Q31 - Plant Biology Assertion-Reason Questions
In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as:
- a if both Assertion and Reason are true, and the Reason is the correct explanation of Assertion.
- b if both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
- c if Assertion is true, but Reason is false.
- d if the Assertion is false.
Q31.1. Assertion: Water is oxidized to oxygen during the light-dependent reactions of photosynthesis. Reason: Water oxidation is carried out by the photosystem I complex.
Q31.2. Assertion: Cytokinins exhibit polar transport in plants. Reason: By using the polar transport system, cytokinin movement can be maintained regardless of changes in phloem transport.
Q31.3. Assertion: There is a meristematic phase of growth at both the root apex and shoot apex, because the cells are constantly dividing. Reason: There is a lot of protoplasm in the cells of this region, but no nucleus.
Q31.4. Assertion: A plant exposed to high salinity stress exhibits reduced transpiration rate compared to a plant growing under normal conditions. Reason: Water conduction in plant tissues is regulated by an equilibrium between water absorbed by the roots and water transpired from the leaves.
Q31.5. Assertion: Plants produce many phenolic compounds that play an important role in their defense responses. Any manipulation in the production of phenolic compounds through genetic engineering would always lead to drastic retardation in plant growth and development. Reason: Phenolic compounds are primary metabolites that regulate cell growth and development at many stages.
Q31.6. Assertion: It is not possible for plants to utilize atmospheric nitrogen for their metabolism. As a result, they require nitrogen-fixing microorganisms (e.g. rhizobia) in the soil to provide nitrogen in usable form. Reason: The nitrogen fixed by Rhizobium is used in their own metabolism and becomes available to plants and fungi only when they die and decay.
Q31.7. Assertion: Plant cells may die if they are exposed to severe abiotic stress like heat, salinity, drought etc. for a long period. Reason: In response to abiotic stresses, among other pathologies, plants produce reactive oxygen species (ROS), which are highly reactive and toxic.
Q31.8. Assertion: Sepals, petals, stamens and pistils are parts of a flower. Reason: The petiole and lamina are parts of the stem.
Q31.9. Assertion: Green leaves make their energy-rich compounds by the process of photosynthesis. Reason: Plants use CO2 and water in the presence of sunlight to make energy-rich compounds.
Q31.10. Assertion: Hydroponically grown plants (grown in the absence of soil) are grown in a nutrient solution in which air is bubbled. Reason: The bubbling solution increases the relative humidity within the plant chamber which is needed for plant growth.
Q31.11. Assertion: All cells of a plant have almost identical DNA, but there are different cell types and tissues within a plant. Reason: Factors such as internal environment, hormones, light/dark etc. determine which subset of the genome is expressed.
Q31.12. Assertion: In general, dicotyledonous mesophyte leaves have fewer stomata and thicker cuticle on their upper surface, compared to their lower surface. Reason: The upper surface of the leaves is exposed to greater light intensity.
Question reproduced from IBO 2023, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF