How Do We Know When We Are Hungry?
How Do We Know When We Are Hungry? Hunger begins when substances like glucose (sugar), minerals, vitamins, and amino acids are missing from the blood. Nerves in the...
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What Is Soil?
Soil is a mixture of very small pieces of rock and rotted materials from plants and animals. This rotting plant and animal material, called humus, gives soil its dark...
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How Is Petrified Wood Formed?
How Is Petrified Wood Formed? Wood that is petrified has been changed by nature into stone. Petrified wood is a fossil. It forms when plant material is buried by...
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Why Do Plants Have Sap?
Why Do Plants Have Sap? Sap is the liquid that enables trees and other plants to live and grow. The roots of a plant draw water, along with dissolved minerals, from the...
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Where Does Sand Come from?
Sand is made from tiny grains of rocks and minerals. Almost every grain of sand was once part of a big rock. Heat and cold caused cracks in the rocks, and wind and...
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