Ateam of scientists visits an island in the caribbean sea. they find a diverse community of turtles, lizards, birds, and a variety of trees, shrubs, and grasses. no humans live on the island. several years later, the scientists return to the island. they find a much smaller community, with reduced populations of all of the species they had identified earlier. some of the animals now appear to be absent from the island. which is the most likely explanation for the changes that the scientists observed? a. competition for resources caused all of the island populations to decrease at the same time. b. a disease or parasite affected all of the island populations. c. a natural disaster, such as a hurricane, struck the island. d. stress from overcrowding affected all of the island populations.

Despite the differences in mature plant cells, all of them are derived from meristem cells. the three major types of tissue systems develop from the meristem. meristems develop cells in all but which tissue?

Rease is an enzyme used by plants to break down urea (a nitrogen-containing compound) into carbon dioxide and ammonia. urease urea > > > carbon dioxide and ammonia ammonia is broken down by plants into a nitrogen source plants need to grow. thus, plants could not use urea as a nitrogen source unless it was first converted to ammonia. in soybean plants there are two different kinds of urease, one produced in the seeds and the other produced in the leaves of the plant. three types of soybean plants were used in a set of experiments: normal soybeans and two mutant strains, one lacking the urease in the seeds only (strain 1) and one lacking urease in the leaves only (strain 2). experiment 1 separate areas in a field were planted with normal, strain 1, and strain 2 soybeans. all types of soybeans appeared to grow, flower, and produce seeds equally well. there were no externally detectable differences among the strains. experiment 2 small pieces of plant leaves of equal weight were obtained from each type of soybean plant and separately placed on media in culture dishes. tissue growing in this way will become an unorganized clump of cells referred to as callus. to provide a controlled nitrogen source, half the tissue samples of each type were placed on media containing urea, and the other half of the samples were placed on media containing ammonia. after 30 days, the weight gain for each of the callus samples was determined. results are shown in the table below.

20 the compound al(nh3)2 has atoms of nitrogen.