Download Answers to Mastering Concepts Questions

Mastering Concepts
29.1
1. How do the skeletal and muscular systems interact?
Muscles pull against the skeleton to move the body.
2. Describe similarities and differences among the three main types of skeletons.
The three main types of skeletons are the hydrostatic skeleton, exoskeleton, and
endoskeleton. All three skeletons have attached muscles that pull against them, but they
differ in several ways. The hydrostatic skeleton is flexible and consists of a constrained
fluid. The exoskeleton is external and often must be molted as the animal grows. The
endoskeleton consists of solid internal structures that grow along with the animal.
29.2
1. What are the components of the axial and appendicular skeletons?
The axial skeleton, located in the longitudinal central axis of the body, consists of the
skull, vertebral column, and ribs. The appendicular skeleton consists of the appendages
(upper and lower limbs), and the bones that support them (pectoral girdle and pelvic
girdle).
2. What are the locations of the pectoral and pelvic girdles?
The pectoral girdle, which attaches to the arms, is in upper part of the body. The pelvic
girdle, which attaches to the legs, is in the lower part of the body.
29.3
1. Describe the organization and functions of bone tissue and cartilage.
Bone tissue and cartilage are connective tissues with cells embedded in a solid matrix. In
bone, the matrix is mineralized collagen. The collagen gives bones flexibility, elasticity,
and strength. A cross section of bone reveals concentric rings connected by canals
containing nerves and blood vessels. In cartilage, cells called chondrocytes are
embedded in a matrix of collagen, other protein fibers, and water. The protein fibers give
cartilage resilience, strength, and elasticity, and the water makes it a good shock
absorber. Cartilage has no blood supply, however, so it is slow to heal from injury.
2. What are the differences between spongy bone and compact bone?
Compact bone and spongy bone differ in density. Compact bone is dense and consists of
closely packed cylinders of bone tissue. Spongy bone is hard, but it has many large
spaces in a web of bony struts, which makes it lighter. Red marrow, a nursery for blood
cells and platelets, fills these spaces. Osteocytes in spongy bone acquire nutrients and
oxygen directly from the nearby bone marrow.
3. How are bones remodeled and repaired throughout life?
In an embryo and early fetus, bones consist of cartilage. Before birth, however, boneforming cells enter the cartilaginous matrix and begin to secrete the bony matrix. As the
child grows, the replacement of cartilage by bone occurs at growth plates at the ends of
bones. A person’s bones are fully grown by the early 20s. The bones become thicker and
denser through heavy exercise and, conversely, become lighter and less dense from lack
of exercise. Throughout life, specialized bone cells break down bone tissue if blood
calcium concentrations dip too low. In addition, if a bone is broken, bone cells near the
site repair the break.
4. How do bones participate in calcium homeostasis?
When blood levels of calcium are too low, parathyroid hormone stimulates bones to
release calcium ions into the bloodstream. In contrast, when blood levels of calcium are
too high, calcitonin stimulates bones to absorb calcium ions from the bloodstream and
deposit it in the bone matrix.
5. What are the relationships among joints, tendons, and ligaments?
A joint is a location where two bones meet. A ligament consists of connective tissue that
holds the bones together in a joint. A tendon consists of connective tissue that connects a
muscle to a bone.
29.4
1. What is an antagonistic pair of muscles?
An antagonistic pair of muscles moves a bone in a back-and-forth motion. Contraction of
one muscle pulls the bone in one direction; contraction of the second muscle pulls the
bone in the opposite direction.
2. Describe how sliding filaments shorten a sarcomere.
A sarcomere consists of thick myosin filaments and thin actin filaments that can slide
past one another. As a muscle contracts, the pivoting head of a myosin filament swings
out and connects with actin to form a cross bridge. When the myosin head bends, the thin
filament then slides between the thick filaments, shortening the sarcomere.
3. Explain how electrical impulses trigger muscle contraction.
Electrical impulses that reach the end of a motor neuron’s axon trigger the release of
neurotransmitters. When the neurotransmitters bind to receptors on a muscle cell, they
initiate an electrical impulse in the muscle cell that spreads along the cell membrane and
down T tubules. The electrical impulse cues the release of calcium into sarcomeres,
which allows muscles to contract.
29.5
1. Describe the role of creatine phosphate in muscle metabolism.
A muscle cell’s supply of ATP is quickly exhausted, but creatine phosphate donates a
high-energy phosphate to ADP to quickly regenerate ATP.
2. What happens when a muscle cell cannot generate ATP by aerobic respiration?
Muscle cells switch to fermentation when they cannot generate ATP by aerobic
respiration.
29.6
1. How can one muscle make small and large movements?
The same muscle can generate both small and large movements because it contains motor
units of various sizes. The more motor units are engaged, the larger the movement.
2. How do slow- and fast-twitch muscle fibers differ?
Slow- and fast-twitch muscles differ in their size and endurance. Slow-twitch muscles
(“red meat”) are smaller and have ample supplies of oxygen to support aerobic
respiration, which is required for high-endurance activities. Fast-twitch muscles (“white
meat”) are larger and lack a rich blood supply, so they rely on anaerobic metabolic
pathways to fuel short, powerful contractions with low endurance.
3. How does exercise strengthen muscles?
Exercise causes muscle cells to grow larger; increases the concentration of active
enzymes and the abundance of mitochondria in muscle cells; and increases the blood
supply to muscles.
29.7
1. Summarize the hypothesized relationship between the myosin gene mutation and brain
size in humans and other primates.
The mutation of the myosin gene is only expressed in the muscles that humans use for
chewing; the mutation does not occur in other primates. As a result, human chewing
muscles are smaller and weaker than those of other primates. Researchers hypothesize
that the smaller chewing apparatus allowed for increased brain size in humans.
2. Describe the lines of evidence that support this hypothesis.
The mutation is only present in humans and occurred at the same time as the trend in the
increase in brain size during human evolution.
Write It Out
1. Distinguish among a hydrostatic skeleton, an exoskeleton, and an endoskeleton. What
are the advantages and disadvantages of each type of skeleton? Give an example of an
animal with each.
A hydrostatic skeleton (hydro- means water) consists of fluid constrained within a layer
of flexible tissue. This is the simplest type of skeleton, but because it does not consist of
hard parts, it does not protect the animal’s body. An example of an animal with a
hydrostatic skeleton is a jellyfish. An exoskeleton (exo- means outside) is hard and
protects an animal from the outside, much like a suit of armor. Molting, however, leaves
the animal vulnerable until it produces a new exoskeleton; moreover, exoskeletons are
too heavy for large animals. A beetle has an exoskeleton. An endoskeleton (endo- means
inner) is an internal support structure. Its chief advantage is that it can grow with the
animal, but it does not protect the animal’s surface. Humans have endoskeletons.
2. What role does cartilage play in the vertebrate skeletal system?
Bony skeletons start out as cartilage “models” that are eventually replaced by bone as the
animal develops. Cartilage covers the ends of bones at moveable joints, reducing friction.
Cartilage disks between vertebrae absorb shocks and enhance flexibility. Cartilage
between the ribs and nearby bones allows muscles to elevate the ribs, a movement
important in breathing.
3. Use the Internet to research bone marrow transplants. What do patients who receive
these transplants have in common?
In a bone marrow transplant, healthy bone marrow is used to replace abnormal or
damaged bone marrow that does not produce normal blood cells. The healthy marrow can
come from a patient’s own body (for example, before treatment for cancer) or from a
donor. Bone marrow transplants are risky procedures reserved for patients with diseases
affecting the blood, such as leukemia or multiple myeloma.
4. Bones typically become stronger with exercise. However, some athletes develop stress
fractures from overexercising. Why might light exercise strengthen bones but intense
exercise cause fractures?
Exercise typically puts moderate stress on bones, and damaged bone cells are constantly
degraded and replaced with new cells. Light exercise a few times a week therefore keeps
bones strong. However, rigorous exercise every day might damage more cells than the
bone can replace, slowly weakening the bone. Eventually the weak bone may develop a
small crack called a stress fracture.
5. Design an experiment to test whether changes in the atmosphere (such as an incoming
thunderstorm) cause joint pain. Then, use the Internet to learn whether researchers have
found evidence to support a connection between weather and joint pain.
[Answers will vary; this is one possible answer.] The experiment could have two groups,
one that experiences laboratory conditions that simulate changing weather (the test
group) and another that does not experience changing conditions (the control group). The
test group will be used to determine if changing conditions are correlated with joint pain.
The control group will reveal how often people feel joint pain when no weather changes
are occurring. In medical studies, little evidence supports the relationship between joint
pain and changes in the weather.
6. How do antagonistic muscle pairs move bones? Give an example of such a pair.
A contracting muscle can pull a bone in only one direction; it cannot push the bone the
opposite way. The body can generate back-and-forth movements because many skeletal
muscles occur in antagonistic pairs whose members operate in opposite directions. For
example, when a person contracts the biceps, the arm bends at the elbow joint.
Contraction of the triceps muscle straightens the arm.
7. Describe four muscle proteins and their functions.
Four muscle proteins are actin, myosin, troponin, and tropomyosin. Actin (thin) filaments
slide between myosin (thick) filaments. Myosin heads form cross bridges that pull the
actin. Troponin is a small protein on tropomyosin that changes shape when bound to
calcium. Tropomyosin is a ribbon-like protein that covers actin and keeps myosin from
binding unless calcium is present.
8. Explain how multiple muscle twitches combine to allow you to lift heavy objects.
A single twitch of a muscle unit causes one jerky movement. However, the central
nervous system coordinates muscle twitches into smooth motions. With many motor units
in multiple muscles contracting simultaneously, you can lift a heavy object, run, jump,
and execute many other actions.
9. What is the role of calcium in bones? In muscle contraction?
Calcium hardens the matrix of the bones. In muscle contraction, stimulation by a motor
neuron triggers the release of calcium ions from the muscle cell’s endoplasmic reticulum.
These calcium ions bind to regulatory proteins that normally block muscle contraction.
As a result, the muscle can contract.
10. Write the sequence of events that leads to a muscle contraction, starting with “An
action potential travels along the axon of a motor neuron.”
An action potential travels along the axon of a motor neuron. The action potential reaches
the end of the axon, and neurotransmitters are released into the synapse. The
neurotransmitters bind to receptor proteins on the muscle fiber. Upon receiving the signal
from the motor neuron, electrical waves spread along the T tubules of the muscle cell
membrane, causing the endoplasmic reticulum to release calcium ions. Calcium binds to
the regulatory protein troponin, which changes shape in a way that moves tropomyosin
and allows actin to bind to myosin. After binding, the myosin head bends, causing the
actin filament to slide past the myosin filament. An ATP molecule binds to the myosin
head, causing actin and myosin to separate. The ATP then splits, releasing energy that
returns the myosin head to its original position. If calcium is still present, then a new
cross bridge forms.
11. The following table shows recent men’s world-record times for various running
events. Graph the distance traveled against the average running speed. How does the
production of ATP by muscles over time explain the graph?
Muscle contraction requires ATP. In the short races (100 and 200 m), which last less than
20 seconds, creatine phosphate quickly replenishes ATP. Longer races require a steady
supply of O2 to support aerobic respiration, which generates ATP as long the lungs and
blood can deliver sufficient O2. Once the demand for O2 exceeds the supply, as in a long
race, the muscles will switch to fermentation to generate ATP. Fermentation does not
require O2 but generates ATP less efficiently than aerobic respiration.
Pull It Together
1. How do bones help maintain blood calcium concentrations?
Bones serve as a reservoir for calcium, releasing calcium when the blood concentration is
too low and absorbing calcium when the blood concentration is too high.
2. Add exercise to the concept map in at least three different places.
“Exercise” leads with “strengthens” to “Bones” and to “Skeletal muscles.” “Exercise”
leads with “promotes growth of” to “Muscle fibers”. “Exercise” leads with “requires
coordinated action potentials through” to “Motor neurons.” “Exercise” leads with
“requires contraction of muscles via interactions between” to “Actin” and “Myosin.”
3. How do fast-twitch muscle fibers differ from slow-twitch fibers?
Fast-twitch muscle fibers specialize in short bursts of power. The cells are relatively
large, use ATP quickly, and store less O2 than slow-twitch muscle fibers. Slow-twitch
muscle fibers specialize in high-endurance activities. The cells are relatively small, use
ATP slowly, and have access to abundant O2 for aerobic respiration.