In bottom sediments of lakes and streams, organic matter is broken down by heterotrophic microorganisms and ammonia is released. Under aerobic conditions, specialized bacteria convert ammonia to nitrate (nitrification). This nitrate, together with nitrate from other sources, diffuses into the deeper sediments, where it may undergo anaerobic conversion to nitrogen gas (denitrification). These sediments typically contain oligochaete worms that live with their heads buried and their tails waving back and forth in the overlying water. Plastic columns were packed with freshly collected  stream  sediments  and  then  covered  with  layers  of  nitrate enriched  water.  A  similar  set  of  columns  was packed with sediment that had been sterilized and then covered with either nitrate-enriched water or distilled water. Oligochaete  worms  were  collected  and  acclimated  to  20°(C)Following  acclimation,  worms  were  rinsed  in  distilled water and then added to three sediment columns. The columns were incubated in the dark at 20°C and monitored every three days for changes in the concentration of nitrate in the overlying water. Nitrate concentrations in each of the experimental treatments were plotted against time, as shown in the graph below.

Which of the following explains why the columns were incubated in the dark?

#Question id: 10206

#Unit 6. System Physiology – Plant

The excess energy is absorbed by three carotenoids molecules such as violaxanthin, antheraxanthin, and zeaxanthin, which of the following statements correct about these molecules?

#Question id: 10207

#Unit 6. System Physiology – Plant

In high light, violaxanthin is converted into zeaxanthin, via the intermediate antheraxanthin by the enzyme known as

#Question id: 10208

#Unit 6. System Physiology – Plant

The large amounts of energy absorbed by the pigments if this energy cannot be stored by photochemistry, this is why a protection mechanism is needed Protection against photodamage is a multilevel process what role does the first line of defense play to suppress from damage?

#Question id: 10209

#Unit 6. System Physiology – Plant

Protection against photodamage is a multilevel process, excited state of chlorophyll is not rapidly quenched by photochemistry it can react with molecular oxygen to form toxic photoproducts such as as singlet oxygen (1 O2*) what can damage if this second line of defense also fails to eliminate the reactive photoproducts?

#Question id: 10210

#Unit 6. System Physiology – Plant

Some xanthophylls also participate in energy dissipation such as in light conversion of Violaxanthin to Zeaxanthin with antheraxanthin as the intermediate and vice-versa, which of the following statements is CORRECT?

a.) The conversion of Violaxanthin to Zeaxanthin a singlet oxygen is removed with the help of co-factor Ascorbate and violaxanthin de-epoxidase under high PPFD

b.) Zeaxanthin is oxidised into violaxanthin with the help of NADPH and oxygen under low PPFD

c.) Conversion of Violaxanthin to Zeaxanthin a singlet oxygen is removed with the help of NADPH and water under low PPFD

d.) Zeaxanthin is oxidised into violaxanthin in presence of enzyme known as violaxanthin de-epoxidase and co-factor Ascorbate under high PPFD

#Question id: 10211

#Unit 6. System Physiology – Plant

Which of the following mechanism is not involve in phtoprotection to plants?