Pressure potential in the xylem of an actively transpiring plant... | Agrigyan

Analysis of statements:
Statement (A) is correct: Seed dormancy enables viable seeds to survive extended, harsh, or unfavorable periods until appropriate environmental triggers (moisture, temperature, oxygen) signal optimal timing for seedling establishment.
Statement (C) is factually incorrect: Light is definitely not required by all seeds; many agricultural and weed seeds germinate equally well in total darkness, and some are negatively photoblastic (inhibited by light).
Statement (D) is correct: Exogenous physical dormancy is caused by hard, thick, water-impermeable seed coats (e.g., in legumes, Malvaceae) that prevent imbibition of water and exchange of respiratory gases, delaying germination.

Fleshy fruits are categorized into climacteric and non-climacteric types based on their post-harvest respiratory and ethylene response patterns:
Climacteric fruits (e.g., banana, tomato, mango, apple) exhibit a dramatic peak in respiration and an autocatalytic burst of ethylene biosynthesis during ripening. Exogenous ethylene triggers rapid coordinated ripening in these fruits.
Non-climacteric fruits (e.g., grapes, citrus, strawberry, pineapple) do not exhibit autocatalytic ethylene bursts or a climacteric respiratory rise. Their ripening proceeds gradually while attached to the parent vine/plant, and they are essentially insensitive to ethylene-induced post-harvest ripening.

Photorespiration (the $C_2$ photosynthetic carbon oxidation cycle) is a coordinated metabolic pathway compartmentalized sequentially across three distinct organelles:

• Chloroplast: RuBisCO oxygenates RuBP into 3-PGA and 2-phosphoglycolate; the latter is dephosphorylated to glycolate.
• Peroxisome: Glycolate is imported and oxidized to glyoxylate by glycolate oxidase (producing $H_2O_2$, degraded by catalase), and then transaminated to glycine.
• Mitochondria: Two molecules of glycine are converted by glycine decarboxylase and serine hydroxymethyltransferase into one molecule of serine, releasing $CO_2$ and $NH_3$.
  Serine returns to peroxisomes and chloroplasts to regenerate 3-PGA. Vacuoles have no involvement.

Fresh horticultural produce—including leafy vegetables, fleshy fruits, berries, and melons—contains very high water content, typically between 80% and 95% of fresh weight (e.g., lettuce 95%, watermelon 92%, tomato 94%, cucumber 96%). This high moisture content confers crisp turgidity but simultaneously makes fresh produce highly susceptible to desiccation, mechanical damage, rapid post-harvest physiological degradation, and microbial spoilage, giving them a very short shelf-life.