Download Answers to Mastering Concepts Questions

Answers to Mastering Concepts Questions
Chapter 31
31.1
1. Skeletal and muscular systems interact to move the body as muscles pull against the
resistance of the skeleton.
2. A hydrostatic skeleton consists of a constrained fluid; contraction of muscles in the tissue
surrounding the fluid provides locomotion.
3. Exoskeletons are on the body’s exterior and may be shed periodically as an animal grows;
endoskeletons are within the body and grow along with the animal. In addition, whereas
exoskeletons often made rigid by deposits of calcium, endoskeletons are composed mostly of
bone.
4. Vertebrate skeletons are composed of the same cell types, and many of the bones are
arranged in similar ways.
31.2
1. The major groups of bones that make up the human skeleton are the axial and appendicular
skeletons.
2. The pectoral girdle is in upper part of the body and consists of the shoulder and collar bones
that attach to the arms. The pectoral girdle is in the lower part of the body and consists of the
hipbones that attach to the legs.
31.3
1. 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 in which bone cells are held
in pockets connected by canals and receiving nerve and blood supply. In cartilage, a matrix of
collagen is filled with protein fibers and chondrocytes that secrete cartilage. The fibers give
cartilage resilience, strength, and elasticity. A cross section of cartilage shows fibers and a
scattering of cells that secrete cartilage and elastin fibers. Cartilage has no blood supply.
2. Osteoclasts destroy bone tissue, ostoeblasts build bone tissue, and osteocytes are former
osteoblasts that are located within osteons.
3. Osteons are microscopic structures that look like concentric rings within bony tissue. In an
osteon, a space that contains a bone cell is connected to other such spaces by canals. Blood
vessels and nerves are the center of the osteon. Osteons are most abundant in compact bone.
4. Early in life, after cartilaginous bones have been formed, osteoblasts enter the cartilaginous
matrix and secrete the bony matrix around themselves. As the child grows, the replacement of
bone by cartilage is restricted to the ends of bones. Bones are fully grown when the person is
about 20 years old. 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, osteoblasts repair the
break.
5. 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 in response to stimulation by calcitonin
from the thyroid gland.
6. The structures in a synovial joint include two adjacent bones that are connected by ligaments.
The surfaces of these bones are covered with cartilage, and a capsule of fibrous connective
tissue surrounds the pair of bones. The inner membrane of the capsule secretes a fluid that
lubricates the joint, making it freely movable.
31.4
1. An antagonistic pair of muscles moves the same joint. Contraction of one muscle extends the
joint; contraction of its antagonist flexes it.
2. 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 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. Interactions between actin and myosin move muscles by forming crossbridges that allow the
filaments to move relative to one another. When many actin and myosin filaments simultaneously
move relative to one another, a muscle contracts.
4. ATP is the source of energy that powers muscle contraction.
5. Motor neurons control skeletal muscle contraction by releasing a neurotransmitter,
acetylcholine, at the synapse between the motor neuron and a muscle cell. The resulting
depolarization stimulates the release of calcium ions from the endoplasmic reticulum. Calcium
ions interact with proteins that prevent actin from forming crossbridges with myosin. When
crossbridges can form, the muscle can contract.
6. In muscle contraction, creatine phosphate serves as a source of phosphate groups to
regenerate ATP from ADP.
7. When O2 is not readily available, a muscle will switch from aerobic respiration to fermentation
to generate ATP. This would happen when muscles are working hard, such as when a person is
exercising and runs out of breath.
31.5
1. The same muscle can generate both small and large movements, depending on how many of
its motor units are engaged.
2. Slow- and fast-twitch muscles differ in their supplies of oxygen from myoglobin molecules.
Fast-twitch muscles (white fibers) lack myoglobin and don’t have a rich blood supply, so they
often use anaerobic metabolic pathways and cannot sustain prolonged contraction. Red muscles
are slow-twitch muscles that have ample supplies of myoglobin and ample blood supplies. They
use aerobic pathways.
3. As a result of regular exercise, muscles grow as individual cells increase in size.