Class 11 Biology Chapter 16 Skeleton and Movements Textbook solutions
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1. Choose the correct option
A. The functional unit of striated muscle is
…………..
a. cross bridges
b. myofibril
c. sarcomere
d. z-band
B. A person slips from the staircase and
breaks his ankle bone. Which bones are
involved?
a. Carpals
b. Tarsal
c. Metacarpals
d. Metatarsals
C. Muscle fatigue is due to accumulation of
……..
a. pyruvic acid
b. lactic acid
c. malic acid
d. succinic acid
D. Which one of the following is NOT
antagonistic muscle pair?
a. Flexo-extensor
b. Adductor-abductor
c. Levator-depressor
d. Sphinetro-suprinater
E. Swelling of sprained foot is reduced by
soaking in hot water containing a large
amount of common salt,
a. due to osmosis
b. due to plasmolysis
c. due to electrolysis
d. due to photolysis
F. Role of calcium in muscle contraction
is ……….
a. to break the cross bridges as a cofactor in the hydrolysis of ATP
b. to bind with troponin, changing its shape so that the actin filament is
exposed
c. to transmit the action potential across the neuromuscular junction.
d. to re-establish the polarisation of the plasma membrane following an action potential.
G. Hyper-secretion of parathormone can
cause which of the following disorders?
a. Gout
b. Rheumatoid arthritis
c. Osteoporosis
d. Gull’s disease
2. Answer the following questions
A. What kind of contraction occurs in your neck muscles while you are reading your class assignment?
Answer : Use over-the-counter pain relievers such as aspirin, ibuprofen (Motrin), naproxen (Aleve), or acetaminophen (Tylenol).
Apply heat or ice to the painful area. …
Apply heat using warm showers, hot compresses, or a heating pad.
To prevent injuring your skin, do not fall asleep with a heating pad or ice bag in place.
B. Observe the diagram and enlist importance of ‘A’, ‘B’ and ‘C’.
Answer :
A – Anterior portion
B- posterior portion
C- Facet for articulation
with occipital condyle
C. Raju intends to train biceps; while
exercising using dumbbells, which joints
should remain stationary and which should move?
Answer : —————-
D. In a road accident, Moses fractured his leg. One of the passers by, tied a wodden plank to the fractured leg while Moses was rushed to the hospital Was this essential? Why?
Answer : Yes, it was essential.
Explanation: The explanation is that after moses’ leg was fractured it was in a critical situation as movement would have enlarged the fractured area and would have made it worse. But after tying his leg to a plank the passer-by ensured that his leg was now in a more stable condition than and the broken fragments of bone couldn’t move now.
E. Sprain is more painful than fracture. Why?
Answer : Sometimes, a sprain can be even more painful than a break. A sprain is caused by trauma that overstretches ligaments and puts stress on a joint. A mild sprain is where the ligaments are stretched but the joint remains stable, while a moderate sprain is where the ligaments are slightly torn, making the joint unstable.
F. Why a red muscle can work for a prolonged period whereas white muscle fibre suffers from fatigue after a shorter
work?
Answer : Since red muscle fibers have much better capillary supply and a greater number of mitochondrion which is responsible for ATP supply to the muscle cell, therefore they are specialized for sustained work. On the other hand, white muscle cells have less capillary, fewer mitochondria, so they do not have such good supply as the red cells. White cells have lots of glycogen stored, which is quickly accessible and they can produce more force when the need arises, but when that glycogen is depleted you feel muscle tiredness and it takes much longer time for the muscle to recover.
3. Answer the following questions in detail
A. How is the structure of sarcomere suitable for the contractility of the muscle? Explain its function according to sliding filament theory. (Refer to chapter animal tissues.)
Answer : There are 2 major kinds of proteins in muscles. Actin and myosin. Myosin proteins have portions named head that can interact with actin filaments. When calcium enters the cell after some reactions the active sites of actin are ready for the head of the myosin. Head of the myosin uses an ATP molecule and perform a stroke resulting in sliding of actin over myosin towards the centre. This result in shortening of sarcomere resulting in contraction. Thus according to this sliding theory actin and myosin helps in muscle contraction and help in the movements of joints.
B. Ragini, a 50 year old office goer, suffered hair-line cracks in her right and left foot in short intervals of time. She was worried about minor jerks leading to hair line cracks in bones. Doctor explained to her why it must be happening and prescribed medicines.
What must be the cause of Ragini’s problem? Why has it occurred? What precautions she should have taken earlier? What care she should take in
future?
Answer : ————
C. How does structure of actin and myosin help muscle contraction?
Answer :
According to this theory, interaction
between actin and myosin is the basic cause of muscular contraction. Actin filaments are interdigitated with myosin filaments. (like the crossing of fingers of two hands)
The head of the myosin is joined to
the actin backbone by a cross bridge forming a hinge joint. From this joint, head can not tilt in forward and backward directions. This movement is an active process which requires use of ATP.
Myosin head contains ATPase activity.
It can derive energy by the breakdown of ATP molecule. This energy can be used for the movement of myosin heads.
During contraction process, the myosin
heads gets attached to the active site of actin filaments and pull them inwardly, so that actin filaments slide over the myosin filaments. This results in the contraction of muscle fibre.
D. Justify the structure of atlas and axis vertebrae with respect to their position and function.
Answer :
Atlas vertebrae : This is a ring like 1st cervical vertebra. It consists of anterior and posterior arches. It does not have centrum and spinous process. Transverse processes and transverse foramina are large. Vertebral foramen is large and divided into two parts by transverse ligament. Spinal cord passes through anterior
compartment. Anterior zygapophyses, are
replaced by facets for attachment with occipital condyle of skull that forms ‘Yes Joint’.
Axis vertebra : This is the second cervical
vertebra. Centrum of this vertebra gives out tooth-like ‘Odontoid Process’. This process fits into the anterior portion of vertebral foramen of Atlas vertebra forming pivot joint, also called ‘No joint’.
E. Observe the blood report given below
and diagnose the possible disorder.
Answer : The diagnosis can be of Chronic Kidney Disease and a differential diagnosis of Gout. The further confirmation can be done with the help of history of the patient.
4. Write short notes on following points
A. Actin filament
Answer : Actin filament :
It is also a complex type of contractile
protein. It consists of three different components.
i. F actin : It forms the backbone of actin
filament. It is double stranded protein. Each strand is composed of polymerized G actin
molecules. One ADP molecule is attached
to each G actin molecule.
ii. Tropomyosin : The actin filament contains two additional protein strands that are polymers of tropomyosin molecules. Each strand is loosely attached to an F actin. In the resting stage, tropomyosin physically covers the active binding sites for myosin of the actin strand.
iii. Troponin : It is a complex of three
globular proteins, which are attached
approximately 2/3 rd distance along each
tropomyosin molecule. It has affinity for
actin, tropomyosin and calcium ions. The
troponin complex is believed to attach the
tropomyosin to the actin. The strong affinity of troponin for calcium ions is believed to
initiate the contraction process.
B. Myosin filament
Answer : Myosin filament :
Each myosin filament is a polymerized
protein. Many monomeric proteins called
meromyosins constitute one thick filament.
Myosin molecule consists of two heavy chains (heavy meromyosin/HMM) coiled around each other forming double helix. One end of each of these chains is projected outwardly. It is known as cross bridge. This end is folded into a globular protein mass called myosin head.
Two light chains are associated
with each head (Total 4 light chains/light
meromyosin/LMM). Myosin head has a
special ATPase activity. It can split ATP to
produce energy. Myosin contributes 55% of
muscle proteins.
C. Role of calcium ions in contraction and relaxation of muscles.
Answer : These calcium ions interact with
troponin molecules. This interaction inactivates troponin-tropomyosin complex. This leads to change in the structure of tropomyosin. As a result, it gets detached from the active site of actin (F actin) filament. Thus active site becomes uncovered. Now head of
the myosin cleaves the ATP and derives energy. Using this energy, myosin gets attached to the uncovered active site of actin and results in the formation of actomyosin complex. The myosin heads are now tilted backwards and pull the attached actin filament inwardly. This results in contraction of the
muscle fibres.
5. Draw labelled diagrams
A. Synovial joint.
B. Different cartilagenous joints.
