Question

If a starving plant is provided with glucose, the rate of respiration
(a)Falls first then rises
(b)Becomes constant
(c)First rises then falls
(d)Increase

Answer 1

Hint: The lower respiration rate is caused due to a deficit of the respiratory substrate rather than by mitochondrial degradation. The sugar content declines as a result of limited photosynthesis thus, the senescence may be induced by sugar starvation.

Complete answer:
Under sugar starvation, the increased utilization of cytosolic proteins and storage protein is accompanied by more intensive catabolism of lipids aimed to supply respiratory substrates. In turn, sugar feeding significantly retards the breakdown of storage lipids. The stomatal closure minimizes hydraulic failure during saturation periods which causes low photosynthetic carbon intake. When starving plants when provided with glucose, when provided with glucose shows, rises in the rate of respiration as glucose content is maximum but decreases with the decrease in glucose content.

Additional Information:
-During sugar starvation of a plant, there are three-phase can be distinguished:
Phase I-Acclimation Phase: The phase when carbohydrate levels and respiration decrease with the nitrogen released from storage proteins through their degradation.
Phase II-Survival Phase: This phase involves the intensive breakdown of protein and lipids, releasing free amino acid. This phase can be reversed by sugar feeding.changes are irreversible.
Phase III-Cell Organization Phase: This phase marked by all metabolites and enzymatic activity is decreed.

So, the correct answer is ‘the first rise then fall.’

Note: -During sugar starvation, the respiration rate declines rapidly in embryos of garden pea and yellow lupine.
-Glucose is a useful product. Some glucose is used straight away by the plant cells, some are converted to starch for storage and later used for food.
-During sugar starvation at the acclimation and survival phases, the total protein content decreases which are associated with a temporary increase in free amino acid and an increase in proteolytic activity.