SAT or ACT?

Passage III

Ocean depth affects both temperature and dissolved oxygen levels. In Figure 1, the values of temperature, t, in degrees Celsius, and dissolved oxygen, D.O., in milligrams per liter (mg/L), are graphed versus depth, d, in meters below the ocean's surface. Five distinct ocean zones are also identified in Figure 1.

Approximately 989c of marine life is located in the epipelagic, mesopelagic, and bathypelagic zones. Figure 2 shows the percent of marine Me that is located between sea level and a given depth within these three zones. For example, 20% of all marine life is located between sea level and a depth of 50 meters.

Passage IV

Fibromyalgia is a central nervous system disorder characterized by chronic widespread pain and a heightened pain response. Four students each propose a theory of what causes fibromyalgia.

Student 1

Fibromyalgia is caused only by an abnormal immune response to an infection or injury. When the body detects damaged tissue, white blood cells release chemicals called cytokines that direct blood flow to the damaged cells and cause inflammation. The inflammation aggravates the nerves and makes the infected area more sensitive to pain. Usually the increased sensitivity goes away after the inflammation subsides, but sometimes the inflammation causes irreparable physical damage to the nerve cells. Fibromyalgia is the result of the damaged nerve cells disrupting the normal functioning of the central nervous system.

Student 2

Fibromyalgia is caused only by the overproduction of excitatory neurotransmitters. Neurons transmit pain signals by firing chemicals called neurotransmitters that bind to pain receptors on another neuron. The most prevalent of these neurotransmitters is glutamate. When the nerve cells chronically overproduce glutamate, the pain receptors adapt by physically changing shape to more readily absorb the signals. This change makes neurons more sensitive to pain, which results in fibromyalgia. Injury and illness can cause nerve damage to specific neurons, but they do not create the widespread pain of fibromyalgia.

Student 3

Fibromyalgia is caused only by abnormal estrogen or thyroid hormone levels. These hormones affect the production of serotonin and norepinephrine, two inhibitory neurotransmitters that suppress pain transmission through the central nervous system. When levels of these inhibitory neurotransmitters are low, the body is unable to suppress pain transmission, and fibromyalgia is the result. While it is true that some people do overproduce glutamate, sufficient levels of serotonin and norepinephrine neutralize the excess glutamate before it interacts with any pain receptors.

Student 4

Fibromyalgia results only from a diet low in L-tryptophan, an essential amino acid necessary for the production of serotonin. Serotonin helps the brain interpret pain signals. When serotonin levels drop due to inadequate L-tryptophan intake, the brain is unable to properly interpret various pain signals, causing fibromyalgia. Nerve damage from injury only creates localized pain. Excess glutamate is harmless because it is not absorbed by the pain receptors. Estrogen and thyroid hormone imbalances do not limit the production of serotonin.