Chapter 15 Notes

Chapter 15 Notes

15.1

People worldwide generally consume the same major nutrients and eat the same basic kinds of food.

But, diets vary by ______.

People in more developed countries tend to eat more food and a larger proportion of proteins and fats than people in less developed countries.

As the human population grows, ______replaces forests and grasslands.

Feeding everyone while maintaining natural ecosystems becomes increasingly difficult.

Different kinds of agriculture have different environmental impacts and different levels of ______.

The efficiency of a given type of agriculture is a measure of the quantity of food produced on a given area of land with limited inputs of energy and resources.

An ideal food crop is one that efficiently produces a large amount of food with little ______impact on the environment.

On average, more energy, water, and land are used to produced a Calorie of food from animals than to produce a Calorie of food from plants.

Animals that are raised for human use are usually fed plant matter, but because less energy is available at each level on a food chain, only about ______percent of the energy from the plants gets stored in the animals.

Thus, a given area of land can usually produce more food for humans when it is used to grow plants than when it is used to raise animals.

The efficiency of raising plants for food is one reason why diets around the world are largely based on plants.

However, ______from animals generally provides more nutrients per gram than most food from plants.

Researchers hope to improve the efficiency of food production by studying plants and other organisms that have high yield.

______is the amount of crops produced per unit area.

Researchers are interested in organisms that can thrive in various climates and that do not require large amounts of fertilizer, pesticides, or fresh water. Some organisms have been a source of food for centuries, while other sources are just being discovered.

Some people become ______because they simply do not get enough food.

More food is needed each year to feed the world’s growing population.

World food production has been increasing for decades, but now food production is not increasing as fast as the human population is increasing.

If all the food in the world today were divided equally among the human population, no one would have quite enough food for good ______.

But food is not divided equally, and malnutrition is largely the result of poverty. Even in the United States, many poor people suffer from malnutrition.

Wars and political strife can also lead to malnutrition because they interrupt transportation systems.

A ______is a prolonged period during which rainfall is below average, and crops grown without irrigation may produce low yields or fail entirely.

A ______is more likely to cause famine in places where most food is grown locally.

If a ______occurs, there may be no seed to plant crops the following year. The effects of a drought can continue for years.

People in a given area can usually survive one crop failure. They may have saved enough food from previous seasons, or they may have systems for importing food from elsewhere.

But several years of drought cause severe problems for any area of the world.

For example, after a long drought, the soil may be less able to support the production of food crops.

Worldwide, between ______and 1970, increases in crop yields resulted from the use of new crop varieties and the application of modern agriculture techniques.

These changes were called the green revolution. Since the 1950s, the green revolution has changed the lives of millions of people.

However, the ______revolution also had some negative effects.

For example, most new varieties of grain produce large yields only if they receive large amounts of water______, and pesticides. In addition, the machinery, irrigation, and chemicals required by new crop varieties can degrade the soil if they are not used properly.

As a result of the overuse of fertilizers and pesticides, yields from green revolution crops are falling. The grain production in the U.S. has decreased since 1990, partly because the amount of water used for irrigation has decreased.

In addition, the green revolution had a negative impact on subsistence farmers, or farmers who grow only enough food for local use.

Before the green revolution, ______farmers worked most of the world’s farms.

But they could not afford the equipment, water, and chemicals needed to grow new crop varieties.

15.2

______land is farmland that can be used to grow crops.

The Earth has only a limited area of arable land.

But, as the human population continues to grow, the amount of arable land per person decreases.

The basic processes of farming include ______, ______, irrigation, and pest control.

Traditionally, plows are pushed by the farmers or pulled by ______. Plowing helps crops grow by mixing soil nutrients, loosening soil particles, and uprooting weeds. Organic fertilizers, such as manure, are used to enrich soil. While fields are irrigated by water flowing through ditches.

These traditional techniques have been used since the earliest days of farming.

In most ______countries, the basic processes of farming are now carried out using modern agricultural methods.

Machinery powered by fossil fuels is now used to plow the soil and harvest crops. Synthetic chemical fertilizers have replaced manure and plant wastes to fertilize soil.

A variety of overhead sprinklers and drip systems may be used for irrigation. And synthetic chemicals are used to kill pests.

Soil that can support the growth of healthy plants is called ______soil.

______is the surface layer of the soil, which is usually richer in organic matter than the subsoil is.

______topsoil is composed of living organisms, rock particles, water, air, and organic matter, such as dead or decomposing organisms. Several layers of soil lie under the topsoil. The bottom layer is bedrock, which is the solid rock from which most soil originally forms.

Most soil forms when rock is broken down into smaller and smaller fragments by wind, water, and chemical weathering. ______weathering happens when the minerals in rock react chemically with substances to form new materials. Temperature changes and moisture can also cause rock to crack and break apart.

It can take hundreds or even thousands of years for these geological processes to form a few centimeters of soil.

Other processes also help to produce fertile topsoil. For example, the rock particles supply mineral nutrients to the soil.

______and bacteria live in the soil, and they decompose dead plants as well as organic debris and add more nutrients to the soil.

Earthworms, insects, and other small animals help plants grow by breaking up the soil and allowing air and water into it.

______is a process in which the materials of the Earth’s surface are loosened, dissolved, or worn away and transported from one place to another by a natural agent, such as wind, water, ice, or gravity.

In the U.S., about half of the original topsoil has been lost to erosion in the past 200 years.

Without topsoil, crops cannot be grown. Yet, almost all farming methods increase the rate of soil erosion.

Land degradation happens when human activity or natural processes damage the land so that it can no longer support the local ecosystem. In areas with dry climates, desertification can occur.

______is the process by which human activities or climatic changes make arid or semiarid areas more ______.

This process is causing some of our arable land to disappear.

For example, in the past, people who lived in the drier part of the Sahel region in Africa grazed animals, while people in the wetter part of the region planted crops.The grazing animals were moved from place to place to find fresh grass. The cropland was planted for only a few years, and then allowed to lie fallow, or to remain unplanted, for several years.

These methods allowed the land to adequately support the people in the Sahel.

But the population in the region has grown, and the land is being farmed, grazed, and deforested faster than it can regenerate. Crops are planted too frequently and fallow periods are being shortened or eliminated completely.

As a result, the soil is losing fertility and productivity. Because of overgrazing, the land has fewer plants to hold the topsoil in place.

So, large areas have become desert and can no longer produce food.

There are many ways of protecting and managing topsoil and reducing erosion.

Soil usually erodes ______, and many soil conservation methods are designed to prevent downhill erosion.

For example, soil-retaining terraces can be build across a hillside. On gentler slopes, contour plowing, which consists of plowing across the slope of a hill instead of up and down the slope, can be used.

An even more effective method of plowing is leaving strips of vegetation across the hillside instead of plowing the entire slope.

These strips catch soil and water that run down the hill.

Still, many areas of land that have hills are not suited to farming, but may be better used as forest or grazing land.

In ______farming, a crop is harvested without turning the soil over, as in traditional farming.

Later, the seeds of the next crop are planted among the remains of the previous crop. The remains of the first crop hold the soil in place while the new crop develops.

Although this method saves time and reduces soil erosion, it is not suited for all crops. Other disadvantages include soil that is too densely packed and lower crop yields over time.

Soil was traditionally fertilized by adding organic matter that would decompose, adding nutrients to the soil and improving the soil texture.

However, ______fertilizers that contain nitrogen, phosphorous, and potassium have changed farming methods. Without them, world food production would be less than half of what it is today.

If erosion occurs in areas fertilized with inorganic materials, waterways may become polluted.

Over the past 50 years, the use of such inorganic fertilizers has increased rapidly.

A modern method of enhancing the soil is to use both organic and inorganic materials by adding compost and chemical fertilizers to the soil.

______is a mixture of decomposing organic matter, such as manure and rotting plants, that is used as fertilizer and soil conditioner.

Many cities and industries now compost yard and crop wastes. This compost is then sold to farmers and gardeners, and the process is saving costly land fill space.

The accumulation of salts in the soil is known as ______.

______is a major problem in places that have low rainfall and naturally salty soil.

When water evaporates from irrigated land, salts are left behind.

______can be slowed if irrigation canals are lined to prevent water from seeping into the soil, or if the soil is watered heavily to wash out salts.

Worldwide, pests destroy about one-third of the world’s potential food harvest.

A ______is any organism that occurs where it is not wanted or that occurs in large enough numbers to cause economic damage.

Humans try to control populations of many types of pests, including plants, fungi, insects, and microorganisms.

Many farmers rely on pesticides to produce their crops.

A pesticide is a poison used to destroy pests, such as insects, rodents, or weeds; examples include insecticides, rodenticides, and herbicides.

Pesticides, however, can also harm beneficial plants and insects, wildlife, and even people.

Over time, spraying large amounts of pesticide to get rid of pests usually makes the pest problem worse.

Pest populations may evolve resistance, the ability to survive exposure to a particular pesticide.

More than 500 species of insects have developed resistance to pesticides since the 1940s.

Pesticides are designed to kill organisms, so they may also be dangerous to humans.

Cancer rates among children in areas where large amounts of pesticides are used on crops are sometimes higher than the national average.

People who apply pesticides need to follow safety guidelines to protect themselves from contact with these chemicals.

The problem of pesticides harming people and other organisms is especially serious with pesticides that are persistent.

A pesticide is ______if it does not break down easily or quickly in the environment.

______pesticides do not break down into harmless chemicals, and they accumulate in the water and soil.

Some pesticides have been banned in the United States for decades but can still be detected in the environment.

Biological pest control is the use of certain organisms by humans to eliminate or control pests.

Every pest has enemies in the wild, and these enemies can sometimes be used to control pest populations.

Biological pest control includes the use of

-______,

-plant defenses,

-______,

-and the disrupting of insect breeding

______pest management is a modern method of controlling pests on crops.

The goal of integrated pest management is not to eliminate pest populations but to reduce pest damage to a level that causes minimal economic damage.

Such programs can include a mix of farming methods, biological pest control, and chemical pest control.

Biological methods are the first methods used to control the pest. So, natural predators, pathogens, and parasites of the pest may be introduced.

Cultivation controls, such as vacuuming insects off the plants, can also be used.

As a last resort, small amounts of insecticides may be used. These insecticides are changed over time to reduce the ability of pests to evolve resistance.

______engineering is a technology in which the genome of a living cell is modified for medical or industrial use.

Scientists may use genetic engineering to transfer desirable traits, such as resistance to certain pests, from one organism to another.

Plants that result from genetic engineering are called ______(GM) plants.

In the United States, we now eat and use genetically engineered agricultural products everyday.

Many of these products, however, have not been fully tested for their environmental impacts.

Some scientists warn that these products will cause problems in the future.

Farming that conserves natural resources and helps keep the land productive indefinitely is called sustainable agriculture.

Sustainable agriculture involves planting productive, pest-resistant crop varieties that require little energy, pesticides, fertilizer, and water.

15.3

Food from animals has been the basis of life for some human populations for centuries.

Our ancestors obtained animal protein by hunting and fishing. Today, most people get animal protein from domesticated species.

______describes organisms that have been bred and managed for human use.

Because fish are an important food source for humans, the harvesting of fish has become an important industry worldwide.

However, when too many fish are harvested over a long period of time, ecological systems can be damaged.

______is the catching or removing from a population more organisms than the population can replace.

Many governments are now trying to stop overharvesting. They have created no-fishing zones, so that fish populations can recover.

Aquaculture is the raising of aquatic plants and animals for human use or consumption.

Fish and other aquatic organisms provide up to 20 percent of the animal protein consumed worldwide.

Aquaculture may be one solution to the overharvesting of fish and other organisms
in the world’s oceans.

Aquaculture is not a new idea.

This practice probably began in China about 4,000 years ago.

Today, China leads the world in using aquaculture to produce freshwater fish.

There are a number of different methods of aquaculture. Among these are

Fish ______

Fish ______

Fish farms generally consist of many individual ponds that each contain fish at a specific stage of development. Fish grow to maturity in the ponds and are then harvested.

Fish ranches raise fish to a certain age, release them to the ocean, and then harvest the adults when they return to their birthplace to breed.

As with other methods of food production, however, aquaculture can cause environmental damage if not managed properly.

Aquatic organisms can produce a large amount of waste, which can be a source of pollution.

Because aquaculture requires so much water, the process can deplete local water supplies.

Despite these problems, aquaculture will continue to be an important source of protein for the human
diet.

______is the term given to domesticated animals that are raised to be used on a farm or ranch or to be sold for profit.

Populations of livestock have changed dramatically in the last 40 years.

Large livestock operations produce most of the meat that is consumed in developed countries.

In ______countries, livestock not only provide leather, wool, eggs, and meat, but also serve other functions.

Some livestock are used as draft animals to pull carts and plows.

Other livestock provide manure as the main source of plant fertilizer or as a fuel for cooking.

Ruminants are cud-chewing mammals that have a three- or four-chambered stomach.

Cattle, sheep, and goats are examples of ______.

______is the food that these animals regurgitate from the first chamber of their stomachs and chew again to aid digestion.

When we eat the meat of ruminants, we are using them to convert plant material, such as grass stems and woody shrubs, into food that we can digest—such as beef.