How does a skeleton or shell keep things safe inside?
Do humans have shell or frame structures?
How do you make a structure really strong?
Introducing this topic
This is a technology unit and will follow the principles of technology teaching and specifically the design process. As such the different activities in this unit will be preparing learning to build their own shell or frame structure at the end of the unit - these are called
enabling
activities. They are designed to enable learners to tackle the problem at the end of the unit with the necessary knowledge, understanding and skill to complete it confidently.
Learners will have to make a model of a vertebrate skeleton using struts made from rolled paper or drinking straws as a project. Enabling activities in this unit will therefore be:
What is the difference between a shell and a frame structure?
Are there shell and frame structures in nature?
How can a structure be reinforced or made stronger?
What is a strut and how does it make a structure stronger?
Once learners have gained a good understanding of these four points they are required to make a model of a vertebrate skeleton using these skills.
In this chapter we will investigate two kinds of structures, frame and shell structures.
Structures
A structure is something that is arranged or put together in a specific way and is made up of different parts. A jungle gym is an example of a structure. It has many different parts like beams, ropes, and bars, that are put together in a special way.
Most structures are designed to remain stable and rigid which means they should not break and crumble or topple and fall over if something heavy is placed on top of or against them.
Structures have different jobs or functions. They:
support
protect
enclose - that means they keep something in or they keep things from getting in (like a tin of juice or a fence around a building).
help with movement
We get three kinds of structures:
frame structures
shell structures
solid structures
In all structures, the shape of the structure is very important. A structure will be able to resist or hold a certain weight depending on its shape.
In Gr. 4 in Matter and Materials, we looked at strong frame structures and also how to make structures stronger using struts and braces. In this chapter in Life and Living, we are going to focus on two kinds of structures: frame structures and shell structures. This is because they relate to the skeletons of animals.
Turn to a friend and think about the words "Shell Structure" and "Frame Structure" and think what these could mean. Then think of examples of frame structures and of shell structures that you can see in buildings or perhaps on your walk or ride to school. Report back and discuss these with your class.
Teachers can use this question to assess pre-existing knowledge of shell and frame structures as similar work should have been covered in the previous year. Frame structures: burglar bars, palisade fences, cell phone towers, Eskom towers, sieve, jungle gym, etc. Shell structures: tortoise shell, hut, trailer, canopy on a bakkie, eggshell, snail shell, lids, pipes, etc.)
Frame structures
Frame structures are easy to identify because they have a frame or a skeleton. These structures are built or put together by attaching pieces of material together to make a frame. Look at these photos of frame structures.
These photos are all examples of frame structures. In some the frame is clearly visible - these are called open frame structures. In others the frame is covered by a "skin".
Turn to a friend and discuss what you think all these structures have in common - what is the same? Report back to your class.
There are struts and triangle shapes. The frame is sometimes bare and is the whole structure (such as the pyon or jungle gym) or the frame structure is covered by a skin, such as the leaf.
One of the most important frame structures for all vertebrate animals is their skeleton. The material used to make this frame is bone that is attached to the muscles that move the skeleton. The skeleton supports the muscles and protects the organs.
Here is a picture of a human rib cage. Can you see how it makes a frame structure?
The rib cage is a frame structure.
Which organs does the rib cage protect?
The heart, lungs and liver
In general, we can say that all vertebrates have a frame structure as a skeleton. This is because vertebrates have an endoskeleton which supports makes a frame to support the body.
Shell structures
Shell structures generally hold or protect things inside the structure. Humans make shell structures to protect and hold things, like a dish, a tin, a car or house.
In nature, eggshells and the exoskeletons of invertebrates, like crab and crayfish shells, are examples of shell structures. Shell structures are made to resist a very heavy load.
Structures that protect something or hold a weight without breaking or falling, need to be really strong. Let's investigate the different ways we can use to strengthen a structure.
Do you remember in Gr. 4 Matter and Materials when we looked at whether a triangle or a square was stronger? Look at the picture to remind yourself.
Creating a square and a triangle shape.
When you press on the shapes as in the picture, which shape is the most stable and rigid? Explain how you could make the other shape stronger and more stable.
The triangle is the strongest. The square can easily be squashed. You can make the square stronger by putting a diagonal strut in from one corner to the other.
Corners in structures are very important because it is often the weakest point of a structure. To strengthen corners you can:
Put another support (called a brace) across a rectangle's corner to make a triangle. This makes the corner much stronger.
A diagonal brace on a corner where two pieces of wood meet
Place a triangular patch over the corner. This is called a gusset.
Another way of strengthening a corner so it can't collapse, called a gusset.
Making and designing a skeleton
This is the first time learners are doing a Technology project in Grade 5. They will have done some projects in Gr. 4, but it will be useful to emphasise the Design Process again as you are going through the project. The first step is to identify a need to do a design. In this case, a scenario has been set up that the local museum is looking for models of skeletons to put on display and Farrah has a suggestion for the Gr. 5 class to build their own models as you have just been learning about skeletons as structures. Use this to generate the need for doing the design and making the model. At the end you can make a "display" on one side of the classroom as if it is the museum and place the models on display with name tags for each skeleton.
The pattern followed for Technology projects is IDMEC:
Istands for Investigating the problem which some people have, investigating existing products, and investigating concepts and skills that you will need to solve the problem. In this case you would have already done a lot of investigating prior to the activity when first looking at animal skeletons and then at structures and ways to strengthen structures. Learners must use this knowledge and experience when doing their designs.
Dstands for Designing. That means using what you learned from investigations to think of good ways to solve the problem. Remember that learners may come up with new designs for their skeleton as they are going through the project. Encourage them that modifications are allowed and that they should not scrap the original idea but show how their idea has progressed and changed and why they might have changed their design.
Mstands for Making. When you make your model, you use the materials and tools specified to make the model according to the design. Notice that most children design with their hands, not only with pencil and paper. As they work with materials they get more ideas, and their design improves. So we should think of designing and making as more or less the same stage of a project.
Estands for Evaluating. After you have made the model of a skeleton, you need to evaluate it to see if it followed the specifications, for example, can it stand up by itself? Is the model 3D and realistic? Is it a stable structure? Are there any improvements to be made?
Cstands for Communicating. Learners must show other people how they decided on their solution to the problem. The learners should be drawing and writing all through the project. Don't leave the writing to the end, because they find it boring at that stage. When they are getting new ideas they often enjoy writing because they are writing about their own ideas; this is a great strength of technology in school. A technology project gives the children reasons for reading and reasons for writing. And so we can address the literacy problem through the subject of science and technology.
The local museum has asked your school if they have any models of vertebrate skeletons for a display. Farrah has an idea. She loves making things and she also loves animals. So, Farrah has suggested making our own animal skeleton models. We can then better understand the idea of skeletons as structures and use these models to put on display.
Can we make our own animal skeletons?
As a project, you need to design and make a skeleton for a vertebrate. This will be a frame structure.
You may use the following materials:
Drinking straws
Rolled up paper for members and struts.
Wooden dowels or sticks (30cm x 10 mm)
Cellotape
Metal paper fasteners
INVESTIGATE:
Let's investigate and do some research around how to build a shell or frame structure. We looked at different ways to strengthen structures using special shapes and struts. Remember this when you are investigating and designing your skeleton.
DESIGN:
Now you need to use the information we found out to come up with a design for your skeleton. Your skeleton should have the following specifications:
It must be 3-dimensional
It must look realistic
It must have/show the basic parts, i.e. skull, backbone, ribs
It must be strong and rigid and so it can stand on its own
Your design has the following constraints:
You cannot make your skeleton at home - you must make it at school.
You are confined to using some of the following tools and materials: waste paper (A4 and A3), card, brass paper fasteners, glue, scissors, sosatie sticks and nails (to make holes).
Once you have thought about these specifications, you need to answer these questions:
What do you need to design?
What will the size and shape of your skeleton be? Remember that your skeleton must stand up straight for at least 3 minutes.
What materials are you going to use to build your skeleton. Make a list of all the materials you will need.
What tools are you going to need to make your skeleton?
Are there any other specifications and constraints that you can think of for your skeleton?
Now you need to draw some designs for your skeleton. Use scrap pieces of paper to do your first designs. Once you are happy with your design, use the space below to draw your final design. Label your drawing showing what materials you are going to use for the different parts.
MAKE:
Now comes the fun part! You have to make your skeleton according to your sketch and using the materials you identified. Do this in class.
Once you have all finished making your skeletons, you need to show your classmates what you made and tell you what you did to make your skeleton. This is called presenting your design.
EVALUATE:
Answer the following questions about your skeleton.
Did your skeleton stand up for 3 minutes without your support?
What could you change in your skeleton to make it work better?
Did your skeleton fulfill all the requirements in the specifications given to you?
If you ever had to build this skeleton again, what would you do differently?
COMMUNICATE:
An important part of the Design Process is to communicate what you found to others so they can learn from what you did.
Write a paragraph below where you tell Farrah about the skeleton that you built, what worked and what did not work, so that she can also learn from what you did and also build a model skeleton to put on display at the museum.
Structures can be shaped as a shell or frame.
Structures have specific functions - to protect, support, enclose or help to move.
Shell and frame structures in nature.
Structures can be strengthened.
Struts can strengthen structures.
Complete the following table by stating whether the structures are frame or shell structures.
Structure
Shell or frame structure?
Jungle gym
Eggshell
Dog skeleton
Acellphone tower
Acrab skeleton
Scaffolding
Acar
Abasket holding fruit
Structure
Shell or frame structure?
Jungle gym
Frame
Eggshell
Shell
Dog skeleton
Frame
Acellphone tower
Frame
Acrab skeleton
Shell
Scaffolding
Frame
Acar
Shell
Abasket holding fruit
Shell
How would you strengthen a square shape? Give two different ways.
Place a diagonal strut across from one corner to the next. Or put a gusset on the corners.
Give two examples of animals with skeletons that are frame structures. What is the name given to this type of skeleton?
Endoskeletons - dog, human, birds, fish, etc
Give two examples of animals with skeletons that are shell structures. What is the name given to this type of skeleton?
Exoskeletons - crab, insect, etc
What are the advantages to humans for having a frame structure as a skeleton? Explain your answer.
Frames provide support for the muscles for movement. The frame provides protection to the internal organs. The frame structure does these while allowing the human to still grow as the bones are on the inside (endoskeleton). This means humans do not need to get a new skeleton when they grow as animals with exoskeletons do.
