Science E-Learning: Chapter 6: Movement (Hydrostatic skeleton and the function of endoskeleton)

Content standard:

Support, movement and growth in animals

Learning standard:

Relate hydrostatic skeleton with movement

Elaborate the function of endoskeleton in animals

Lesson activity:

Welcome back! Today we are going to learn how hydrostatic skeleton bring about movement and the function of endoskeleton in animals.So first, let's talk about hydrostatic skeleton. Do you still remember examples of animals that have hydrostatic skeleton?If you did the previous exercise (powerpoint presentation), i believe you still remember. So, before we discuss about the movement of hydrostatic skeleton, let's watch this video.

In earthworms, the skeleton consists of pressurized fluid within a cavity in the body known as the coelom. The coelom extends throughout the body and is separated into many segments. Although the segments are interconnected, the worm is able to move them independently.Surrounding the fluid-filled coelom are two sets of muscles. Circular muscles wrap around each segment, and longitudinal muscles extend across the length of the body. These muscles are powerful and well-developed. The circular and longitudinal muscles work together to help the earthworm writhe, wiggle and push its way through the substratum of soil.Worms are also covered in short, bristly hairs called chaetae. The chaetae are normally held inside the earthworm's body, but they are extended when the worm is burrowing or anchoring itself in the soil. These chaetae act as an anchor so that the worms can then pull the rear part of their bodies forward. Diagram below shows how the earthworms look like when longitudinal muscles and circular muscles contract.

Diagram 1: The longitudinal muscles and circular muscles

Diagram 2: The "must have" parts in earthworms to able them to move.

Ok. Watch this video to understand more the movement of earthworm.

Next, let's discuss the function of endoskeleton in vertebrates animals. The endoskeleton of vertebrates is an internal scaffolding to which muscles attach and against which they can pull. Vertebrates animals can be divided into three which are land vertebrates, aquatic vertebrates and birds. The function of the endoskeleton in each vertebrates are different depending on their habitat. The entire body of land vertebrates is supported by the endoskeleton. So they have large and strong skeletons.Land vertebrates have a long column of backbone, strong and big pectoral and pelvic girdles to support their body weight. Aquatic vertebrates have very small and weak pectoral and pelvic girdles. A large part of their body is supported by the buoyancy of water. Buoyancy is force from water which allows an object to float.

Diagram 3: The pectoral and pelvic girdle in two different vertebrates.

Birds have hollow bones to enable them to fly. Advantages of hollow bones are light and strong, allow vertebrates to move faster, and require less calcium and phosphorus. That is why birds can move faster than the land vertebrates. Now watch this video.