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Transcript
Section 1
Feeding the World
Objectives
In 2011, lack of rain, loss of soil, and war caused crops to fail in Somalia. This
catastrophic combination resulted in famine, which is widespread starvation
caused by a shortage of food. Events like the famine in Somalia present a
frightening picture of the difficulty of feeding Earth’s growing population. By 2050,
the world’s farmers will need to feed about 9 billion people. In this chapter, you
will learn why feeding all the world’s people a nutritious diet is difficult, and how
food production can be increased without irreversibly damaging the environment.
Identify the major causes
of malnutrition.
Compare the environmental
costs of producing different
types of food.
Explain how poverty is a major
cause of malnutrition.
Explain the importance of the
green revolution.
Humans and Nutrition
The human body uses food both as a source of energy and as a source
of materials for building and maintaining body tissues. The amount
of ­energy that is available in food is expressed in Calories. One Calorie
(Cal) is equal to 1,000 calories, or one kilocalorie. As shown in Figure 1.1,
the ­major nutrients we get from food are carbohydrates, proteins, and
lipids. Our bodies need smaller amounts of vitamins and minerals to
stay healthy.
Connect to BIOLOGY
Key Terms
famine
malnutrition
diet
yield
Malnutrition is a condition that occurs when people do not consume
enough Calories or do not eat a sufficient variety of foods to fulfill all of
the body’s needs. There are many forms of malnutrition. For example,
­humans need to get eight essential amino acids from proteins. This is
easily done if a variety of foods are eaten. However, in some parts of the
world, the only sources of food may be corn or rice. Both corn and rice
contain proteins, but they lack some essential amino acids, vitamins,
and minerals. Protein-energy malnutrition results, affecting the normal
physical and mental development of children.
Connect to BIOLOGY
Figure 1.1
Major Nutrients in Human Foods
Essential Amino Acids
Nutrient
Composition
Sources
Energy yield
Function
Carbohydrates
sugars
wheat, corn,
and rice
4 Cal/g
is the main
source of the
body’s energy
Lipids (oils and fatty acids and
fats)
fatty alcohols
olives, nuts,
9 Cal/g
and animal fats
helps form
membranes
and hormones
Proteins
animal food
and smaller
amounts from
plants
helps build
and maintain
all body
structures
amino acids
about 4 Cal/g
Animals make their own proteins from
amino acids. Essential amino acids
are those that must be supplied in the
diet because the body needs them but
cannot make them from other amino
acids. A lack of essential amino acids in
the diet can lead to the human diseases
kwashiorkor and marasmus, which can
cause brain damage in children.
Chapter 15: Food and Agriculture
379
Figure 1.2
World Food Production This bar graph shows that in 2009, more grains (wheat, corn, and rice) were
produced than any other food. Wheat and corn are eaten by humans and are fed to farm animals.
World Food Production, 2009
Wheat
Corn
Rice
Potatoes
Soybeans
Beans
Fish
Beef
Pork
Poultry
0
100
200
300
400
500
600
700
800
900
Metric tons (in millions)
Source: UN Food and Agriculture Organization
Sources of Nutrition
A person’s diet is the type and amount of food that he or she eats.
A healthy diet is one that maintains a balance of the right amounts
of ­nutrients, minerals, and vitamins. In most parts of the world, people
eat large amounts of food that is high in carbohydrates, such as rice,
­potatoes, and bread. As shown in Figure 1.2, the foods produced in the
greatest amounts worldwide are grains, which are plants of the grass
family whose seeds are rich in carbohydrates. Besides eating grains, most
people eat fruits, vegetables, and smaller amounts of meats, nuts, and
other foods that are rich in fats and proteins.
Diets Around the World
Figure 1.3
Total Calorie Supply People in
developed countries generally eat more
food and more proteins and fats than
people in less developed countries eat.
World
Least developed
countries
North America
People worldwide generally consume the same major nutrients and eat
the same basic kinds of food. But diets vary by geographic region, as
shown in Figure 1.3. People in more-developed countries tend to eat more
food and a larger proportion of proteins and fats than people eat in lessdeveloped countries. For example, in the United States, almost half of all
Calories people consume come from meat, fish, and oil.
Total Calorie Supply, per Person, per Day
Food Supply
(kcal/capita/day)
Proteins (g/capital/day)
Fats (g/capita/day)
Europe
Asia
Africa
0
500
1,000
1,500
2,000
Total Calories
380
Unit 4: Water, Air, and Land
2,500
3,000
3,500
4,000
Source: UN Food and Agricultural Organization
The Ecology of Food
Connect to MATH
As the human population grows, farmland and suburbs replace forests
and grasslands. Feeding everyone while maintaining natural ecosystems
becomes more difficult. Different kinds of agriculture have different
­environmental impacts and different levels of efficiency.
Food Efficiency
The efficiency of a given type of agriculture is a measure of the q
­ uantity
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 negative impact on the environment.
Extra Calories
An active man who weighs 70 kg
main­tains his weight if he eats 2,700
Cal per day. Unused Calories are
converted into stored fat at the rate
of 1 kg of fat per 9,000 Cal that are
unused. If this active man consumes
3,600 Cal per day, how much weight
does he gain each year?
On average, much more energy, water, and land are needed to produce 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. Because less energy is available at each higher level on a food
chain, only about 10 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, meat generally
provides more nutrients per gram than does most food from plants.
Old and New Foods
Researchers hope to improve the efficiency of food production by
­studying plants and other organisms that have high yield—the amount
of food that can be produced in a given 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, as shown in Figure 1.4.
Figure 1.4
(br) ©WILDLIFE GmbH/Alamy Images; (bl) ©Chris Hellier/Corbis
Food Sources Marine algae, or seaweeds, (left) have been harvested and eaten by humans for centuries. Glasswort
(right) is a salad green that may become an important food source in the future because it can grow in salty soil.
Chapter 15: Food and Agriculture
381
Figure 1.5
Lack of Resources Refugees in
Somalia wait in line for food assistance.
World Food Problems
The world’s farmers produce enough grain to feed up to 10 billion people
an adequate vegetarian diet. However, no one is satisfied with eating just
the minimal amount of food needed for survival. And, many of us consume about a third of our Calories from animals, not grain.
Poverty and Violence
Check for Understanding
Summarize What could be done to
increase the productivity of the land
worked by subsistence farmers?
Malnutrition today is largely a result of poverty and violence, as indicated
in Figure 1.5. In 2010, the United Nations Food and Agriculture Organization (UNFAO) estimated that 925 million people around the world were
undernourished. Poverty affects both rural and urban people, especially
in the least developed regions. About 1.3 billion people live on less than
$1.25 per day, so they have few resources to purchase food. In addition,
diverting crops to use as biofuels raises food prices, which increases
malnutrition problems. Subsistence agriculture—farming to grow only
enough food for local use—is challenged by drought, degrading soil quality, high levels of conflict, and changing climate.
The number of people living in extreme poverty has declined by nearly
half a billion since 1980. This achievement is largely the result of rapid
economic development in East Asia, especially in China and India.
However, Figure 1.6 shows that although the world’s grain production has
increased for 50 years, it has not grown as fast as the world’s population.
To feed the people of the world in 2050, we will need to produce more
food. As well, we will need to abolish poverty, among both rural and urban people. Increasing the productivity of the world’s subsistence farmers
would help achieve both goals.
382
Unit 4: Water, Air, and Land
©Les Stone/Sygma/Corbis
More Income and More Food
Figure 1.6
World Grain Production Per Person, 1950–2011
2500
400
Grain per person
350
2000
300
250
1500
Grain production
1000
200
150
100
500
50
0
1950
1960
1970
1980
1990
2000
Grain per person (kg)
Grain production
(in millions of metric tons)
Grain Production Worldwide grain
production has increased steadily over
time, but not as rapidly as the population
has grown.
0
2011
Year
Source: U.S. Department of Agriculture
The Green Revolution
Between 1950 and 1970, Mexico increased its production of wheat eightfold and India doubled its production of rice, without increasing the
area of farmland used. These spectacular increases were called the green
­revolution. They resulted from new varieties of grain. The new varieties
produce large yields if they are supplied with enough water, fertilizer, and
pesticides. The green revolution reduced the price of food and improved
the lives of millions of people.
Figure 1.7
Wheat Varieties This agricultural
research scientist is checking the
growth of wheat in an experimental plot.
©Nigel Cattlin/Photo Researchers, Inc.
The green revolution had limitations, however. Most of the increases
that resulted from the green revolution came from large farms, which
continue to increase their productivity. Because subsistence farmers
often live in extreme poverty, they do not have the money to acquire the
water and chemicals that the new crop varieties need.
In addition, subsistence farmers cannot use much machinery because their farms generally consist of less than two acres. Subsistence
­farmers need small-scale irrigation systems and high-value crops, such
as ­vegetables and fruits, that they can sell. As shown in Figure 1.7, much
research today is devoted to developing plant varieties that produce high
yields of nutritious food on poor soil, using as little water and expensive
chemicals as possible. Distributing the seeds and technology to scattered
rural farms remains a problem to be solved.
Section 1 Formative Assessment
Reviewing Main Ideas
1. Identify the major causes of malnutrition.
2. Compare the environmental costs of
producing different types of food.
3. Explain how malnutrition today is linked to
poverty and violence.
4. Describe the importance and effects of the
green revolution.
Critical Thinking
5. Identify Relationships Study the graph in
Figure 1.6. World grain production increased
during the 1990s. Why did the amount of grain
per person decline during that decade?
6. Infer Relationships Write a short paragraph
that explains how a decrease in the production
of grain worldwide could lead to a shortage of
other food sources.
Chapter 15: Food and Agriculture
383