To investigate the possible presence of introns in three newly discovered genes (X, Y, and Z), you perform an experiment in which the restriction enzyme HaeIII is used to cleave either the DNA of each gene or the cDNA made by copying its mRNA with reverse transcriptase. The resulting DNA fragments are separated by gel electrophoresis, and the presence of fragments in the gels is detected by hybridizing to a radioactive DNA probe made by copying the intact gene with DNA polymerase in the presence of radioactive substrates. The following results are obtained: Source of DNA Number of Fragments After Electrophoresis Gene X DNA 3 cDNA made from mRNA X 2 Gene Y DNA 4 cDNA made from mRNA Y 2 Gene Z DNA 2 cDNA made from mRNA Z 2 Part A What can you conclude about the number of introns present in gene X

One statements is an example of a scientific observation. another statement is an example of a scientific explanation. identify the correct statement for each category to illustrate how scientific explanations are inferred from scientific observations.

Consider the motion of the balloon and its air contents in terms of momentum. in step 1 above, the total momentum of the balloon and its contents was zero. recall that momentum = mv. both the balloon and the air inside it had a velocity of zero and therefore the total momentum was zero. now think about what happened when the air escaped from the balloon. a certain mass of air accelerated in one direction. in order to keep the total momentum of the system zero, the balloon itself (which has mass) had to accelerate in the opposite direction. use this scenario to you explain why the soda can rotates when the water squirts out of the escape holes. what was your hypothesis concerning the water-filled can? according to your data, do you think your hypothesis was correct? (be sure to refer to your data when answering this question.) summarize any difficulties or problems you had in performing the experiment that might have affected the results. describe how you might change the procedure to avoid these problems. give at least one more example of newton's third law in everyday life.

Why do we perceive objects as retaining their brightness under different lighting levels?