#Question id: 18747
#Unit 13. Methods in Biology
#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: 1818
#Unit 4. Cell Communication and Cell Signaling
Which of the following is the single best defining molecule on, or in, a B-cell?
#Question id: 24611
#Unit 2. Cellular Organization
#Question id: 30118
#Unit 1. Molecules and their Interaction Relevant to Biology