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.
(a) Muscle fibres are composed of myofibrils. The filaments of myofibrils consist of two types, thick and thin. The thick filaments are made of the protein myosin. The thin filaments are made of the protein actin. So, the statement is true. (b) The region of a striated muscle fibre that contains only thick (myosin) filaments is the H-zone. It appears as a lighter band in the middle of the dark A-band at the centre of a sarcomere. So, the statement is false. H-zone of striated muscle fibre represents thick filament. (c) The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth which decreases to around 206 bones by adulthood after some bones get fused together. So, the statement is true. (d) Ribs are the long curved bones that form the rib cage. They protect the lungs, heart, and other internal organs of the thorax. There are 24 ribs in the human body, divided into two sets of 12 curved, flat bones. So, the statement is false. There are 12 pairs of ribs in man. (e) The sternum or breastbone is a long flat bone shaped located in the center of the chest. It lies at the anterior (ventral) middle part of the chest. So, the statement is true.
