1. Bellwork: Why are skeletons important?

2. Movement and Support
Section 28.2

3. How do animals move?
In order to move animals must generate physical force, and they must apply that force against air, water and land in order to push or pull themselves
Movement is facilitated by rigid body parts
Legs, wings, flippers
Each is supported by some sort of skeleton
There are three main types of skeletons
Hydrostatic, Exoskeletons and Endoskeletons

4. How does a hydrostatic skeleton work?
Fluids held in a gastro vascular cavity that can alter an animal’s body shape drastically
This is done by opening and closing the mouth
When the mouth is closed, water trapped in the body causes the body to elongate
When the mouth is open, water is released and it becomes shorter

5. What does an exoskeleton do?
Many arthropods and mollusks have exoskeleton
A hard body covering made of either chitin (Arthropod) or shell (Calcium carbonate – mollusk)
Jointed exoskeletons allow arthropods to move and live in a variety of ways
Also provides protection
But – there can be issues
Growing is not straightforward
Need to break out of old exoskeleton and build a new one – molting
Exoskeletons are also heavy – can cause issues

6. How does an Endoskeleton work?
Echinoderms and Vertebrates have Endoskeletons
Acts as a structural support system within a body
Sea stars and echinoderm have endoskeleton made of calcified plates
Support and protect, and give a bumpy texture
Vertebrate endoskeletons are made of cartilage, or cartilage and bone
Sharks and other fishes mainly cartilage
Vertebrates bone is most common
Some four limb vertebrates have limb girdles – support limbs and allow animal movement
All provide strong lightweight support, and can grow with the animal

7. What is the importance of joints?
Without joints animals cannot move
A joint is a place where parts of a skeleton are held together in ways that enable them to move in respect to one another
In vertebrates ligaments connect bones at joints
Most joints are a combination of ligaments, cartilage and lubricating fluid

8. How do muscles enable movement?
Muscles are specialized tissues that produce force by contracting when stimulated
But muscles can not actively get longer. Force is only generated in one direction What problem does this cause, how do our bodies address this?
In most animals muscles work together in pairs or groups attached to different parts of a skeleton
Tendons attach muscles to bones around joints
Tendons pull on bones when muscles contract

9. So how do the muscular and skeletal system work together?
There is widespread variation amongst vertebrates
In fish and snakes, muscles are arranged in blocks along opposite sides of the backbone
The blocks contract in waves, bending the body from one side to another
Thurst is generated,
Many amphibians look like they are doing pushups, but sideways movement of backbone moves limbs forewards and backwards
Mammal limbs have evolved to enable different kinds of movement

10. Variation explained
Ultimately, the widespread variation to vertebrate musculoskeletal systems allows vertebrates to inhabit a wide range of habitats, and live in a variety of different ways

11. Key Points Questions What body structures generate force?
What are the main advantages and disadvantages of an exoskeleton?
Are endoskeletons always made of bone?
Why are the largest land animals vertebrates?
What characteristics do the skeletons of all vertebrates share?
What connects bones to bones? What connects bones to joints?