Copyright © 2007 Dorling Kindersley
Food chains begin with plants. The sugars they contain provide energy for plant-eating animals, which in turn feed meat-eaters. All plant parts are possible food sources: leaves, stems, roots, fruits, and seeds. Early people gathered wild plants but then, about 10,000 years ago, the first farmers began to cultivate food plants as crops. Insects, birds, and other animals eat plants too. When they feed on farmers’ crops, they are treated as PESTS.
Rice is the staple diet of more than half of the world’s population. It is grown in flooded fields called paddies, because its roots need to be submerged in shallow water. Farmers have even found a way to grow rice on steep mountains, using terraces. Like wheat, maize, and barley, rice is a cereal (edible grass). Cereals are by far the most important crops, but farmers grow many other food plants, including vegetables, fruit, sugar, and tea.
The winged bean is a traditional crop in Southeast Asia. Its seeds, bean pods, leaves, and roots are all edible and they contain high levels of protein. This makes the bean a versatile food that could help to fight famine elsewhere in the world. Plants with useful characteristics are introduced to new regions of the world all the time.
Rice grains are the seeds of the rice plant. A rice plant’s life cycle has two distinct growth phases. The first, the vegetative phase, is when the seed sprouts and the seedling develops. The plant puts out leaves and grows to about 1.2 m (4 ft) tall. The second phase is the reproductive phase. This is when the plant produces spikelets of flowers. Like most grass flowers, these must be wind-pollinated before they can develop into fruits.
Machines such as combine harvesters help farmers to produce more crops from their land. Chemical fertilizers and pesticides also increase crop yields. However, intensive farming methods may remove natural nutrients and pest-killing predators. Some farmers produce crops organically, without using chemicals.
Plants require nitrates, a usable form of nitrogen, in order to build the complex molecules they need to live and grow. To stop nitrates from being permanently removed from the soil, farmers alternate different types of crops. Legumes (peas and beans) have swellings in their roots, called root nodules, that return nitrates to the soil. They can replace the nitrates used up by last season’s crop.
Over thousands of years, people have improved the yield of crops through selective breeding. That means choosing the seeds of the best plants – the ones with the biggest seeds, tastiest leaves, or best resistance to disease – to grow into new plants in the next season. Maize was first cultivated in Central America, and some primitive forms of the plant still grow there. As a result of selective breeding, modern maize is very different to its wild ancestor. It produces much larger cobs, with uniform rows of sweet-tasting corn kernels. All the basic food crops of the world were developed in this way.
An agricultural scientist, Norman Borlaug was central to the 1960s’ “Green Revolution”, a major effort to reduce world hunger. He received the 1970 Nobel Peace Prize for developing high-yield, disease-resistant varieties of wheat. Today his wheat is grown in Asia, Africa, and South America.
Any organism that harms a crop plant is a pest. Many species of insect eat and damage crops. Some, such as aphids, may carry viruses that cause plant disease. Some fungi also cause disease. Weed plants are considered pests too, because they compete for the nutrients in the soil.
Ladybirds are important predators of aphids. Sometimes predators are deliberately introduced to keep aphids or other pests off crops, usually in an enclosed environment such as a greenhouse. Using nature to control pests is called biological pest control. Farmers can also control pests biologically by infecting them with diseases that are harmful only to them.
Chemicals called pesticides are often used to poison pests. They are usually very efficient, allowing farmers to grow fruits and other crops without wastage due to pest damage. However, pesticides can also kill harmless or beneficial organisms, such as honey bees. In apple orchards, honey bees are essential because they pollinate the flowers. Without them, there would be no fruit.