#Question id: 12084
#Unit 10. Ecological Principles
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.
The best explanation for the increase in nitrate concentration in one treatment is that
#Question id: 7294
#Unit 5. Developmental Biology
Multiple factors regulate flowering in Arabidopsis. FT mRNA is expressed in companion cells of the leaf vein in response to multiple signals, including day length, light quality, and temperature. FT moves in the phloem from leaves to the apical meristem. FT is unloaded from the phloem in the meristem and interacts with FD.
FT-FD complex activates multiple genes. Which of the following combination is correct?(SS)
#Question id: 9176
#Unit 9. Diversity of Life Forms
Wetlands are standing bodies of freshwater, just like lakes and ponds. However, wetlands are different from lakes and ponds because wetlands have ________.
#Question id: 7109
#Unit 5. Developmental Biology
What observation might explain how somites originally become specified to form structures appropriate to their position along the antero-posterior axis?
#Question id: 28836
#Unit 2. Cellular Organization