Page 306 - ABCTE Study Guide_Neat

Question

AIDS is such a difficult disease to treat because

A it is a virus.

B we don’t know how it attacks the body.

C it compromises the cells that should attack it.

D it is undetectable by the body’s immune response.

Answer

The answer is C. Since the HIV virus attacks T cells, it is occupying the cells that should be attacking the
disease, thus compromising the whole immune response.

Natural Cycles

Lesson Objective

In the coming pages, we’ll examine several different natural cycles and see how they work in concert to
promote and preserve life.

When functioning properly, the environment and ecosystem cycle vital nutrients and energy, providing a
renewable supply of necessary products and services. Many of the processes are very complex, with subtle
background processes and interactions not readily apparent but highly important to the functioning of the
system. Let’s review some of the most important ones.

Previously Covered

In the preceding section, we reviewed some of the body’s defenses and examined the different systems of
the body and their specific functions. We also brushed up on how cells divide in order to grow and heal
the body.

The Hydrologic Cycle

The water, or hydrologic, cycle is essential to life on earth, especially that of land animals including
humans. Energy from the sun drives the process, through evaporation from oceans and surface water,
photosynthesis in plants, and transpiration of water into the atmosphere. Because of the tilt of the earth’s
axis, surface water and air are not heated evenly, resulting in seasons, major ocean currents, and
weather phenomena such as clouds, wind, and precipitation.

As warm, moisture-laden air rises into the atmosphere, it is cooled and then falls back to earth as
precipitation capable of replenishing ground and surface water supplies. Some returns to the oceans.
Large areas of plant life, such as the tropical rain forests, are integral in transpiring water into the
atmosphere and supplying much of the moisture needed for the rainfall that occurs at the tropical
latitudes.

Water helps carry nutrients through ecosystems as it filters through soil and rock. If too much water filters
through soil and rock, it can cause soil erosion or the removal of vegetation by wind or water. Soil