Plant Physiology

Step 1: Submerged plants का परिचय.
जलमग्न पौधों की पत्तियों में stomata (रंध्र) अनुपस्थित रहते हैं क्योंकि ये पौधे सीधे जल से गैसों का आदान-प्रदान कर लेते हैं।

Step 2: विकल्पों का विश्लेषण.
(A) दोनों सतह पर → terrestrial plants में।
(B) ऊपरी सतह पर → floating leaves में।
(D) निचली सतह पर → सामान्य terrestrial leaves में।

Step 3: निष्कर्ष.
सही उत्तर है (C) किसी भी सतह पर नहीं होते हैं।

Step 1: Understand CO2 fixation pathways.
Plants fix CO2 in two main ways: C-3 and C-4 pathways. In C-4 plants, CO2 is first fixed into a 4-carbon compound, using phosphoenol pyruvate (PEP) as a receptor.
Step 2: Review the options.
- C-3 plants fix CO2 directly into a 3-carbon compound via the Calvin cycle, and they do not have phosphoenol pyruvate as a CO2 receptor.
- C-4 plants, like maize and sugarcane, have phosphoenol pyruvate as a CO2 receptor during the initial steps of photosynthesis.
- C-6 plants are not a recognized category for CO2 fixation.
- Option (D) is incorrect because only C-4 plants use PEP for CO2 fixation.
Step 3: Conclude.
C-4 plants are the ones that use phosphoenol pyruvate as a CO2 receptor, making option (B) the correct answer.
Final Answer:

Step 1: Understand plant stress hormones.
Abscisic acid (ABA) is the primary stress hormone in plants that helps them respond to environmental stress such as drought and salinity.
Step 2: Review the options.
- Ethylene is a hormone involved in fruit ripening and stress responses but not directly a "stress" hormone.
- G.A.3 (Gibberellic acid) is involved in growth and development, not stress responses.
- I.A.A. (Indole-3-acetic acid) is a plant growth regulator, not a stress hormone.
- Abscisic acid (ABA) is the correct stress hormone, as it is involved in stress adaptation and regulation of processes like stomatal closure under drought conditions.
Step 3: Conclude.
Abscisic acid (ABA) is the stress hormone in plants, making option (D) the correct answer.
Final Answer:

Step 1: Understand the structure of chlorophyll.
Chlorophyll is the pigment responsible for the green color in plants and is crucial for photosynthesis. It contains a porphyrin ring with a central metal ion that plays a key role in its function.
Step 2: Review the options.
- Iron is the metal ion found at the center of the porphyrin ring in chlorophyll, which allows chlorophyll to capture light energy.
- Manganese is important in photosynthesis, but not at the center of the chlorophyll molecule.
- Copper is not present at the center of chlorophyll, though it is essential for other enzymatic functions.
- Magnesium is not at the center of chlorophyll's porphyrin ring but is instead a key element in other biological processes.
Step 3: Conclude.
Iron is present at the center of the porphyrin ring in chlorophyll, making option (A) the correct answer.
Final Answer: