In subarctic saltmarshes, scientists have found that the addition of calcium has no effect on productivity, but additional iron does increase productivity. In this example, iron
A. is a precursor to calcium.
B. stimulates evapotranspiration.
C. biomagnifies in the marsh plants.
D. is a limiting factor.
E. blocks the effect of calcium.
D. is a limiting factor.
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How many times must each of the reactions in the Calvin cycle take place in order to
A. 6 B. 3 C. 2 D. 1
Rock layers right at the K-Pg boundary have enriched concentrations of the element iridium. This is significant for understanding the mass extinction that happened at the time, because ________
A) iridium is toxic to life and could have killed off many species B) iridium is very rare in the Earth's crust but relatively common in meteorites C) iridium forms under conditions of extreme shock and heat D) iridium would have caused an episode of severe acid rain E) iridium-rich dust is particularly effective at blocking incoming solar radiation
Photosynthesis occurs in the chloroplasts of cells and cell respiration occurs in the mitochondria. Plants undergo both reactions.
A. true B. false
Which of the following internal structures of the eukaryotic cell could be considered important in the cellular defense?
A) ?lipid bilayers B) ?mitochondria C) ?lysosomes and peroxisomes D) ?purines and pyrimidines