Giardia intestinalis can cause disease in several different mammalian species, including humans. Giardia organisms (G. intestinalis) that infect humans are similar morphologically to those that infect other mammals, thus they have been considered a single species. However, G. intestinalis has been divided into different subgroups based on their host and a few other characteristics. In 1999, a DNA sequence comparison study tested the hypothesis that these subgroups actually constitute different species. The following phylogenetic tree was constructed from the sequence comparison of rRNA from several subgroups of G. intestinalis and a few other morphologically distinct species of Giardia. The researchers concluded that the subgroups of Giardia are sufficiently different from one another genetically that they could be considered different species.

According to the phylogenetic tree in the figure above, G. intestinalis constitutes a ________ group.

#Question id: 12098

#Unit 10. Ecological Principles

The herbaceous plant Achillea lanulosa is widespread in the Northern Hemisphere. Phenotypic variation in the species has been extensively studied along an altitudinal gradient from sea level to over 3,000 meters. In California there is conspicuous variation in  height; alpine plants are only several centimeters tall  while  those in  the San Joaquin Valley may reach a height of 1.8 meters. Adaptation to different local environments also results in variation in physiological processes such as photosynthetic rate, resistance to cold, and the timing of dormancy.

The morphological variation shown by Achillea lanulosa illustrates

#Question id: 2177

#Unit 2. Cellular Organization

 The resting membrane potential in animal cells depends largely on nongated _____ channels.

#Question id: 20052

#Unit 13. Methods in Biology

#Question id: 4049

#Unit 3. Fundamental Processes

Which of the following are products of RNA polymerase II activity?

A. tRNA ___

B. microRNA ___

C. hnRNA ___

D. tRNA and microRNA ___

#Question id: 11032

#Unit 7. System Physiology – Animal

An electrocardiogram (ECG) provides information about ________.