Write true or false. If false, change the statement, so that it is true.
a) Actin is present in thin filament.
b) H-zone of striated muscle fibre represents both thick and thin filaments.
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.

Hint: The musculo-skeletal system includes both the muscles and bones present in the body. This organ system helps in providing shape and structure to the body. It comprises various protein, bony structures, and other tissues.

Complete answer:
a) Muscle fibers are made up of two types of myofibril filaments, namely the myosin (or the thick filaments) and action (or the thin filaments). The actin filament is made up of two monomeric strings of globular actin (G-actin) coiled about each other in a right-handed helix. So, the statement is true.
b) In the muscle fiber, the thin and thick fibers are arranged in a peculiar linear structure called the sarcomere. The thick and thin filaments form a pattern of alternating light and dark bands. The light band (I-band) contains only the thin filament. Whereas, the dark band (A-band) contains both thin and thick filaments. The region of a muscle fiber which contains only the myosin (thick filaments) is known as the H zone. Thus, the statement is false.
Therefore, the true statement shall be ‘H-zone of striated muscle fibre represents only the thick filaments.’
c) The skeleton provides an internal framework to the body and protects the vital internal organs. At birth, infants have 270 bones. Later on, these bones fuse and decrease to around 206 in their adult stage. Thus, the statement is true.
d) Ribs are the long curved bones that form the rib cage in humans. In an adult, there are 12 pairs of ribs. These are attached to the vertebral column on the dorsal side and with the sternum on the ventral side of the body. Thus, the statement is false.
Therefore, the true statement shall be ‘There are 11 pairs of ribs in man.’
e) Sternum is the flat bone also known as the ‘breast bone’. It is present on the ventral side of the human body. Thus, the statement is true.

Note:
Musculoskeletal system is responsible for the locomotory functions of the human body. The structures or body tissues of this organ system collectively provide stability and protection to the body as well as its organs.