NCERT Solutions for Class 11 Biology Chapter 17 Locomotion and Movement

NCERT
SOLUTIONS
CLASS - 11th

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Class : 11th
Subject : Biology
Chapter : 20
Chapter Name : Locomotion And Movement

Q1 Draw the diagram of a sarcomere of skeletal muscle showing different regions.

Answer. The diagrammatic representation of a sarcomere is as follows:

Page : 313 , Block Name : Exercise

Q2 De ne sliding lament theory of muscle contraction.

Answer. The sliding lament theory explains the process of muscle contraction during which the
thin laments slide over the thick laments, which shortens the myo bril. Each muscle bre has
an alternate light and dark band, which contains a special contractile protein, called actin and
myosin respectively. Actin is a thin contractile protein present in the light band and is known as
the I-band, whereas myosin is a thick contractile protein present in the dark band and is known as
the A-band. There is an elastic bre called z line that bisects each I-band. The thin lament is
rmly anchored to the z line. The central part of the thick lament that is not overlapped by the
thin lament is known as the H-zone. During muscle contraction, the myosin heads or cross
bridges come in close contact with the thin laments. As a result, the thin laments are pulled
towards the middle of the sarcomere. The Z line attached to the actin laments is also pulled
leading to the shortening of the sarcomere.

Hence, the length of the band remains constant as its original length and the I-band shortens and
the H-zone disappears.

Page : 313 , Block Name : Exercise

Q3 Describe the important steps in muscle contraction.

Answer. During skeletal muscle contraction, the thick lament slides over the thin lament by a
neuromuscular junction or motor end plate. Neuromuscular junction is a junction between a
neuron and the sarcolemma of the muscle bre. As a result, Acetylcholine (a neurotransmitter) is
released into the synaptic cleft by generating an action potential in sarcolemma.
Step 2: The generation of this action potential releases calcium ions from the sarcoplasmic
reticulum in the sarcoplasm
Step 3: The increased calcium ions in the sarcoplasm leads to the activation of actin sites. Calcium
ions bind to the troponin on actin laments and remove the tropomyosin, wrapped around actin
laments. Hence, active actin sites are exposed and this allows myosin heads to attach to this site.
Step 4: In this stage, the myosin head attaches to the exposed site of actin and forms cross bridges
by utilizing energy from ATP hydrolysis. The actin laments are pulled. As a result, the H-zone
reduces. It is at this stage that the contraction of the muscle occurs.
Step 5: After muscle contraction, the myosin head pulls the actin lament and releases ADP along
with inorganic phosphate. ATP molecules bind and detach myosin and the cross bridges are
broken.
Stage 6: This process of formation and breaking down of cross bridges continues until there is a
drop in the stimulus, which causes an increase in calcium. As a result, the concentration of
calcium ions decreases, thereby masking the actin laments and leading to muscle relaxation.

Page : 313 , Block Name : Exercise

Q4 Write true or false. If false change the statement so that it is true.
(a) Actin is present in thin lament
(b) H-zone of striated muscle bre represents both thick and thin laments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body

Answer. (a) True
(b) False
H -zone of striated muscle bre is the central part of the thick lament that is not overlapped by
the thin lament.
(c) True
(d) False
There are 12 pairs of ribs in a man.
(e) True

Q5 Write the difference between :
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle

Answer. (a) Actin and Myosin

(b) Red and White muscles

(c) Pectoral and Pelvic girdle

Q6 Match Column I with Column II :

Answer.

Q7 What are the different types of movements exhibited by the cells of human body?

Answer. Movement is a characteristic feature of living organisms. The different types of movement
exhibited by cells of the human body are:
• Amoeboid movement: Leucocytes present in the blood show amoeboid movement. During tissue
damage, these blood cells move from the circulatory system towards the injury site to initiate an
Immune response.
Ciliary movement: Reproductive cells such as sperms and ova show ciliary movement. The passage
of ova through the fallopian tube towards the uterus is facilitated by this movement.
• Muscular movement: Muscle cells show muscular movement.

Q8 How do you distinguish between a skeletal muscle and a cardiac muscle?

Answer.

Q9 Name the type of joint between the following:-

(a) atlas/axis
(b) carpal/metacarpal of thumb
(c) between phalanges
(d) femur/acetabulum
(e) between cranial bones
(f) between pubic bones in the pelvic girdle

Answer. (a) atlas/axis: Pivotal joint
(b) carpal/metacarpal of thumb: Saddle joint
(c) between phalanges: Hinge joint
(d) femur/acetabulum: Ball and socket joint
(e) between cranial bones: Fibrous joint
(f) between pubic bones in the pelvic girdle: Ball and socket joint

Q10 Fill in the blank spaces:
(a) All mammals (except a few) have __________ cervical vertebra.
(b) The number of phalanges in each limb of human is __________ .
(c) Thin lament of myo bril contains 2 ‘F’ actins and two other proteins namely __________ and
__________.
(d) In a muscle bre (Ca) ++
is stored in __________ .
(e) __________ and __________ pairs of ribs are called oating ribs.
(f) The human cranium is made of __________ bones.

Answer. (a) Seven
(b) 14
(c) Troponin and tropamyosin
(d) sarcoplasmic reticulum
(e) 11th and 12th
(f) eight