Deck 33: Muscle and Movement

Question 1

Which process occurs during shortening of a skeletal muscle?

A) Increase in the distance between Z lines
B) Lengthening of the sarcomere
C) Reduction of the H zone
D) Reduction of the A band
E) Decrease in the area of actin and myosin overlap

Answer 1

C

Question 2

The striated appearance of skeletal muscle is due to the

A) dark color of myosin.
B) multiple nuclei per fiber.
C) regular arrangement of filaments.
D) dense array of microtubules.
E) dense packing of ATP molecules.

Answer 2

C

Question 3

A mutation in the gene encoding troponin has occurred in a mouse.What is a possible effect that this mutation could have on muscle activity?

A) Signals from nerve impulses may be blocked from initiating an action potential in the muscle cell membrane.
B) An action potential may be prevented from traveling down the T tubules.
C) Calcium pumps in the sarcoplasmic reticulum may be blocked from releasing calcium into the sarcoplasm.
D) Increases in calcium concentration in the sarcoplasm may not lead to cross-bridge formation between actin and myosin.
E) Both c and d

Answer 3

D

Question 4

Which remains constant as a skeletal muscle relaxes following contraction?

A) A band
B) H zone
C) I band
D) Distance between Z lines
E) Overall width of a sarcomere

Question 5

A sarcomere is best described as a

A) moveable structural unit within a myofibril bounded by H zones.
B) fixed structural unit within a myofibril bounded by Z lines.
C) fixed structural unit within a myofibril bounded by A bands.
D) moveable structural unit within a myofibril bounded by Z lines.
E) collection of myofibrils.

Question 6

Refer to the diagram of a sarcomere below.Which statement based on the diagram is true?

A) The structure 1 consists of two chains made of monomers.
B) The structure 1 shortens in length as contraction occurs.
C) The structure 2 has a head that hydrolyzes ATP.
D) The zone labeled 3 shortens in length as contraction occurs.
E) The unit labeled 4 maintains a constant length as contraction occurs.

Question 7

How does tropomyosin control muscle contraction?

A) It provides a bridge between actin and myosin.
B) It provides a site where ATP can be utilized.
C) Changes in its position expose myosin-binding sites on actin filaments.
D) It transmits electric charge to the filaments.
E) Changes in its shape cause membrane channels to open.

Question 8

An individual sarcomere unit consists primarily of

A) a stack of actin fibers.
B) a stack of myosin units.
C) overlapping actin and membrane.
D) overlapping myosin and membrane.
E) overlapping actin and myosin filaments.

Question 9

Which statement about myosin is true?

A) A thick filament consists of actin and myosin.
B) Myosin filaments consist of linear troponin molecules attached to tropomyosin heads.
C) Troponin binds to the head of the myosin molecule.
D) Myosin activity is regulated by tropomyosin,which binds to myosin tails.
E) Myosin heads have ATPase activity and interact with actin.

Question 10

The role of Ca²⁺ in the control of muscle contraction is to

A) cause depolarization of the T tubule system.
B) initiate changes in protein conformation that expose myosin-binding sites on actin.
C) change the conformation of myosin heads,thus causing microfilaments to slide past each other.
D) bind to tropomyosin and break actin-myosin cross-bridges.
E) block the ATP-binding site on myosin heads,enabling muscles to relax.

Question 11

When troponin binds calcium,

A) it changes conformation,twisting tropomyosin and exposing the actin-myosin binding site.
B) ion channels open and sodium rushes into the muscle cells.
C) it allows tropomyosin to bind actin.
D) it changes conformation,exposing the ATP binding site and allowing the actin-myosin bond to break.
E) ATP binds to the myosin head,allowing myosin to attach to actin.

Question 12

Refer to the diagram below.Based on the diagram,which sequence represents the stages of muscle contraction in the correct order?

A) A,B,C,D,E,F
B) A,F,E,D,C,B
C) A,C,D,E,F,B
D) A,C,B,F,E,D
E) A,D,C,B,F,E

Question 13

Refer to the figure below.Which statement accurately describes the H zone and I bands of a sarcomere?

A) The H zone and I bands are regions of the sarcomere that appear light under the microscope because they both represent areas where myosin but not actin filaments are present.
B) The H zone and I bands are the only regions of the sarcomere that do not shorten or lengthen as the sarcomere contracts.
C) A shortening of the H zone is always accompanied by a shortening of the I bands,and a lengthening of the H zone is always accompanied by a lengthening of the I bands.
D) Stimulation by an action potential results in a lengthening of the H zone but a shortening of the I bands.
E) The H zone,but not the I bands,change in width during contraction of the sarcomere.

Question 14

Which statement about actin is true?

A) Two strands of tropomyosin are twisted around polymerized actin.
B) Actin carries out the power stroke motion that allows filaments to slide during contraction.
C) Actin is the only protein making up thin filaments in a muscle fiber.
D) Troponin forms the head of the actin molecule.
E) Tropomyosin has ATPase activity and interacts with the actin.

Question 15

What is the role of the sarcoplasmic reticulum in muscle contraction?

A) It stores Ca²⁺ ions for release during contraction.
B) It surrounds and protects the muscle filaments.
C) It provides sites of ATP synthesis.
D) It depolarizes when stimulated by an impulse.
E) It synthesizes actin and myosin filaments.

Question 16

When animals die,muscles stiffen in rigor mortis because

A) muscles cannot contract without ATP.
B) actin and myosin cannot bind without ATP.
C) ATP is required for synthesis of protein filaments.
D) ATP forms cross-bridges between filaments.
E) actin and myosin cannot separate without ATP.

Question 17

What allows muscle fibers to shorten during contraction?

A) Individual protein filaments contract.
B) Cross-bridges between filaments break.
C) Arrays of filaments slide against each other.
D) Protein filaments coil more tightly.
E) Subunits of protein polymers detach.

Question 18

Starting with the arrival of an action potential at the neuromuscular junction,which is the correct order of events?

A) Calcium is released from the sarcoplasmic reticulum,an action potential travels down the T tubule,depolarization spreads through the T tubule,and myosin binds actin.
B) An action potential travels down the T tubule,depolarization spreads through the T tubule,calcium is released from the sarcoplasmic reticulum,and myosin binds actin.
C) An action potential travels down the T tubule,depolarization spreads through the T tubule,calcium is taken up by the sarcoplasmic reticulum,and myosin binds actin.
D) An action potential travels down the T tubule,depolarization spreads through the T tubule,ATP binds to myosin,and myosin binds actin.
E) The T tubule is depolarized,calcium is released from the sarcoplasmic reticulum,an action potential is created in the muscle cell,and myosin binds actin.

Question 19

Refer to the diagram below.Which statement based on the diagram is true?

A) Structure 1 has ATPase activity.
B) Structure 2 blocks sites where myosin can bind.
C) Structure 3 has one subunit that binds myosin.
D) Structure 4 shortens in length as the sarcomere contracts.
E) Structure 5 binds calcium.

Question 20

Which statement about the structure of skeletal muscle is true?

A) The light bands of the sarcomere are the regions where actin and myosin filaments overlap.
B) When a muscle contracts,the A bands of the sarcomere lengthen.
C) The actin filaments are anchored by titin molecules to the Z lines.
D) When a muscle contracts,the H zone of the sarcomere shortens.
E) The sarcoplasm of the muscle cell is contained within the sarcoplasmic reticulum.

Question 21

A chemical compound has been used as a rodent poison for many years although scientists do not know specifically how it causes death.Recently the compound was shown to bind to the dihydropyridine (DHP)receptor.What would be the best question to ask next in continued research about the mechanism of this compound?

A) Does the compound interfere with depolarization of T tubules?
B) Does the compound interfere with the binding of calcium to troponin?
C) Does the compound inhibit an action potential from developing in the muscle cell membrane and traveling down the T tubules in response to a nerve impulse?
D) Does the compound prevent calcium release from the sarcoplasmic reticulum into the sarcoplasm following a nerve impulse?
E) Does the compound prevent cross-bridge release between actin and myosin to allow a new cycle of contraction?

Question 22

An apodeme is

A) an external extension of an exoskeleton.
B) an internal extension of an exoskeleton.
C) a ligament.
D) a tendon.
E) a structural element of hydroskeletons.

Question 23

Calcium ions must bind to which protein to initiate muscle contraction?

A) Myosin
B) Actin
C) Tropomyosin
D) Troponin
E) Titin

Question 24

The role of tendons is to join

A) two bones.
B) two ligaments.
C) bone and ligament.
D) muscle and ligament.
E) muscle and bone.

Question 25

What allows an earthworm to move through soil?

A) Antagonistic pairs of muscles that pull in opposition to one another using elements of an endoskeleton
B) Alternating contractions of circular and longitudinal muscles that push against elements of an endoskeleton
C) Contracting muscles attached to apodemes of an exoskeleton
D) Contractions of muscles that increase pressure on body fluids to extend the body forward
E) Shifting of body fluids from one compartment to another

Question 26

Student 1 states that butterflies have exoskeletons,while student 2 states that before metamorphosis,butterflies exist in caterpillar form and have no skeleton.Which student is correct?

A) Both students are correct.
B) Neither student is correct because butterflies have no skeletons and caterpillars have hydrostatic skeletons.
C) Student 1 is correct;student 2 is incorrect because caterpillars have endoskeletons.
D) Student 2 is correct;student 1 is incorrect because butterflies have no skeletons.
E) Student 1 is correct;student 2 is incorrect because caterpillars have hydrostatic skeletons.

Question 27

Which statement about the endoskeletons of vertebrates is false?

A) The muscles are attached to a living support structure.
B) Endoskeletons are inert systems.
C) Molting is unnecessary in animals with endoskeletons.
D) Endoskeletons consist of bone and cartilage.
E) At least two skeletal structures are required to form a joint.

Question 28

The animals listed in the table below were grouped together because they share certain characteristics.What would be the appropriate heading for this grouping?

A) Marine Animals
B) Vertebrates
C) Animals with Hydrostatic Skeletons
D) Animals with Exoskeletons
E) Animals Lacking Skeletons

Question 29

Using mice,a biologist studying the cycle of protein interactions in muscle contraction has induced a mutation in one of the genes encoding proteins involved in this cycle.She finds that the muscle fibers expressing this mutation are not able to contract.Upon further investigation,she finds that calcium release into the sarcoplasm is normal,and calcium binding to protein filaments is normal.Which hypothesis could explain this mutation?

A) The mutation occurs at the site on actin where myosin binds.
B) The mutation occurs in a region of tropomyosin that undergoes conformational change to expose the myosin-binding site on actin.
C) The mutation occurs in the myosin tail region,preventing titin binding to myosin.
D) The mutation occurs in myosin and prevents release of inorganic phosphate from the ATP binding site.
E) All of the above

Question 30

How are endoskeletons similar to exoskeletons?

A) Both consist of the same biomaterials.
B) Both use antagonistic pairs of muscles to cause motion.
C) Both cover and surround all of the soft tissues of an organism.
D) Both represent inert,nonliving tissue.
E) Both use muscles pushing against body fluids to cause motion.

Question 31

How are endoskeletal systems similar to hydrostatic skeletal systems?

A) Both skeletal systems allow for complex movements.
B) Organisms with these skeletal systems have optimal protection from predators.
C) Organisms with these skeletal systems do not have to undergo molting.
D) Both skeletal systems support very large-size organisms.
E) Both skeletal systems are represented widely in terrestrial animals.

Question 32

A role of cartilage in the adult human skeleton is to

A) bear heavy loads.
B) add flexibility.
C) be lightweight.
D) sustain vibrations.
E) grow rapidly.

Question 33

Which two animals have the same type of skeletal system?

A) Whale and earthworm
B) Squid and crab
C) Trout and moth
D) Ant and lobster
E) Hawk and dragonfly

Question 34

A grasshopper is capable of jumping extremely long distances.What is the most likely explanation of the mechanism that makes this possible?

A) The grasshopper's leg consists of an exoskeleton lever powered by two muscles that contract and relax in opposition.
B) A hydrostatic skeleton within the grasshopper's legs allows muscles to push against body fluids.
C) An antagonistic pair of muscles pull in opposite directions around a joint connecting two pieces of cartilage in the grasshopper's leg.
D) There are two muscles within the leg portion of the grasshopper's exoskeleton,one that pushes and one that pulls.
E) Hydrostatic pressure that builds up inside the grasshopper's leg is released rapidly.

Question 35

Which event occurs immediately before the power stroke that moves actin and myosin filaments past one another?

A) Calcium is released from the sarcoplasmic reticulum.
B) ATP binds to myosin.
C) Myosin heads bind to actin.
D) Calcium binds to troponin.
E) Myosin releases phosphate ion.

Question 36

Exoskeletons of lobsters are composed of

A) chitin and calcium-containing minerals.
B) collagen and calcium-containing minerals.
C) chitin and cartilage.
D) collagen and cartilage.
E) chitin,collagen,and calcium-containing minerals.

Question 37

An advantage of an endoskeleton over an exoskeleton is that an endoskeleton

A) provides muscle attachment sites.
B) provides protection.
C) grows as the animal grows.
D) supports the animal's weight.
E) gives structure to the animal.

Question 38

Which statement about skeletal systems is true?

A) An exoskeleton consists mostly of cartilage.
B) A hydrostatic skeleton cannot be used for locomotion.
C) An exoskeleton can continue to grow once it is laid down.
D) An external skeleton must remain flexible,so it never includes calcium-containing minerals,as bones do.
E) Bones in an endoskeleton are constantly undergoing change and remodeling.

Question 39

Which two animals have different types of skeletal systems?

A) Turtle and crab
B) Flounder and sparrow
C) House fly and crayfish
D) Shark and frog
E) Spider and cricket

Question 40

Protein conformational change is essential during the molecular sequence of events of muscle contraction.If the muscle begins in a relaxed mode and is stimulated to contract by a nerve impulse,what is the correct order of protein conformational changes that will follow?

A) Myosin,troponin,tropomyosin
B) Troponin,tropomyosin,myosin
C) Tropomyosin,myosin,troponin
D) Myosin,tropomyosin,troponin
E) Tropomyosin,troponin,myosin

Question 41

Which represents a similarity between fast- and slow-twitch muscle fibers?

A) Number of mitochondria
B) Amount of myoglobin
C) Activity of glycolytic enzymes
D) Number of neuromuscular junctions
E) Number of blood vessels

Question 42

The three systems by which muscles obtain ATP

A) differ in the capacity and rate at which they produce ATP.
B) rely on the large amounts of ATP stored in muscle.
C) produce similar amounts of ATP.
D) rely on reactions within mitochondria.
E) have similar time courses.

Question 43

In the first 15 minutes of a 10K run,the major energy source of the runner's leg muscles is

A) preformed ATP.
B) glycolysis.
C) oxidative metabolism.
D) pyruvate and lactate.
E) the protein from his diet.

Question 44

Which is not one of the systems that supplies muscles with the ATP needed for contraction?

A) Immediate system
B) Gluconeogenesis system
C) Glycolytic system
D) Oxidative system
E) Both a and c

Question 45

Migrating birds often cross the Gulf of Mexico in a single flight,and their flight muscles demand extreme endurance.An examination of the muscles used to perform this activity would show that they

A) have low reserves of glycogen (metabolic fuel).
B) have high levels of ATPase activity.
C) are well-supplied with blood vessels.
D) have few mitochondria.
E) have low levels of myoglobin.

Question 46

Compared to the legs of sedentary people,the legs of cross-country skiers and long-distance runners are likely to have

A) almost all slow-twitch fibers.
B) almost all fast-twitch fibers.
C) about the same number of slow-twitch and fast-twitch fibers.
D) more slow-twitch fibers.
E) more fast-twitch fibers.

Question 47

Which statement about slow-twitch and fast-twitch muscles is true?

A) The first is smooth muscle and the second is skeletal muscle.
B) They express different genes coding for their myosin molecules.
C) Fast-twitch muscles occur only in mammals.
D) They typically have similar numbers of mitochondria per cell.
E) They both compensate for low ATPase activity by recycling their actin-myosin bridges.

Question 48

If the slow-twitch muscle fibers of a marathon runner,weight lifter,and triathlon competitor (5K run,1K swim,10K bicycle ride)were compared,which would represent the correct order of the percentage of slow-twitch muscle fibers observed in their bodies (from the athlete with the highest percentage to the athlete with the lowest)?

A) Marathon runner,triathlete,weight lifter
B) Weight lifter,marathon runner,triathlete
C) Triathlete,marathon runner,weight lifter
D) Triathlete,weight lifter,marathon runner
E) Marathon runner,weight lifter,triathlete

Question 49

Wild turkeys have breast muscles that are capable of explosively fast flight,but only for short distances.These muscles

A) fuel their rapid flight with high levels of mitochondria.
B) have surprisingly low rates of ATPase activity.
C) contain a high proportion of fast-twitch muscle fibers.
D) contain a high proportion of slow-twitch muscle fibers.
E) have substantial reserves of glycogen.

Question 50

Salmon returning to spawn in their native stream require extreme endurance for the journey.An examination of the muscles used to perform this activity would show that they

A) have low reserves of glycogen (metabolic fuel).
B) have high levels of ATPase activity.
C) are poorly supplied with blood vessels.
D) have few mitochondria.
E) have high levels of myoglobin.

Question 51

Which is a difference between fast-twitch fibers and slow-twitch fibers?

A) Fast-twitch fibers are more common in the leg muscles of champion sprinters than of marathon runners,and the reverse is true for slow-twitch fibers.
B) Fast-twitch fibers have more mitochondria.
C) Fast-twitch fibers fatigue less rapidly.
D) The abundance of fast-twitch fibers is more a product of training than of genetics,and the reverse is true for slow-twitch fibers.
E) Fast-twitch fibers are more common in postural muscles than in finger muscles,and the reverse is true for slow-twitch fibers.

Question 52

Fast-twitch fibers

A) are also called white muscle.
B) fatigue rapidly.
C) have fewer mitochondria per cell compared to slow-twitch fibers.
D) are also called glycolytic muscle.
E) All of the above

Question 53

A characteristic of the glycolytic system for supplying ATP to muscle fibers is

A) the inefficiency of glycolysis compared to aerobic respiration.
B) the long period of time that is required before it can start supplying ATP.
C) the rapid rate at which glycolytic enzymes produce ATP.
D) its ability to supply ATP for extended periods of time.
E) its ability to function in the absence of oxygen.

Question 54

Slow-twitch fibers

A) are also called oxidative muscle.
B) are also called red muscle.
C) are well supplied with mitochondria.
D) contain the oxygen-binding protein myoglobin.
E) All of the above

Question 55

Refer to the graph below showing the capacity of three systems that provide ATP for muscle contraction in humans.Based on the diagram,which statement is true?

A) The system of curve A metabolizes carbohydrates to pyruvate and lactate.
B) The system of curve B comes on line within seconds but lacks sustained efficiency.
C) The system of curve B uses ATP produced by oxidative metabolism.
D) The system of curve C uses preformed ATP and creatine phosphate.
E) The system of curve C enables fast-twitch fibers to generate force quickly.

Question 56

The glycolytic system by which muscles obtain ATP

A) relies on creatine phosphate.
B) is also referred to as the immediate system.
C) is the most efficient means of producing ATP.
D) produces lactic acid.
E) completely metabolizes carbohydrates and fats.

Question 57

Shot-putters competing in track and field events need short,intense bursts of energy,but they tend to be quickly fatigued by the activity.An examination of the muscles used in this sport would show that they

A) have substantial reserves of fuel.
B) have low levels of ATPase activity.
C) are well-supplied with blood vessels.
D) have many mitochondria.
E) can develop tension quickly.

Question 58

Fast-twitch skeletal muscle fibers,called white muscle,are characterized by

A) a high concentration of myoglobin.
B) abundant mitochondria.
C) the rapid development of high tension.
D) the ability to sustain activity for a long time.
E) a higher oxygen requirement than that of slow-twitch fibers.

Question 59

Bricklayers occasionally need to carry stacks of bricks from their truck to the work site;this is a heavy load,but it is only carried a short distance.An examination of the muscles used to perform this work would show that they

A) have substantial reserves of fuel.
B) have low levels of ATPase activity.
C) are well-supplied with blood vessels.
D) have relatively few mitochondria.
E) develop tension slowly.

Question 60

Which statement about fast-twitch and slow-twitch fibers is false?

A) Athletes in different sports show different percentages of slow-twitch muscle fibers.
B) Differences in the amount of myoglobin and number of mitochondria contribute to the differences in the color of fibers.
C) A single muscle may contain fast- and slow-twitch fibers.
D) Fast-twitch fibers fatigue slowly.
E) The proportion of fast-twitch and slow-twitch fibers in muscle can be altered using different types of athletic training.

Question 61

To maintain high efficiency and greater power output with increasing wing beat frequencies,insect flight muscles have evolved

A) a high ratio of muscle contractions to excitation events.
B) a high ratio of actin to myosin.
C) a nonsliding filament contraction mechanism.
D) fast T tubules.
E) gap junctions.

Question 62

A biologist studying the electric organ in a fish species observes very little actin or myosin in the cells,even though they are known to have evolved from muscle cells.Several hypotheses have been proposed to account for this observation.Which hypothesis is the most probable?

A) The genes for actin and myosin have been lost from the chromosomes in these cells.
B) The cells actively degrade actin and myosin at a higher rate than muscle cells do.
C) The cells transport actin and myosin out into the extracellular space.
D) The genes for actin and myosin are expressed at a much lower level than they are in muscle cells.
E) Actin and myosin are modified by the cells to an extent that they lose their identification as actin or myosin.

Question 63

"_______" is the term used for the state of the adductor muscle of a mollusk as it maintains a contraction for an extended period of time.

A) Fix
B) Catch
C) Seal
D) Intercalate
E) Latch

Question 64

Cardiac muscle differs from both smooth and skeletal muscle in that

A) its actin and myosin show no repeating pattern of arrangement when viewed under a microscope.
B) neighboring cells in cardiac muscle are electrically coupled by gap junctions.
C) its contractions are not explained by the sliding filament theory of muscular contraction.
D) contractions of cardiac muscle are not due to Ca²⁺ influx into the sarcoplasm.
E) its cells are multinucleated.

Question 65

Which type of muscle cell is shown in the image below?

A) Skeletal
B) Cardiac
C) Smooth
D) Insect flight muscle
E) Both a and d

Question 66

Smooth muscle differs from both cardiac and skeletal muscle in that

A) it can act as a pacemaker for rhythmic contractions.
B) contractions of smooth muscle are not due to Ca²⁺ influx into the sarcoplasm.
C) neighboring cells in smooth muscle are electrically coupled by gap junctions.
D) neighboring cells in smooth muscle are tightly connected by intercalated discs.
E) its actin and myosin show no repeating pattern of arrangement when viewed under a microscope.

Question 67

Which structure uses smooth muscle contractions to function?

A) Heart
B) Tongue
C) Eyelid
D) Knee
E) Bladder

Question 68

Which structure is absent in cells of a fish electric organ?

A) Sarcomere
B) Nucleus
C) Mitochondria
D) Neuromuscular junction
E) Both a and d

Question 69

The figure below shows an electron micrograph of a portion of one insect flight muscle cell.Identify the structures labeled A and B.

A) A = actin and myosin filaments;B = gap junctions
B) A = T tubules;B = sarcoplasm
C) A = actin and myosin filaments;B = mitochondria
D) A = T tubules;B = mitochondria
E) A = sarcoplasm;B = gap junctions

Question 70

Which statement about sarcomeres is true?

A) Sarcomeres are present in cardiac and skeletal muscle,but absent in smooth muscle.
B) Sarcomeres are present in smooth and skeletal muscle,but absent in cardiac muscle.
C) Sarcomeres are present in smooth and cardiac muscle,but absent in skeletal muscle.
D) Sarcomeres are present in skeletal muscle but absent in smooth and cardiac muscle.
E) Sarcomeres are present in all types of muscle.

Question 71

Which statement about smooth muscle is true?

A) Smooth muscle is not under nervous system control.
B) Smooth muscle cells are multinucleated.
C) Smooth muscle appears striated when viewed with the microscope.
D) Gap junctions are uncommon in smooth muscle.
E) Actin and myosin are responsible for the contraction of smooth muscle.

Question 72

If a defect occurs in a developing human fetus that stops the transmission of signals between cells in cardiac muscle,which structure is most likely involved?

A) Myosin
B) Intercalated discs
C) Mitochondria
D) T tubules
E) Sarcoplasmic reticulum

Question 73

Regarding skeletal,smooth,and cardiac muscle cells,which structure(s)is/are present in all three types?

A) Sarcomere
B) Sarcoplasmic reticulum
C) Gap junctions
D) Intercalated discs
E) Striations

Question 74

A biologist is looking at human muscle fibers under the microscope.Which criterion should the biologist use to distinguish between skeletal and cardiac muscle fibers?

A) Presence or absence of T tubules
B) Presence or absence of regular arrays of thick and thin filaments
C) Number of mitochondria
D) Number of cell nuclei
E) Presence or absence of a sarcoplasmic reticulum

Question 75

A biologist is looking at human muscle fibers under the microscope.Which criterion should the biologist use to distinguish between cardiac and smooth muscle fibers?

A) Number of cell nuclei
B) Presence or absence of a sarcoplasmic reticulum
C) Presence or absence of regular arrays of thick and thin filaments
D) Presence or absence of actin and myosin
E) Presence or absence of gap junctions