An experiment was designed to investigate the effect of caffeine on the rate of heartbeat of fruit flies. Two populations of fruit flies were grown in a lab. Both
populations were raised drinking the same water and the same type of food. Both
populations were exposed to the same amount of light and temperature at 20
degrees Celsius. The fruit flies' heartbeats were then monitored at two hour
intervals. The fruit flies of population one were given caffeine five minutes before
their heartbeat was checked. The flies of population two were not given any
caffeine.
Which of the following is a controlled variable in this experiment?
temperature
caffeine
heart rate
experimental group

Which of the following is a possible reason for sleep? a) growth b)digestive c)speed d)intelligence

Spring tides, when the high tides are at their highest and low tides at their lowest. what is it about these positions that causes these high and low tides?

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.