N 2000, Bob Harmon discovered the best-preserved Tyrannosaurus rex skeleton ever found. The fossilized dinosaur was sticking out of the wall of a canyon in Montana. Many scientists were eager to study the fossils. Dr. Mary Schweitzer got one of the leg bones to analyze. Dr. Schweitzer’s assistant dissolved the bones in acid and discovered that some soft tissue had survived even after 68 million years. The discovery was a shock to the scientific community. No one had ever found such old tissues.

Before laying eggs, female birds store calcium inside their bones that they will need to make eggshells. This layer of bone is called medullary bone. In the T. rex leg bone, Dr. Schweitzer found tissue just like the medullary bone of birds. The dinosaur was a female! If Dr. Schweitzer’s hypothesis is right, she is the first scientist to identify the sex of a T. rex. Which organ system includes the bones?

A. skeletal system
B. muscular system
C. reproductive system
D. integumentary system

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.