* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Maintaining a Dynamic Equilibrium The Need for Homeostasis
Survey
Document related concepts
Cell culture wikipedia , lookup
Natural environment wikipedia , lookup
Neuronal lineage marker wikipedia , lookup
Chimera (genetics) wikipedia , lookup
Induced pluripotent stem cell wikipedia , lookup
Precambrian body plans wikipedia , lookup
Hematopoietic stem cell wikipedia , lookup
Human embryogenesis wikipedia , lookup
Cell theory wikipedia , lookup
Dictyostelium discoideum wikipedia , lookup
Regeneration in humans wikipedia , lookup
Adoptive cell transfer wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Microbial cooperation wikipedia , lookup
State switching wikipedia , lookup
Transcript
THEME III Maintaining a Dynamic Equilibrium 10 The Need for Homeostasis HOMEOSTASIS Hair Surface of skin Organisms live in a world of changing conditions. But, to remain alive, every organism needs to keep the conditions inside of itself fairly constant. An organism must have ways to keep its internal conditions from changing as its external environment changes. This ability of all living things to detect deviations and to maintain a constant internal environment is known as homeostasis. An obvious change that has occurred in the course of evolution is the development of larger multicellular organisms from microscopic, single-celled ones. Is there an advantage to being multicellular? Being microscopic and single-celled makes it difficult for an organism to maintain homeostasis. Having a multicellular body makes possible many types of protection against changes in the environment. In other words, an organism with many cells is able to have structures and systems that protect its individual cells from external changes, thus helping it to stay alive. (See Figure 10-1.) To maintain homeostasis, organisms actually must make constant changes. That is why 72 Blood vessels Figure 10-1 Multicellular organisms have systems and structures that help them maintain homeostasis. For example, our skin has features that detect and respond to changes in external temperature. homeostasis is often referred to as maintaining a dynamic equilibrium. Dynamic means “active,” and equilibrium means “balanced.” Homeostasis requires active balancing. THE CELL AND ITS ENVIRONMENT One of the most fascinating facts about our bodies is that each of our many, many cells is Chapter 10: The Need for Homeostasis Capillary Lymph Red blood cells 73 Skull Cerebrum Lymph vessel ICF Tissue cells Figure 10-2 All the cells in our body are surrounded by intercellular fluid (ICF). Materials are exchanged between the cells and the fluid, which helps to maintain stable conditions inside each of the cells. Medulla Cerebellum Spinal cord surrounded by liquid. The smallest blood vessels in our bodies, the capillaries, are close to every cell. There is a small amount of space between the capillaries and the body cells. This space is filled with fluid. The fluid that surrounds cells is made up mostly of water, with many substances dissolved in it. This intercellular fluid is important in helping to maintain stable conditions inside each of our cells. Many materials are exchanged between the cells and the fluid. In turn, materials may be exchanged between the fluid and the blood in the capillaries. All of this is done to make sure that each and every body cell is able to maintain homeostasis and remain healthy. (See Figure 10-2.) Vertebrae Figure 10-3 A structure in the brain (the medulla) monitors the amount of CO2 in the body, adjusting the breathing rate to maintain proper levels. sends signals to the chest to increase the rate of breathing and the amount of air taken in on each breath. These changes in breathing increase the exchange of gases in the lungs, lowering the CO2 levels in the body. These lower levels are then detected in the brain, which in turn sends a signal to reduce the breathing rate. This process is an example of a feedback mechanism. Feedback mechanisms are important in maintaining homeostasis. (See Figure 10-3.) MAINTAINING HOMEOSTASIS WHEN WE EXERCISE FEEDBACK MECHANISMS Exercise involves increased muscle activity. This activity creates changes within the body. To maintain homeostasis, the body needs to be able to respond to these changes. An example of a change that occurs when we exercise is the increase in the body of carbon dioxide (CO2), produced by muscle cells as a result of cellular respiration. The level of CO2 increases in both the intercellular fluid and the blood. To maintain homeostasis, the body first must be able to detect this change and then respond to the change. A structure in the brain detects the increased CO2 level in the blood passing through the brain and in the fluid around the brain cells. As a result, this part of the brain Carbon dioxide levels in your body are regulated somewhat as a thermostat regulates the temperature of your house. A thermostat measures the temperature of the air in a room. When the air temperature in the house falls below a preset figure, the thermostat turns a furnace on. The furnace produces heat, and the temperature of the air in the house increases. When the temperature of the air rises above the preset temperature, the thermostat tells the furnace to shut down. The temperature in the house stops rising, the air begins to cool, and the thermostat continues the cycle of telling the furnace to produce heat or to shut down. (See Figure 10-4.) 74 Reviewing the Living Environment: Biology Thermostat Sensor Stomate Temperature sensors in brain Body temperature control Skeletal muscles Hypothalamus Temperature sensors in skin Sweat glands Chloroplasts Guard cells Nucleus Leaf cells Stomate closed Nucleus Stomate open Figure 10-5 Special openings in the surface of a leaf function to maintain water balance in plants. Superficial arteries Home heating system Figure 10-4 Both CO2 levels and body temperature are regulated by feedback mechanisms, much as a thermostat controls the temperature in a room. In this type of feedback mechanism, a change occurs that produces another change, which in turn reverses the first change. This is an important process in maintaining homeostasis. The following are parts of a feedback mechanism used in maintaining homeostasis: ♦ Sensor. Something must be able to detect a change. A thermometer attached to a thermostat is a sensor. In the body, structures in the brain detect changes in CO2 levels. ♦ Control unit. Something must know what the correct level should be. A thermostat in a house is set to a particular comfort level. Information in the brain is preset at the correct CO2 level. ♦ Effector. Something must take instructions from the control unit and make the necessary changes. In a house, the effector would be a furnace or an air conditioner. In the body, the effector for CO2 levels would be the muscles in the chest that are used for breathing. MAINTAINING HOMEOSTASIS: WATER BALANCE IN PLANTS Maintaining water balance is a major concern for all living things. Plants as well as animals must maintain water balance. Openings in the surface of a leaf are adapted to control the loss of water. Each opening is surrounded by two guard cells. These guard cells, like any cells, allow water to diffuse through their cell membrane. When water is abundant, it moves into the guard cells. The increased quantity of water increases the pressure within the cells. Guard cells are somewhat curved in shape; when they are filled with water, they become even more curved. The space between them expands, the opening widens, and excess water is allowed to evaporate out of the air spaces inside the leaf to the air that surrounds the plant. (See Figure 10-5.) When water becomes scarce, the guard cells become less curved in shape and the opening closes. Water loss is reduced and the plant is able to maintain its water balance. SYSTEMS FOR MAINTAINING HOMEOSTASIS Multicellular animals have evolved highly organized, complex organ systems especially suited to maintaining a relatively constant internal environment. These organ systems include the excretory system, which regulates the chemistry of the body’s fluids while removing harmful wastes; the nervous system, which uses electrochemical impulses to regulate body functions; the endocrine system, which produces hormones—chemical messengers essential in regulating the functions and behavior of the body; and, finally, the immune system, which uses a set of defenses to protect the body from dangerous substances and microorganisms that could upset the internal balance on which life itself depends. Chapter 10: The Need for Homeostasis 75 Chapter 10 Review Part A—Multiple Choice 1. Organisms undergo constant chemical changes as they maintain an internal balance known as 1 2 3 4 interdependence synthesis homeostasis recombination 2. What characteristic has evolved that helps to maintain homeostasis? 1 2 3 4 taller bodies with larger cells shorter bodies with fewer cells multicellular bodies with many cells multicellular bodies with fewer cells 3. A system in dynamic equilibrium 1 2 3 4 makes constant changes changes in intervals or steps changes very infrequently never changes at all 4. Intercellular fluid is made up mostly of 1 2 3 4 water blood mineral salts cytoplasm 5. Intercellular fluid is important for the exchange of materials between 1 2 3 4 body cells and arteries body cells and veins veins and capillaries body cells and capillaries 6. As a result of exercise, CO2 levels increase in the 1 2 3 4 blood only intercellular fluid only blood and intercellular fluid muscles only 7. The brain sends a signal to increase the breathing rate when the CO2 level has 1 2 3 4 not changed for a while decreased increased increased, then decreased 8. The increased breathing rate signaled by the brain serves 1 2 3 4 to increase the CO2 level in the body to decrease the CO2 level in the body to decrease the O2 level in the body no function in changing O2 and CO2 levels 9. In adjusting the CO2 level, the part of the body that acts like a thermostat in the home is the 1 2 3 4 brain chest lungs muscle tissue 10. If an organism fails to maintain homeostasis, the result may be 1 2 3 4 disease only death only disease or death none of the above 11. A change in the body results in another change. This second change reverses the first change in order to maintain homeostasis. This describes a type of 1 2 3 4 control mechanism feedback controller feedback mechanism effector mechanism 12. The effector for adjusting the CO2 level in the body would be the 1 2 3 4 blood tissue brain lungs chest muscles 13. Why might a blood clot be important to maintaining homeostasis? 1 2 3 4 It slows the flow of blood through the body. It prevents the loss of blood from the body. It increases the amount of water in the blood. It adds more cells to the blood tissue. 14. The changing shape of a plant’s guard cells helps to 1 2 3 4 allow the plant to grow stronger prevent the plant from losing food regulate the temperature of the plant maintain the plant’s water balance