Photosynthesis In Higher Plants

The movement of electrons from plastocyanin to PSI does not result in proton translocation. Other processes like photolysis, quinone cycle, and NADP reduction contribute to proton gradient.

Chlorophyll 'b' appears yellow-green in the chromatogram due to its absorption properties.

Photorespiration leads to loss of energy as ATP is consumed and CO is released without producing sugars or NADPH. Hence, both the assertion and reason are true, and R explains A correctly.

Bulliform cells are large, thin-walled cells present on the upper epidermis of grass leaves. They play a crucial role in water conservation and leaf folding/unfolding behavior in response to water availability.
- When bulliform cells are turgid (well-hydrated), they remain swollen, which keeps the leaf surface open and exposed to maximize photosynthesis.
- During water stress, these cells lose water, become plasmolysed, and shrink. This causes the leaf to curl inwards, reducing the surface area exposed to sunlight and minimizing water loss due to transpiration.
Hence, under water stress, the leaf curls inward due to the plasmolysis of bulliform cells. When the cells are turgid again after rehydration, the leaf unfolds and the surface becomes exposed.

Cyclic electron transport involves only PSI and occurs in the stroma lamellae where NADP reductase is absent. It operates efficiently under high light intensity or when ATP demand is high. It does not depend on wavelength below 680 nm; instead, it involves PSI that absorbs light at 700 nm.

Sugar synthesis, also called the Calvin cycle or light-independent reaction, occurs in the stroma of the chloroplast. This process utilizes ATP and NADPH generated in the grana during the light-dependent reactions.

C plants lose less water compared to C plants because their photosynthetic system is more efficient in capturing CO while minimizing water loss. This makes the assertion (A) true, and the reason (R) correctly explains the assertion.

- I. Robert Costanza → Price tags → Nature’s life support services: Costanza is well-known for assigning economic value to ecosystem services, effectively “pricing” them to highlight their role in supporting life.
- II. Sundarbans → Mangroves → Flood protection: The Sundarbans are rich in mangrove forests, which play a key role in protecting coastal areas from flooding and storm surges.
- III. Lichens → Soil formation → Other supporting service: Lichens contribute to weathering of rocks and soil formation, considered a long-term supporting ecological service.
- IV. Ecological function → Public transit → Conserve natural services: Public transit reduces reliance on private vehicles, lowering emissions and contributing to conservation of resources and ecosystem services.

A) Csubscript{4} Photosynthesis — V.S. Rama Das contributed to the study of Csubscript{4} pathway.
B) Plant tissue culture — Shimakura pioneered plant tissue culture techniques.
C) Genetic nature of RNA — Conrat demonstrated RNA as genetic material in TMV.
D) Sexual reproduction in plants — Camerarius was the first to study this in depth.

II) Cauliflower (Pusa Shubra) is resistant to Black rot.
III) Chilli (Pusa Sadabahar) is resistant to TMV.
I) Pusa komal is not related to wheat.
IV) Pusa Swarmin is not resistant to bacterial blight.

- In Engelmann’s experiment:
- A filament of Cladophora was used (I)
- The aerobic bacteria accumulated in red and blue regions indicating maximum O evolution (III)

- II and IV refer to anaerobic studies but are not the key highlights of the original action spectrum experiment.

RUBP regeneration sequence:

(1) VI. Fructose 1,6-bisphosphate (initial product from Calvin cycle)

(2) III. Fructose 6-phosphate (formed after dephosphorylation)

(3) II. Erythrose 4-phosphate (via rearrangements)

(4) IV. Sedoheptulose 7-phosphate (formed through transaldolase action)

(5) V. Ribose 5-phosphate (via carbon rearrangements)

(6) I. Ribulose 5-phosphate (precursor to RUBP)

Let’s analyze the Assertion and Reason:

Assertion (A): Algae increase dissolved oxygen in the environment.

✔️ This is true. Algae perform photosynthesis, releasing oxygen into the water as a byproduct.

Reason (R): Algae form food for aquatic animals.

✔️ This is also true. Algae serve as primary producers and are consumed by organisms like zooplankton and fish.

Does (R) explain (A)?

❌ No. While both statements are factually correct, the reason (R) does not explain the assertion (A). Oxygen production is a result of photosynthesis, not of being a food source.

Conclusion: Both Assertion (A) and Reason (R) are true, but Reason (R) does not explain Assertion (A).

Correct Answer: (2)

Step 1: Understand Calvin Cycle Stoichiometry for 6 CO\textsubscript{2}
The Calvin cycle must run 6 times to produce one molecule of glucose. Each turn fixes one CO\textsubscript{2}.
For 6 CO\textsubscript{2} molecules to enter the cycle:
1. Carboxylation: 6 molecules of Ribulose-1,5-bisphosphate (RuBP, a 5-carbon sugar) combine with 6 molecules of CO\textsubscript{2} to form 12 molecules of 3-Phosphoglycerate (PGA, a 3-carbon compound). 2. Reduction: The 12 molecules of PGA are then reduced to 12 molecules of Glyceraldehyde-3-phosphate (G3P or triose phosphate, a 3-carbon sugar).
3. Regeneration: Out of the 12 G3P molecules, 2 G3P molecules leave the cycle to synthesize glucose or other carbohydrates. The remaining 10 G3P molecules (10 x 3 carbons = 30 carbons) are used to regenerate 6 molecules of RuBP (6 x 5 carbons = 30 carbons) to continue the cycle. Step 2: Focus on the Regeneration Phase Intermediates
The regeneration phase involves a complex series of reactions that interconvert various sugar phosphates. For the regeneration of 6 RuBP from 10 G3P, the key 5-carbon (pentose) sugar phosphate intermediates that are formed and then ultimately converted to Ribulose-5-phosphate (which is then phosphorylated to RuBP) are:
\begin{itemize} \item Xylulose-5-phosphate (Xylulose 5P): Approximately 4 molecules are formed as intermediates. \item Ribose-5-phosphate (Ribose 5P): Approximately 2 molecules are formed as intermediates. \item Ribulose-5-phosphate (Ribulose 5P): All 6 molecules of RuBP are regenerated via the phosphorylation of 6 molecules of Ribulose-5-phosphate. This is the final 5-carbon sugar before it becomes RuBP. \end{itemize} So, for 6 turns of the Calvin cycle, the number of molecules of these key 5-carbon intermediates formed during regeneration are: 4 Xylulose 5P, 2 Ribose 5P, and 6 Ribulose 5P. Step 3: Compare with Options
Let's check the given options against our derived sequence (4 Xylulose 5P, 2 Ribose 5P, 6 Ribulose 5P):
% Option (1) 4 xylulose 5P, 6 Ribulose 5P (Missing Ribose 5P)
% Option (2) 4 xylulose 5P, 2 Ribose 5P, 6 Ribulose 5P (Matches our sequence and numbers)
% Option (3) 2 Ribose 5P, 4 xylulose 5P, 6 Ribulose 5P (Numbers are correct but the order is different, though the question asks for a "sequence" implying the constituents)
% Option (4) 4 xylulose 5P, 2 Ribulose 5P, 2 Ribose 5P (Incorrect numbers for Ribulose 5P and Ribose 5P)
Option (2) provides the correct types and quantities of the 5-carbon molecules involved in the regeneration phase for 6 CO\textsubscript{2} inputs.

I) Correct — Priestley demonstrated the release of O₂ by plants.
II) Incorrect — Ingenhousz proved that oxygen is released in presence of light, not CO₂ release at night.
III) Correct — Sachs demonstrated starch formation in green parts.
IV) Correct — Van Niel explained light-dependent reactions and CO₂ reduction.