Support Systems in Animals, Grade 10: The Function of the Skeleton the Summary Leaves Out

The revision summary lists what the skeleton does: move the body, protect and support the organs, store minerals and let us hear.

It leaves out the one that keeps you alive. Bone marrow makes your blood cells. Every red blood cell in your body was made inside a bone.

The teaching pages get it right. They say the red bone marrow forms the red blood cells, and the long bone diagram labels it twice. Then the summary, which is the part a learner revises from, drops it.

This page gives all five units, five places where the printed account is wrong or incomplete, and a 37 mark skeleton activity whose marks do add up, which is worth saying because in this project they usually do not.

Where this fits in the curriculum

Subject Life Sciences
Grade 10
Term 2
Topic Topic 6, Support systems in animals
Units Unit 1 types of skeletons. Unit 2 the human skeleton. Unit 3 joints. Unit 4 human locomotion. Unit 5 diseases that affect the skeleton
Formal assessment None. The skeleton investigation is a 37 mark activity
Marks Our worksheet is 80

Finding 1: the functions of the skeleton, without the one that makes blood

"The skeleton allows the body to move, protects and supports internal organs, stores minerals and enables us to hear."

Function In the summary
Movement, by giving muscles something to pull against Yes
Protection of the brain, spinal cord, heart and lungs Yes
Support, holding the body up and giving it shape Yes
Storage of minerals, mainly calcium and phosphorus Yes
Hearing, through the three small bones of the middle ear Yes
Making blood cells in the red bone marrow No

The material knows this. The teaching pages say the red bone marrow forms the red blood cells, and the long bone diagram labels the spongy bone as containing red marrow that produces red blood cells. None of it survives the summary.

Learn six functions, not five. A question asking for the functions of the skeleton is worth as many marks as there are functions, and blood cell formation is the one nobody expects a bone to do.

And the hollow shaft is not empty

The summary says long bones have "a hollow shaft of compact bone and ends made of spongy bone", and stops.

Where What is in it What it does
The shaft cavity Yellow bone marrow Stores fat
The spongy bone at the ends Red bone marrow Makes red blood cells

Hollow is doing a lot of work in that sentence. The shaft is a tube because a tube is strong for its weight, and the space inside is not empty.

Finding 2: rickets is not caused by malnutrition

"Rickets is a softening of the bones in children and is usually caused by malnutrition."

Rickets is caused by a shortage of vitamin D, and through it calcium. A child can be eating enough food and still get rickets. A child can be undernourished in every other way and not get it.

What the summary says What is actually true
Cause Malnutrition Too little vitamin D, so too little calcium is absorbed from food
Where vitamin D comes from Not mentioned Mostly made in the skin from sunlight, with some from oily fish, eggs and fortified foods
What to do about it Nothing you could act on Sunlight on the skin, and calcium in the diet

This is the difference between a fact and a useful fact. "Malnutrition" tells a learner nothing they can do. "Your skin makes vitamin D from sunlight, and without it your bones cannot use the calcium you eat" tells them something, and it is also the version that scores.

Finding 3: arthritis in older people, osteoporosis in older women

"Arthritis is a condition that affects the joints in older people."

"Osteoporosis is the thinning and weakening of the bones, mainly in older women."

Both sentences attach a disease to a group of people and leave out what the disease actually is.

What it is Who gets it
Arthritis Inflammation of a joint, which damages the cartilage and makes movement painful and stiff Most common in older people, and children get it too. Rheumatoid arthritis often starts between thirty and fifty
Osteoporosis Loss of bone density, so the bones become porous and break easily Most common in women after menopause, and men get it as well

The useful distinction is that one is a joint disease and the other is a bone disease. Arthritis attacks the cartilage in a joint. Osteoporosis attacks the bone itself. A learner who has only "older people" and "older women" cannot tell them apart at all.

Finding 4: antagonistic muscles with no example

"Muscles act in antagonistic pairs. When one muscle contracts, the other muscle relaxes."

Correct, and no pair is named anywhere in the summary. The mark is almost always in the example.

Movement Contracts Relaxes
Bending the arm at the elbow Biceps Triceps
Straightening the arm Triceps Biceps

The reason a pair is needed at all is worth one sentence: a muscle can only pull, never push. To move a bone back the other way, a second muscle has to pull it from the opposite side.

Finding 5: the sliding filament explanation is good, and stops one step short

The summary handles the hard part well. "When a skeletal muscle contracts, the actin filaments in the myofibrils slide inwards between the myosin filaments. This causes the sarcomeres to become shorter."

That is correct and it is more than most Grade 10 accounts manage. The filaments themselves do not shorten, which is exactly the thing learners get wrong.

What is missing is the last line: when every sarcomere shortens, the whole muscle shortens, and the bone it is attached to moves. Without it the explanation stops inside the cell and never reaches the arm.

Level What happens
Filament Actin slides between myosin. Neither filament gets shorter
Sarcomere The ends are pulled in, so the sarcomere shortens
Myofibril Thousands of sarcomeres in a row, all shortening at once
Muscle The whole muscle shortens and pulls on the tendon
Bone The tendon pulls the bone and the joint moves

The activity that does add up

The skeleton investigation is printed at 37 marks and its fifteen allocations add to 37.

We say so because this project has now checked a lot of printed tasks and the arithmetic usually fails. Three Grade 11 assessed tasks in a row did not add up. This one does, and that deserves saying as plainly as the failures.

Question Marks
Skull: shape, why joined tightly, the foramen magnum 3
Lower jaw: name and why it moves 2
Vertebral column and ribs: five counts 5
Name the bones of the pectoral girdle and arm 8
Name the bones of the pelvic girdle and leg 9
Largest bone, and why it is large 2
Flat, long, irregular and short bones, for both skeletons 8
Total 37

Seventeen of the 37 marks are naming bones. If a class has one skeleton to look at, that is where the lesson time goes.

What the five units cover

Unit What is in it
1. Types of skeletons Hydrostatic in soft-bodied animals, exoskeletons of chitin in arthropods, endoskeletons of bone in vertebrates
2. The human skeleton Functions, bone and cartilage, ligaments and tendons, the axial and appendicular skeletons, long bone structure
3. Joints Fibrous, cartilaginous and synovial, then ball-and-socket, hinge, pivot and gliding
4. Human locomotion Bones, muscles, joints, tendons and ligaments, then skeletal muscle structure and the sliding filament idea
5. Diseases Arthritis, rickets and osteoporosis

The three that get mixed up every year

Term What it joins
Ligament Bone to bone, across a joint
Tendon Muscle to bone
Cartilage Not a joiner at all. It covers the bone ends so they slide instead of grinding

Ligament and limb both start with L and both are about bones. Tendon and muscle both have an M sound in the middle. Whatever gets you there.

What this topic costs

This is the first Life Sciences topic in the project where we can genuinely supply the lesson, and the first where a skeleton is actually on the shelf.

Item Price In stock For
Skeletal muscle slide, transverse section R29,00 29 Unit 4 under a microscope for the price of a loaf of bread. Striations, myofibrils, the lot
Knee joint model R900,00 2 A hinge joint, in the hand
Shoulder joint model R895,00 2 A ball-and-socket joint, next to the knee for the comparison
Elbow joint model R900,00 2 Where the biceps and triceps argument happens
Human skeleton, 170 cm, showing nerves R7 500,00 3 The model the 37 mark activity asks for
Human skeleton with ligaments, 170 cm R13 000,00 1 The same thing with the ligaments shown, which Unit 2 needs

Two skeleton lines we also list are out of stock, at R7 500,00 and R15 559,50, and the 3 part skull model is at zero as well. We are not linking you to any of them.

If the budget is R29, buy the muscle slide. It is the only thing in this topic that a learner cannot get from a diagram, and a class set of thirty costs R870. The skeleton can be a wall chart and a photocopy; the striations cannot.

Microscopes at microscopes.

What you should be able to do by the end

  • Give six functions of the skeleton, blood cell formation included
  • Compare hydrostatic, exo and endoskeletons with an animal for each
  • Split the skeleton into axial and appendicular and name the bones of each
  • Label a long bone, including both marrows and what each one does
  • Tell ligament, tendon and cartilage apart
  • Classify a joint as fibrous, cartilaginous or synovial, then by its movement
  • Explain antagonistic muscle action with a named pair, and say why a pair is needed
  • Explain contraction from filament to bone without saying the filaments shorten
  • Say what arthritis, rickets and osteoporosis actually are, and what causes rickets

Free worksheet and marking memo

Both free, no sign up, straight to the PDF.

Related practicals