Pepsin, a common enzyme found in the stomach, is most active at ph values between 0.5 and 2.5. it works slowly between ph values of 2.6 and 3.4. beyond a ph of about 3.5, it becomes completely inactive. why does this happen?
a) the enzyme inactivates because it melts into a liquid when it is not at the right ph.
b) the protein chain in the enzyme is denatured, permanently inactivating it as the ph approaches 7.
c) the enzymes slow down, because changing the ph changes the temperature as well, and affects the reaction.
d) the enzyme's active site contracts into the wrong shape, but this is always reversible if the right ph is restored.

Study the diagram of a cell. which structure is found only in plant cells and functions in the process of photosynthesis? w x y z

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 zone within the open-ocean zone is home to the most organisms? deep zone surface zone intertidal zone transition zone