troop Agroup of lemurs, monkeys, apes, or other
primates.
trophallaxis The mutual exchange of alimentary liq-
uid among colony members, such as between adult and
larvae of certain social insects, e.g., ants, bees, or
wasps.
trophic level Serves as a way to delineate levels on
the food chain from producers to consumers. Some
organisms like humans are multitrophic.
trophic structure The distribution of the energy
flow and its relationships through the various trophic
levels.
trophoblast The outer layer of epithelium of the
blastocyst that gives rise to the mammalian placenta
and in which the embryo receives nourishment from
the mother. The trophoblast differentiates into the syn-
cytiotrophoblasts, the outer large cell layer that pro-
duces HCG (human chorionic gonadotropin) that
stimulates the production of estrogen and progesterone
within the ovary, and cytotrophoblast, the compacted
cell inner layer next to the mesoderm. The trophoblast
attaches itself to the uterus wall in a process called
implantation and goes on to become the various life
support systems (placenta, amniotic sac, umbilical
cord), while the blastocyst develops into the embryo.
tropical rain forest A warm, moist terrestrial biome
with a tree canopy. Two types of rain forest exist, the
temperate and the tropical. Tropical rain forests are
found close to the equator, while temperate rain forests
are found near coastal areas, such as the American
Pacific Northwest stretching from Oregon to Alaska for
1,200 miles. Characteristics of rain forests are trees that
flareat the base, with very dense vegetation that is tall
and green and rich in animal species. Both types receive
lots of rain, with the tropical rain forest obtaining 400
inches a year, while the temperate rain forest receives
about 100 inches per year. Tropical rain forests are
warm and moist, but temperate rain forests are cool.
Tropical rain forests lie between the tropic of Cancer
and the tropic of Capricorn and receive rainfall regularly
throughout the year (80–400 inches per year) and are
warm and frost free all year long (mean temperatures
are between 70 and 85°F), with very little daily fluctua-
tion. Tropical rain forests are found in Latin America
(57 percent), while one-third of the world’s tropical rain
forests are in Brazil. Some 25 percent of the tropical rain
forests can be found in Southeast Asia and the Pacific
Islands, and 18 percent are found in West Africa.
Smaller temperate rain forests can be found on the
southeast coast of Chile in South America and a few
other coastal strips, including small areas in the United
Kingdom, Norway, Japan, New Zealand, and southern
Australia.
Half of the world’s plant and animal species live in
the tropical rain forests, even though they comprise
only 20 percent of all forests. These richly diverse
ecosystems are being destroyed at a rate of 30 acres of
trees being cut every minute.tropic hormone Hormones that cause secretion of
other hormones.tropism The movement of a plant toward (positive
tropism) or away (negative tropism) from an environ-
mental stimulus by elongating cells at different rates.
Phototropism is induced by light; gravitropism is
induced by gravitational pull; hydrotropism is a
response to water gradients; and thigmotropism is a
response to touch.tsetse flies Vectors of African trypanosomiasis, caus-
ing nagana in livestock, a fatal disease of horses and
cattle, and sleeping sickness in humans. Members of the
Glossinidae; there are 23 species and eight subspecies.
The simple proboscis of tsetse flies projects straight out
front from the head, consisting only of labrum,
hypopharynx, and labium. Found only in sub-Saharan
Africa and two localities in the Arabian Peninsula.tuber A short, swelled or enlarged, fleshy under-
ground part of a stem or root used as food storage by
the plant, e.g., potato.330 troop