Of carbon dioxide that was in the atmosphere in prehistoric times. Scientists retrieved this data from air bubbles trapped in ancient ice in Vostok, Antarctica.
Carbon dioxide levels are provided in parts per million (ppm).
400
375
Graph 1: Atmospheric Carbon Dioxide BCE
(www. co2.earth)
350
325
300
Atmospheric Carbon Dioxide Levels
275
250
225
ws
200
175
400,000
300,000
100,000
200.000
Years Before Present
3. What time frame does this graph include?*
1 point
O a. about 400,000 years ago to the present
O b. from the present day to 400,000 years in the future
O c. one million years ago to the present day
O d. the graph does not provide a timeframe

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.