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TEKS Biology Lesson 10A TEKS 10A Describe the interactions that occur among systems that perform the functions of regulation, nutrient absorption, reproduction, and defense from injury or illness in animals. TEKS Lesson 10A: System Interactions in Animals How do systems interact to perform the function of regulation in animals? Animals contain a wide variety of organ systems that act together to help the individual survive. In so doing, they help to maintain a relatively constant internal environment for cells and tissue, a process known as homeostasis. The ways in which an animal maintains homeostasis may not be obvious, but for a living organism, they are literally a matter of life and death. Despite their individual differences, nearly all animals have organ systems that perform important functions such as digestion, movement, respiration, and circulation. Coordination between such systems is essential for the maintenance of homeostasis, and that coordination can take a number of forms. In animals, maintaining homeostasis is the most important function of all body systems. Often homeostasis is maintained by feedback inhibition. Feedback inhibition, or negative feedback, is a system in which the product or result of a process limits the process itself. If your house gets too cold, for example, the thermostat turns on the heat. As heat warms the house, the thermostat turns the heater off. Interacting Systems Complex animals, including mammals, use several linked body systems to respond to events in their environment. The nervous system gathers information using cells called receptors that respond to sound, light, chemicals, and other stimuli. Other nerve cells collect and process that information and determine how to respond. Some invertebrates have only a loose network of nerve cells, with no real center. An example of this can be seen in the illustration on the next page. Other invertebrates and most chordates have large numbers of nerve cells concentrated into a brain. Animals often respond to the information processed in their nervous system by moving around. Muscle tissue generates force by becoming shorter when stimulated by the nervous system. Muscles work together with some kind of skeleton to make up the musculoskeletal system. Skeletons vary widely from phylum to phylum. Some invertebrates, such as earthworms, have skeletons that are flexible and function through the use of fluid pressure. Insects and some other invertebrates have external skeletons. The bones of vertebrates form an internal skeleton. Body Temperature Regulation Another example of how body systems work together is the maintenance of body temperature. In the case of human body temperature, several systems of the body must interact to maintain homeostasis. One of the most important of these is the system that carries information from one part of the body to the others—the nervous system. Sensory nerves carry information about body temperature to the part of the brain called the hypothalamus. The hypothalamus processes this information and decides whether to raise or lower body temperature. The hypothalamus then stimulates the release of chemical signals that affect things such as sweating, shivering, and the rate of cellular metabolism throughout the body. In carrying out these functions, the hypothalamus controls the endocrine system, which sends out chemical signals that move through the body through the circulatory system. 1 TEKS Biology Lesson 10A How do systems interact to perform the function of nutrient absorption in animals? From tiny insects that feed on mammals’ blood to bison that feed on prairie grasses to giant blue whales that feed on plankton, all animals are heterotrophs. Heterotrophs are organisms that obtain nutrients and energy from food. In fact, adaptations for different styles of feeding are a large part of what makes animals so interesting. Obtaining Food Animals obtain nutrients in a wide variety of ways, and several systems of the body may be involved in the process. Both herbivores (plant-eaters) and carnivores (meat-eaters) must move to where their nutrients are found, and this involves careful coordination between the nervous system, muscular system, skeletal system, and sometimes the endocrine system. Changes in the mouthparts and digestive systems of animals reflect many adaptations to the physical and chemical characteristics of different foods. For example, carnivores and leaf-eating herbivores usually have very different mouthparts. These differences are typically related to the different physical characteristics of meat and of plant leaves. Carnivores typically have sharp mouthparts or other structures that can capture food, hold it, and “slice and dice” it into small pieces. Carnivorous mammals, such as wolves, have sharp teeth that grab, tear, and slice food the way knives and scissors would. The jawbones and muscles of carnivores are adapted for upand-down movements that chop meat into smaller pieces. 2 TEKS Biology Lesson 10A Herbivores typically have mouthparts adapted to rasping or grinding. To digest leaf tissues, herbivores usually need to tear plant cell walls and expose their contents. To do this, many herbivorous invertebrates, from mollusks to insects, have mouthparts that grind and pulverize leaf tissues. Herbivorous mammals, such as horses, have (a) front teeth and muscular lips adapted to grabbing and pulling leaves and (b) flattened molars that grind leaves to a pulp. The jawbones and muscles of mammalian herbivores are also adapted for side-to-side grinding movements. Digesting Food Animals have evolved many ways of digesting and absorbing food. The simplest animals, such as sponges, digest food inside specialized cells that pass nutrients to other cells by diffusion. This digestive process is known as intracellular digestion. Most animals that are more complex rely on extracellular digestion. Extracellular digestion is the process in which food is first broken down outside cells in a digestive system and then absorbed by the cells. In most animals, the digestive system is a tube that runs from mouth to anus. Glands such as the pancreas contribute to digestion by producing enzymes that break down food molecules. The tube is usually surrounded by smooth muscle whose contractions help speed the passage of material through it, and it is associated with the circulatory system so that nutrients can be absorbed and sent to the rest of the body. Carnivorous invertebrates and vertebrates typically have short digestive tracts that produce fast-acting, meat-digesting enzymes. These enzymes can digest most cell types found in animal tissues. No animal produces digestive enzymes that can break down the cellulose in plant tissue, however. Some herbivores have very long intestines or specialized pouches in their digestive tracts that harbor microbial symbionts that digest cellulose. Cattle, for example, have a pouchlike extension of their esophagus called a rumen (plural: rumina), in which symbiotic bacteria digest cellulose. Animals with rumina, or ruminants, regurgitate food that has been partially digested in the rumen, chew it again, and then re-swallow it. This process is called “chewing the cud.” Absorbing and Processing Nutrients Nutrients absorbed through the lining of the digestive system pass into the circulatory system, where they are carried to cells throughout the body. For many animals, however, the story doesn’t end there. In many animals, including humans, systems interact to regulate the level of the simple sugar glucose. Glucose is obtained from the foods we eat, and cells use glucose from the blood to serve as a source of energy for their everyday activities. Naturally, right after a meal, as the body absorbs food molecules, the level of glucose in the blood begins to rise. That’s where the pancreas, an organ of the endocrine system, comes in. The pancreas secretes insulin. Insulin is a hormone that prompts glucose to move from the blood into body cells, resulting in a lower glucose level in the blood. As the body uses glucose for energy, the pancreas releases stored glucose to keep the level of the sugar from dropping too low. 3 TEKS Biology Lesson 10A The pancreas’s role in keeping blood glucose levels within a certain range is critical. If there is too little glucose, the cells of the nervous system will slow down to the point that you may lose consciousness and pass out. On the other hand, too much glucose gradually damages cells in the eyes, kidneys, heart, and even the immune system. Abnormally high levels of glucose are associated with a disease called diabetes. In diabetes, changes occur in either the pancreas or body cells that affect the cells’ ability to absorb glucose. Diabetes, one of the fastest-growing health problems in the developed world, is the result of failure of homeostasis with respect to blood glucose levels. How do systems interact to perform the function of reproduction in animals? No system is more important to the long-term survival of a species than its reproductive system. The reproductive system produces offspring that help to ensure species survival over many generations. Most animals reproduce sexually by producing haploid gametes. Sexual reproduction helps create and maintain genetic diversity, which increases a species’ ability to evolve and adapt as the environment changes. Many invertebrates and a few vertebrates can also reproduce asexually. Asexual reproduction usually produces offspring that are genetically identical to the parent. It allows animals to increase their numbers rapidly but does not generate genetic diversity. The Reproductive System The principal job of the reproductive system is to prepare and deliver reproductive cells, or gametes. Gametes carry half the number of chromosomes found in body cells. Typically, male animals produce small gametes, called sperm, which swim. Females produce larger gametes called eggs, which do not swim. When haploid gametes join during fertilization, they produce a zygote that contains the diploid number of chromosomes. Reproductive Timing Many animals depend on other systems of the body, especially the nervous system, to determine the right time to engage in reproductive behavior. Deer in North America, for example, generally mate only in the fall. This enables their young to be born in early summer, when nutritional conditions are best. Their nervous systems sense the changes in light-dark cycles that occur in the fall. This causes changes in behavior that encourage mating to take place. Other animals have reproductive cycles that are related to changes in tides, the phases of the moon, or the seasons of the year. In all such cases, proper interactions between the nervous system and the reproductive system are the key to successful reproduction. The Endocrine System In many animals the endocrine system is closely aligned with the reproductive system. The endocrine system coordinates body functions by means of chemical signals known as hormones. In humans, the pituitary gland, part of the endocrine system, produces hormones that regulate the activities of the ovaries (in females) and testes (in males). At the beginning of puberty, signals from the endocrine system activate ovaries and testes, which then begin to produce the primary male and female sex hormones. These hormones, testosterone in males and the estrogens in females, help produce the secondary sexual characteristics associated with puberty. Proper development of both sperm and egg therefore requires careful coordination between the endocrine and reproductive systems. The Placenta and the Circulatory System In placental mammals, embryonic development takes place inside the body of the female. As the embryo develops, specialized membranes form to protect and nourish the embryo. The embryo is surrounded by the amnion, a sac filled with amniotic fluid that cushions and protects the developing embryo. Another sac, known as the chorion, forms just outside the 4 TEKS Biology Lesson 10A amnion. The chorion makes direct contact with the tissues of the uterus. Near the end of the third week of development, small, fingerlike projections called chorionic villi form on the outer surface of the chorion and extend into the uterine lining. The chorionic villi and uterine lining form the placenta. The placenta is the connection between the mother and embryo that acts as the embryo’s organ of respiration, nourishment, and excretion. Across this thin barrier, oxygen and nutrients diffuse from the mother’s blood to the embryo’s blood; carbon dioxide and metabolic wastes diffuse from the embryo’s blood to the mother’s blood. The blood of the mother and that of the embryo flow past each other, but they do not mix. Through the placenta, a close connection forms between the circulatory systems of mother and child, enabling the reproductive system to complete its task of producing a new life. How do systems interact to perform the function of defense from injury or illness in animals? With pathogens all around us, it might seem amazing that most of us aren’t sick most of the time. Why are we usually free from infections, and why do we usually recover from pathogens that do infect us? One reason is that the systems of our bodies work together to produce a powerful and adaptable series of defenses that protect us against a wide range of pathogens. The Integumentary System The largest single organ in the body is our skin, which makes up a large part of the integumentary system. In many animals, skin may be covered with scales, fur, or even thick, bony plates, forming a first line of defense against injury and attack. But for many animals, the most important protective function of the skin is to keep pathogens, or disease-causing organisms, outside the body. Very few pathogens can penetrate the layers of dead cells that form the skin’s surface. But your skin doesn’t cover your entire body. Pathogens could easily enter your body through your mouth, nose, and eyes—if these tissues weren’t protected by other nonspecific defenses. For example, saliva, mucus, and tears contain an enzyme that breaks down bacterial cell walls. Mucus in the nose and throat traps pathogens, and cilia push the mucous-trapped pathogens away from the lungs. Stomach secretions destroy many pathogens that are swallowed. Inflammatory Response If pathogens do make it into the body—through a cut in the skin, for example—the body’s second line of defense swings into action. These mechanisms include a powerful reaction known as the inflammatory response. The inflammatory response gets its name because it causes infected areas to become red and painful, or inflamed. As shown in the figure below, the response begins when pathogens stimulate cells to release chemicals known as histamines. Histamines increase the flow of blood and fluids to the affected area. Fluid leaking from expanded blood vessels causes the area to swell. White blood cells move from the circulatory system into infected tissues. Many of these white blood cells are phagocytes, which engulf and destroy bacteria. All this activity around a wound may cause a local rise in temperature, which is why a wounded area sometimes feels warm. 5 TEKS Biology Lesson 10A The Immune System The main function of the immune system is to inactivate or kill foreign substances or cells that enter the body. A healthy immune system recognizes all cells and proteins that belong in the body, and it treats these cells and proteins as “self.” It recognizes chemical markers that act like a secret password that says, “I belong here. Don’t attack me!” Because genes program the passwords, no two individuals—except identical twins—ever use the same password. This ability to recognize “self” is essential, because the immune system controls powerful cellular and chemical weapons that could cause problems if turned against a body’s own cells.How does the immune system recognize “foreign” cells and substances? Immune defenses are triggered by molecules called antigens. An antigen is any foreign substance that can stimulate an immune response. Typically, antigens are located on the outer surfaces of bacteria, viruses, or parasites. The immune system responds to antigens by increasing the number of cells that either attack the invaders directly or produce proteins called antibodies. The main role of antibodies is to tag antigens for destruction by immune cells. The immune system guards the entire organism, which means its cells must travel throughout the body, patrolling through the circulatory system as well as other systems of the body. The main working cells of the immune response are B lymphocytes (B cells) and T lymphocytes (T cells). B cells are produced in, and mature in, red bone marrow. T cells are produced in the bone marrow but mature in the thymus—an endocrine gland. Each B cell and T cell is capable of recognizing one specific antigen. When mature, both types of cells travel to lymph nodes and the spleen, where they will encounter antigens. Although both types of cells recognize antigens, they go about it differently. B cells, with their embedded antibodies, discover antigens in body fluids. T cells must be presented with an antigen by infected body cells or by immune cells that have encountered antigens. When either type of lymphocyte encounters an antigen, the lymphocytes organize a powerful immune response that helps to counteract the infection. One of the most interesting properties of the immune system is that it has a kind of “memory” for the infections it has encountered. The specific B and T cells that have been stimulated by a particular antigen grow and divide to form a pool of “memory” cells ready for a second encounter with the same antigen. If pathogens carrying the same antigens appear again, much larger numbers of cells are ready to fight the infection, and the immune response is even more effective. This is why vaccines are so effective in preventing disease. When you are inoculated with a vaccine against polio or measles or diphtheria, a small amount of the antigen found on these pathogens is introduced into your body. The immune system reacts to the vaccine by producing thousands of memory cells. That way, if you are exposed to the real thing, the active pathogen, your immune system is able to fight off the infection quickly and with no ill effects. 6 TEKS Biology Lesson 10A 1. Define Organisms that must obtain nutrients and energy by eating other organs are A multicellular. B autotrophic. C eukaryotic. D heterotrophic. 2. Review The body’s most widespread defense against pathogens is (are) A tears. B mucus. C saliva. D skin. 3. Review All of the following prevent pathogens from entering the human body EXCEPT A red blood cells. B mucus. C tears. D skin. 4. Review Which of the following is NOT part of the inflammatory response? A White blood cells rush to infected tissues. B Blood vessels near the wound shrink. C Phagocytes engulf and destroy pathogens. D The wound becomes red. 5. Describe Describe the interactions that occur among systems that perform the function of regulation in animals. 6. Review How do endocrine glands help regulate body activities? 7. Describe Describe the interactions that occur among systems that perform the function of nutrient absorption in animals. 8. Compare Compare the processes of intracellular and extracellular digestion. 9. Describe Describe the interactions that occur among systems that perform the function of reproduction in animals. Use humans as your example. 10. Compare Compare sexual reproduction and asexual reproduction in terms of the genetic diversity resulting from each. 11. Describe Describe the interactions that occur among systems that perform the function of defense from injury or illness in animals. 12. Infer Which body systems are most involved when a raccoon discovers that a full trashcan is a good source and it knocks over the can to find the food? Explain. 7