Exploring Reference Points Depending on the reference point you choose, the same object can seem to be
moving or standing still. Furthermore, even if an object seems moving from two
different reference points, observers at those points might disagree about its
speed and direction.

Here is a simple example: In the diagram below, a crow is flying along at a con-
stant speed, carrying a ball. Suddenly, it accidentally drops the ball and watches

it fall. The diagram shows the position of the crow and the ball at five points in
time, one second apart. A person standing still on the ground also watches the
ball fall.

Answer the following questions on a separate sheet of paper.
1. From the reference point of the crow, in what direction is the ball falling? Does
it appear to follow a curved or straight path?
2. How many seconds does it take the ball to fall to the ground?

3. The sides of the grid squares in the diagram are 5 meters long. Using this, cal-
culate the average speed of the ball during its fall from the point of view of the

crow. About how fast was it traveling during the last second of its fall from this
perspective?
4. From the reference point of the person on the ground, does the ball appear to
fall in a straight or curved path?

The dna in a cell’s nucleus encodes proteins that are eventually targeted to every membrane and compartment in the cell, as well as proteins that are targeted for secretion from the cell. for example, consider these two proteins: phosphofructokinase (pfk) is an enzyme that functions in the cytoplasm during glycolysis. insulin, a protein that regulates blood sugar levels, is secreted from specialized pancreatic cells. assume that you can track the cellular locations of these two proteins from the time that translation is complete until the proteins reach their final destinations.for each protein, identify its targeting pathway: the sequence of cellular locations in which the protein is found from when translation is complete until it reaches its final (functional) destination. (note that if an organelle is listed in a pathway, the location implied is inside the organelle, not in the membrane that surrounds the organelle.)

Bisphenol a (often called bpa) is a chemical found in products that people use every day, from water bottles to food containers to children's toys. unfortunately, bpa leaches out of its many products and makes its way into our bodies. what are the health effects of bpa exposure? ongoing research is finding that elevated exposure to bpa can affect a wide variety of developmental and physiological processes, but one of the first studies of bpa's health effects came about because of a simple mistake in the lab. at a laboratory at case western reserve university in 1998, geneticist patricia hunt was making a routine check of her female lab mice. as she extracted and examined developing eggs from the ovaries, she began to wonder what had gone wrong. she noticed that many of the eggs showed problems with their chromosomes, and some had irregular amounts of genetic material, which can lead to miscarriages and birth defects in mammals. she learned that a lab assistant had mistakenly washed the plastic mouse cages and water bottles with a harsh soap, releasing bpa from the plastic. knowing that bpa is an endocrine disruptor, a chemical that can enter organisms and mimic hormones, hunt set out to discover whether it had adversely affected her mice.

Which statement best describes the role of religion and culture in ancient medicine?