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figure 32-1

Capturing fast-moving prey requires exquisitely timed coordination between the nervous tissue and muscle tissue in the body of this heart-nosed bat, Cardioderma cor.

Capturing fast-moving prey requires exquisitely timed coordination between the nervous tissue and muscle tissue in the body of this heart-nosed bat, Cardioderma cor.

Heterotrophy

Plants and some unicellular organisms are autotrophic. They make food using simple molecules from their environment and an energy source, such as the sun. Animals, on the other hand, are hetero-trophic. They must obtain complex organic molecules from other sources. Most animals accomplish this by ingestion. During ingestion, an animal takes in organic material or food, usually in the form of other living things. Digestion then occurs within the animal's body, and carbohydrates, lipids, amino acids, and other organic molecules are extracted from the material or cells the animal has ingested.

Sexual Reproduction and Development

Most animals can reproduce sexually, and some can also reproduce asexually. In sexual reproduction, two haploid gametes fuse. The zygote, the diploid cell that results from the fusion of the gametes, then undergoes repeated mitotic divisions. Mitotic division of a cell produces two identical offspring cells. How does an adult animal, with its many different organs, tissues, and cell types, arise from a single cell? In the process called development, the enlarging mass of dividing cells undergoes differentiation. During differentiation (DlF-uhr-EN-shee-AY-shuhn), cells become specialized and therefore different from each other. For example, some cells may become blood cells, and others may become bone cells. The process of differentiation is the path to cell specialization.

Movement

Although some animals, such as barnacles, spend most of their lives attached to a surface, most animals move about in their environment. The ability to move results from the interrelationship of two types of tissue found only in animals: nervous tissue and muscle tissue. Nervous tissue allows an animal to detect stimuli in its environment and within its own body. Cells of nervous tissue, called neurons, conduct electrical signals throughout an animal's body. Multiple neurons work together to take in information, transmit and process it, and initiate an appropriate response. Often, this response involves muscle tissue, which can contract and exert a force to move specific parts of the animal's body. The bat shown in Figure 32-1 continuously processes information about its position in space and the position of its prey. It can adjust its muscular responses so rapidly that it can intercept insects in flight.

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