Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
26.1
1. How do the skeletal and muscular systems interact?
Skeletal and muscular systems interact to move the body as muscles pull against the
skeleton.
2. Describe similarities and differences among the three main types of skeletons.
All three skeletons have attached muscles that pull against them. Differences between the
three skeletons are that only the exoskeleton is external, only the hydrostatic skeleton is
flexible, and only the endoskeleton allows an animal to become large.
3. How do vertebrate skeletons reveal common ancestry?
Vertebrate skeletons are composed of the same cell types, and many of the bones are
arranged in similar ways.
26.2
1. What are the two subdivisions of the human skeleton?
The major groups of bones that make up the human skeleton are the axial and
appendicular skeletons.
2. What are the locations of the pectoral and pelvic girdles?
The pectoral girdle is in upper part of the body, and consists of the shoulder and collar
bones that attach to the arms. The pelvic girdle is in the lower part of the body and
consists of the hipbones that attach to the legs.
26.3
1. What are the main parts of a long bone?
A long bone contains red and yellow marrow in a marrow cavity. The outer portion of
the bone is compact bone, and along the edge of the end of the bone is cartilage.
2. Describe the structure and functions of bone tissue and cartilage.
Bone and cartilage are both connective tissues that feature 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 of osteons. Bone
cells are held in osteons, connected by canals, and receiving nerve and blood supply. In
cartilage, a matrix of collagen is filled with protein fibers and water. The fibers give
cartilage resilience, strength, and elasticity, and the water makes it a good shock
absorber. Cartilage has no blood supply.
3. What are the relationships among joints, tendons, and ligaments?
A joint is a location where two bones meet. The ligaments are connective tissue that hold
the bones together in a joint. The tendons are connective tissue that connect the muscle
to the bone.
4. How are bones remodeled and repaired throughout life?
Early in life, bones are formed from a cartilage model. As the child grows, the
replacement of cartilage by bone is restricted to the ends of bones. Bones are fully-grown
when the person is in their early 20s. The bones become thicker and denser through
heavy exercise, and become lighter and less dense from lack of exercise. Throughout life,
osteoclasts break down bone tissue if blood calcium concentrations dip too low. In
addition, if a bone is broken, bone cells repair the break.
5. How do bones participate in calcium homeostasis?
When blood levels of calcium are too low, bones release calcium ions into the
bloodstream in response to stimulation by parathyroid hormone. In contrast, when blood
levels of calcium are too high, bones absorb calcium ions from the bloodstream and
deposit it in the matrix in response to stimulation by calcitonin from the thyroid gland.
26.4
1. What is an antagonistic pair of muscles?
An antagonistic pair of muscles moves a bone around a joint in a back-and-forth motion.
Contraction of one muscle pulls a bone in one direction; contraction of the second muscle
pulls the bone in the opposite direction.
2. Describe the levels of organization of a muscle.
Moving from the largest structure to the smallest, a muscle is an organ consisting of
several tissue types, including muscle tissue. Muscle tissue consists of parallel bundles
of cells called muscle fibers. Each muscle fiber contains hundreds of myofibrils, which
are in turn made of many filaments of the proteins actin and myosin.
3. Describe how sliding filaments shorten a sarcomere.
The pivoting head of the thick filament myosin swings out and connects with the thin
filament actin to form a cross bridge. The thin filament then slides between the thick
filaments, shortening the sarcomere.
4. How do ATP, motor neurons, and calcium ions participate in muscle contraction?
Motor neurons release the neurotransmitters that cause the electrical signal in muscle
cells. The electrical signal then causes Ca2+ to leave the endoplasmic reticulum and bind
to troponin so that tropomyosin can move aside. ATP allows for the release of the cross
bridges so that myosin can unbend and prepare for the next pull. ATP also allows for the
active transport of Ca2+ back into the endoplasmic reticulum so the muscle can relax.
5. How can the same muscle generate both small and large movements?
The same muscle can generate both small and large movements, depending on how many
of its motor units are engaged.
26.5
1. Describe the role of creatine phosphate in muscle metabolism.
Muscle contraction requires ATP. Creatine phosphate is a molecule that donates
phosphate to ADP, replenishing the muscle cell's supply of ATP.
2. What happens when a muscle cell cannot generate ATP by aerobic respiration?
When a muscle cell cannot generate ATP by aerobic respiration, it switches to anaerobic
pathways such as fermentation.
26.6
1. Why do endurance sports require a high proportion of slow-twitch muscle fibers,
whereas power sports require more fast-twitch muscle fibers?
Slow- and fast-twitch muscles differ in their supplies of oxygen. Fast-twitch muscles
(larger white fibers) lack a rich blood supply, so they often use anaerobic metabolic
pathways and cannot sustain prolonged contraction. Slow-twitch muscles (smaller red
fibers) have ample supplies of mitochondria, capillaries, and oxygen. They use aerobic
pathways, and can be utilized for endurance sports.
2. How does exercise strengthen muscles?
Through active exercise, muscle cells grow larger; blood supply to the muscles improves
as capillaries become more numerous. Also, exercise increases the concentration of
active enzymes and the abundance of mitochondria in muscle cells.
26.7
1. Summarize the hypothesized relationship between the myosin gene mutation and brain
size in humans and other primates.
The mutation of the myosin gene on chromosome 7 is only expressed in the muscles used
for chewing, making them smaller and weaker. The mutation, not found in other
primates, arose around 2.4 million years ago and coincides with the evolutionary trend
for increased brain size. Researchers hypothesize that the smaller chewing apparatus
allowed for increased brain size.
2. Describe the lines of evidence that support this hypothesis.
The mutation is only present in the human line. The mutations occurred at the same time
as the trend in the increase in brain size during human evolution.
Answers to Write It Out Questions
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 type.
A hydrostatic skeleton (hydro- means water) consists of fluid constrained within a layer
of flexible tissue. Combined with muscle action, a hydrostatic skeleton can provide
locomotion. An example of an animal with a hydrostatic skeleton is a jellyfish. An
exoskeleton (exo- means outside) protects an organism from the outside, much like a suit
of armor. A beetle has an exoskeleton. An endoskeleton (endo- means inner) is an
internal support structure. Humans have endoskeletons. One advantage of a hydrostatic
skeleton is flexibility; a disadvantage is that it provides no protection and little support.
An advantage of an exoskeleton is that it protects the outside of the animal; one
disadvantage is that an animal must periodically shed its protective exoskeleton as it
grows. An advantage of an endoskeleton is that it grows as the animal grows; a
disadvantage of an endoskeleton is that it does not protect the animal from the outside.
2. Explain the observation that animals with exoskeletons and endoskeletons are better
represented in the fossil record than are animals with hydrostatic skeletons. How might
this difference alter scientific interpretations of the fossil record?
Hard body parts fossilize more easily, and therefore sea animals with hydrostatic
skeletons are underrepresented in the fossil record. This can lead to several incorrect
interpretations of the record: that there were fewer soft bodied animals, that soft bodied
animals were less important in the evolutionary history of life, or that hard bodied
organisms evolved quite suddenly.
3. 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, ribs, and sternum. The appendicular skeleton consists of the
appendages (upper and lower limbs), and the bones that support them (pectoral girdle and
pelvic girdle).
4. What role does cartilage play in the vertebrate skeletal system?
In the vertebral column, the vertebrae are separated by cartilage disks that cushion shocks
and enhance flexibility. The flexibility of the cartilage between the ribs and other bones
allows muscles to elevate the ribs, a movement important in breathing. At synovial joints,
cartilage reduces friction where bone moves against bone.
5. 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 osteons. Spongy bone is hard, but it has many large spaces between a web
of bony struts, which makes it lighter. Red marrow, a nursery for blood cells and
platelets, fills the spaces with spongy bone. Spongy bone tissue contains few osteons;
instead, the cells in spongy bone acquire nutrients and oxygen directly from the nearby
bone marrow.
6. Describe the events of bone development from embryo through adulthood.
The matrix of the cartilage model in the embryo hardens with Ca2+ deposits in the fetus.
This change to bone continues in the ends of the bone in the newborn, and then is limited
to the growth plate through childhood and into the early 20’s. Through adulthood, bone
continually remodels with use or disuse, calcium imbalances, or breaks.
7. How can an imbalance in calcium homeostasis lead to osteoporosis?
When blood calcium levels are low, calcium is not deposited in bone. The lack of
calcium in bone leads to osteoporosis.
8. How do antagonistic muscle pairs move bones? Give an example of such a pair.
Antagonistic muscle pairs are pairs of muscles that move a joint's bones in opposing
directions. When one member of the pair contracts, the other relaxes, and the bones move
in one direction (for example, to bend the elbow). In the opposite situation, the bones
move the other way (for example, to extend the elbow). One example of an antagonistic
muscle pair is the upper arm's biceps and triceps muscles, which work together to bend
and extend the elbow.
9. Describe the arrangement of actin and myosin in a muscle cell.
Actin and myosin are arranged parallel to one another and overlapping within the
sarcomere. When a muscle fiber contracts or relaxes, actin and myosin filaments slide
past one another.
10. How do the effects of exercise (or lack thereof) illustrate homeostasis in bones and
muscles?
Less-used bones lose mass as the minerals slowly dissolve. For example, astronauts lose
bone density if they are in a prolonged weightless environment because their
musculoskeletal systems don’t have to work as hard as they do against Earth’s gravity.
Likewise, a muscle exercised regularly increases in size because each muscle cell
thickens. An unused muscle shrinks.
11. How does the muscular system interact with the nervous system? The skeletal
system? The respiratory system? The circulatory system?
The muscular system requires neurotransmitters from the nervous system to generate its
electrical signal. The muscles of the muscular system attach to bones for movement of
the body. The respiratory system brings in the O2 that muscles need for aerobic
respiration, and the circulatory system delivers it through the capillaries.
12. What roles does fluid play in hydrostatic skeletons, cartilage, and movable joints?
The hydrostatic skeleton consists of fluid constrained within a layer of flexible tissue. In
cartilage, water cleanses the tissue and bathes it with dissolved nutrients from nearby
blood vessels. The high water content of the matrix also makes cartilage an excellent
shock absorber. A synovial joint consists of movable bones joined by a fluid-filled
capsule of fibrous connective tissue. A lubricating fluid inside the capsule, combined
with slippery cartilage on the bone ends, allows bones to move against each other in a
nearly friction-free environment.
13. Search the Internet for disorders of the skeletal or muscular system. Choose one such
illness to research in more detail. Describe how the disorder interferes with bone or
muscle function. What causes the disorder? Is a treatment or cure available?
Possible disorders include, but are not limited to: rheumatoid arthritis, osteoporosis,
carpal tunnel system, fibromyalgia, and Duchenne muscular dystrophy. Using
rheumatoid arthritis as an example answer: In rheumatoid arthritis the immune system
attacks the tissues of the synovial joints causing inflammation and, potentially,
destruction of the cartilage covering the ends of the bones. This causes severe pain and,
sometimes, even deformities in the joints as the joint surfaces no longer move smoothly
and easily. While there is no known cure for rheumatoid arthritis, it can be treated with
pain relievers, steroids or other anti-inflammatories, rest, and joint strengthening
exercises.
14. What is the role of calcium in bones? In muscle contraction?
Calcium hardens the matrix of the bones, which help regulate calcium homeostasis. 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.
15. The following table shows recent men’s world-record times for various running
events. Graph the distance traveled against the average running speed, in meters per
second. How does muscle use of ATP over time explain the graph?
Initially, in the shorter duration races (100 and 200 m) creatine phosphate quickly
replenishes ATP. There is a sharp drop in average speed for the 400 m race as creatine
phosphate is exhausted and the muscles switch to the less efficient lactate fermentation.
The longer races (800 m or more) allow the muscles to use aerobic respiration to generate
ATP. Though the ATP doesn’t come in quick bursts, it is steady and continual, and so
the average speeds no longer vary greatly.
Answers to Pull It Together Questions
1. How do bones help maintain blood calcium concentrations?
Bones serve as a reservoir for calcium. Hormones from the parathyroid gland use
negative feedback to control how much calcium is shuttled between bone and blood.
2. How do actin and myosin interact in the sliding filament model of muscle contraction?
Muscle contraction occurs when thick and thin filaments move past one another. Myosin
cross bridges connect to actin filaments and pull them together with use of ATP.
3. Add neurotransmitters and ATP to this concept map.
"Neurotransmitters" connects with the phrase "are released by" to "Motor neurons".
"ATP" connects with the phrase "is required for the contraction of" to "Muscle fibers".
4. Add fast- and slow-twitch muscle fibers to this concept map. How do these two fiber
types differ?
“Fast- and slow-twitch muscle fibers” connect with the phrase “are two different types
of” to “Muscle fibers”.
Slow-twitch muscle fibers use ATP slowly and regenerate it using aerobic respiration.
Fast-twitch muscle fibers burn ATP quickly; they also have fewer capillaries and store
less oxygen than slow-twitch muscle fibers.