NCERT Class 11-Biology: Chapter – 20 Locomotion and Movement Part 6 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 5:

Discuss the role of ions in muscle contraction. Draw neat sketches to illustrate your answer.


The role of ions in muscle contraction are:

(i) Stored calcium ions are released by the sarcoplasmic reticulum which binds into the specific sites of the troponin component of the thin filament.

(ii) This binding causes a change in conformation of the troponin molecule and the active sites which are present on the F-actin molecules become exposed.

(iii) The active sites of F-actin are specific to myosin head which have ATPase activity dependent on .

(iv) is pumped back to the sarcoplasmic reticulum during the relaxation of the muscles.

(v) This causes the masking of active sites of myosin head by the troponin component.

(vi) The muscles get relaxed due to the breaking of cross-bridge and thin filaments occupying their normal position.

Question 6:

Differentiate between Pectoral and Pelvic girdle.


Pectoral and Pelvic Girdle
Pectoral girdlePelvic girdle
(i) It is composed of two bones(i) It is composed of three bones
(ii) It is present in the anterior portion of the body(ii) It is present in the posterior portion of the body
(iii) Glenoid cavity is the articulation(iii) Acetabulum is the articulation point.
(iv) Humerus bone articulates with pectoral girdle(iv) Femur articulates with pelvic girdle
(v) Its function is to help in articulation of bones of fore limbs, lifting etc.(v) Its function is walking, standing, jumping and in articulation of bones of hind limbs

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