without unchecked division.
Statement Q: False
In photosynthesis, oxidation of water produces O2 and releases electrons required by photosystem I (PSI). Water splitting (photolysis) happens at PSII’s oxygen-evolving complex, supplying electrons to PSII then PSI via the chain; PSI uses these for NADPH, not direct water electrons.
Statement R: True
Photorespiratory reaction occurring in oxidative photosynthetic carbon (C2) pathway involves a cooperative interaction among three organelles: chloroplast, peroxisome and mitochondria. Glycolate from Rubisco’s oxygenase goes chloroplast → peroxisome (glyoxylate to glycine) → mitochondria (glycine to serine, NH3 release), recovering carbon at C2 cycle cost.
Statement S: True
Ethylene acts as a promoter of senescence and cytokinins act as a senescence antagonist. Ethylene triggers leaf/fruit aging via gene expression for degradation; cytokinins maintain chlorophyll, delay protein loss, opposing senescence in leaves and delaying aging.
Quick T/F Summary
| Statement | T/F | Key Reason |
|---|---|---|
| P (CDK & protease) | T | Cyclin degradation via proteasome |
| Q (Water → PSI) | F | Water oxidizes at PSII |
| R (Photorespiration organelles) | T | Chloroplast-peroxisome-mitochondria cycle |
| S (Ethylene vs cytokinins) | T | Promote vs delay senescence |
