Chap. 9. The Biosphere 233is that some toxic substances may mimic the action of hormones. For example, evidence
exists to suggest that premature sexual development in some young female children can
be caused by ingestion of synthetic chemicals that mimic the action of the female sex
hormone estrogen.
9.5. Reproduction and Inherited Traits
As noted in the preceding section, one of the major activities of organisms is
metabolism by which organisms process materials and energy. The other major activity of
all organisms is reproduction. Most organisms are capable of reproducing a large excess
of their species because throughout time predators and hostile conditions have required
large numbers of juveniles to ensure survival of enough members to continue the species.
Unrestrained reproduction, especially by humans, poses a strong threat of overpopulation
and is a major concern related to reproduction and the environment. A second major
concern is the potential effect of environmental chemicals upon reproduction and the
potential that such chemicals have to cause birth defects. Therefore, chemicals that may
affect reproduction are given strong consideration in the practice of green chemistry.
Primitive single-celled organisms, particularly bacteria, undergo asexual reproduction
in which a cell simply splits to form two cells. Humans and most other multicelled
organisms undergo sexual reproduction requiring that male sperm cells fertilize female
egg cells to produce cells capable of dividing and producing new individuals.
Reproduction is directed by genes which occur in molecules of deoxyribonucleic
acid, DNA, discussed in Chapter 5, Section 5.5. The DNA of an individual, which
in sexual reproduction has contributions from both parents, determines the physical,
biochemical, and behavioral traits of the organism. The DNA can be altered resulting in
changes called mutations. A miniscule fraction of mutations are desirable and convey
advantages to an individual that are passed along as heritable characteristics in offspring.
This is the process of natural selection that has resulted in literally millions of different
species of organisms.
Some chemicals are capable of producing mutations. Control of production and
exposure to these mutagens is a major thrust of green chemistry. This is particularly
so because substances that cause mutations are generally regarded as being capable of
causing cancer as well.
9.6. Stability and Equilibrium of the Biosphere
In order for an organism to survive and thrive, it must reach a state of stability and
equilibrium with its environment. The term given to such a state is homeostasis (“same
status”). In maintaining homeostasis, an organism must interact with its surroundings
and other organisms in its surroundings and must balance flows and processing of matter
(including nutrients) and energy. On an individual basis, organisms do a remarkably
good job of keeping their internal levels of water, materials such as calcium in blood,
and temperature within a range conducive to their well being. Mammals have developed
extraordinary capabilities of homeostasis; a healthy individual maintains its internal