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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.
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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.
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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.
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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
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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.
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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.
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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.
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