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Concept 30.4 Human welfare depends greatly on seed plants
• The absolute dependence of humans on Earth’s flora is a specific and highly refined case of the more general connection between animals and plants. • Like other organisms, we depend on photosynthetic organisms for food production and oxygen release. • However, we use technology to manipulate or select plants that maximize the harvest of plant products for human use. • We rely on seed plants for food, fuel, wood, and medicine. Agriculture is based almost entirely on angiosperms.

• Flowering plants provide nearly all our food.
• Just six crops—wheat, rice, maize, potatoes, cassava, and sweet potatoes—yield 80% of all calories consumed by humans. • Modern crops are the products of a relatively recent burst of genetic change, resulting from artificial selection after the domestication of plants 13,000 years ago. • In maize, key changes such as increased cob size and removal of the hard coating of the kernels may have been initiated by as few as five gene mutations. • How did wild plants change so dramatically so quickly? • The answer is likely a combination of deliberate and unconscious selection for plants with desirable traits, such as large fruits and lack of toxins. • Angiosperms also provide important nonstable foods such as coffee, chocolate, and spices. • Gymnosperms and angiosperms are sources of wood, which is absent in all living seedless plants and consists of an accumulation of tough-walled xylem cells. • Wood is the primary source of fuel for much of the world. • It is used to make paper, and is the world’s most widely used construction material. • Humans depend on seed plants for medicines.

• Most cultures have a tradition of herbal medicine. • Scientific research has identified the relevant secondary compounds in many of these plants, leading to the synthesis of many modern medicines. Plant diversity is a nonrenewable resource.

• Although plants are a renewal resource, plant diversity is not. • The demand for space and natural resources resulting from the exploding human population is extinguishing plant species at an unprecedented rate. • This is especially acute in the tropics, where more than half the human population lives and where population growth rates are highest. • Due primarily to the slash-and-burn clearing of forests for agriculture, tropical forests may be completely eliminated within 25 years. • As the forests disappear, thousand of plant species and the animals that depend on these plants also go extinct. • The destruction of these areas is an irrevocable loss of these nonrenewable resources. • The rate of loss is faster than in any other period, even during the Permian and Cambrian extinctions. • While the loss of species is greatest in the tropics, the threat is global. • In addition to the ethical concerns that many people have concerning the extinction of living forms, there are also practical reasons to be concerned about the loss of plant diversity. • We depend on plants for food, building materials, and medicines. • We have explored the potential uses for only a tiny fraction of the 290,000 known plant species. • Almost all of our food is based on cultivation of only about two dozen species. • Researchers have investigated fewer than 5,000 plant species as potential sources of medicines. • Pharmaceutical companies were led to most of these species by local people who used the plants in preparing their traditional medicines. • The tropical rain forests and other plant communities may be a medicine chest of healing plants that could be extinct before we even know they exist. • We need to view rain forests and other ecosystems as living treasures that we can harvest only at sustainable rates.

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