The document discusses the relationship between biological structure and function. It explains that structures adapted for specific functions, like incisors that cut food and molars that mash it. The human body is organized into hierarchical levels from cells to tissues to organs to organ systems. For example, heart muscle cells form heart muscle tissue, which makes up the heart organ that is part of the circulatory system. Different organ systems work together for the organism to survive, like respiratory and digestive systems providing oxygen and nutrients so the circulatory system can function.

1. Biology Concept 27.1 StructureFitsFunctions in theHumanBody

2. Key Terms anatomy: study of an organism's structure physiology: study of functions or processes in an organism tissue: cooperating unit of many similar cells that perform a specific function organ: unit consisting of several tissues that together perform a specific task organ system: unit of multiple organs that together perform a vital body function

3. Anatomy and Physiology A close look at a biological structure often provides clues about its function. Structures that look alike often have similar functions. For example, if you look at your teeth in a mirror, you'll see thin-edged, sharp teeth in front called incisors (Figure 27-1). Their shape may remind you of the sharp blade of a cutting tool, such as a knife. Indeed, the function of incisors is to cut through pieces of food.

4. Figure 27-1Incisors and molars have different structures that fit their different functions. Molars have a bumpy surface that mashes food. Incisors have a sharp, thin edge that cuts food.

5. Anatomy and Physiology The teeth in the back of your mouth, molars, have many sharp bumps that resemble a meat tenderizer's hard, bumpy surface. Just as a chef pounds a tenderizer against a tough piece of meat to soften it before cooking, molars grind and mash food before it is swallowed.

6. Anatomy and Physiology The study of the structure of an organism and its parts is called anatomy. For example, the anatomy of your mouth reveals how many teeth you have, their shapes, and their position in your jaw. Physiology (fizee AWL uh jee) is the study of what structures do, and how they do it—in other words, their function. Studying how your jaw moves your teeth when you chew and how your teeth cut and mash your food is physiology.

7. Levels of BodyStructure As in other multicellular organisms, your body has several levels of organization. Figure 27-2 shows the structures that make up one system in your body, the circulatory system. The first level is the cell, such as a muscle cell in your heart. Each heart muscle cell is branched, allowing it to interlock with other surrounding heart muscle cells, much as jigsaw puzzle pieces fit together. This interlocking helps coordinate the actions of neighboring cells. Together, these cells form a muscle tissue.

8. Levels of BodyStructure A tissue is a cooperating unit of many similar cells that perform a specific function. In this case, the tight organization of the muscle cells allows the muscle tissue to produce heartbeats that pump blood. In addition to muscle tissue, the other major types of tissue are epithelial, connective, and nervous tissue.

9. Figure 27-2The smallest level of organization shown in this diagram is the cell. Cells working together make up a tissue, which in turn is part of an organ. Organs working together form the different organ systems that make up a whole organism.

10. Levels of BodyStructure An organ consists of several tissues that together perform a specific task. For example, your heart is an organ composed of muscle and other tissues, such as nervous tissue, that together produce a pumping action. An organ system consists of multiple organs that together perform a vital body function. The organs of the circulatory system are the heart and blood vessels. Together, they constantly transport blood throughout the body.

11. Levels of BodyStructure The highest level of structure is the whole organism, in this case a human being. Different organ systems work together, contributing to the successful function of the whole organism. For example, without oxygen supplied by the respiratory system and nutrients provided by the digestive system, the heart cannot pump blood and the circulatory system cannot function.

12. Levels of BodyStructure Another example is the coordination of the nervous, muscular, and skeletal systems in moving parts of the body. Nerves stimulate muscles to contract, and the muscles in turn move the bones of the skeleton to which they are attached. Figure 27-3 introduces the major functions and organs of 12 organ systems in the human body.

13. Figure 27-3aThis diagram shows 12 organ systems in the human body. Note the major organs that make up each system..

14. Figure 27-3bThis diagram shows 12 organ systems in the human body. Note the major organs that make up each system..