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Biology - The human skeleton and muscular system

Grade 4IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The human skeleton provides three main functions: support for the body, protection of vital organs, and allowing movement through joints.

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The skeleton protects delicate organs: the skull protects the brain, and the rib cage protects the heart and lungs (O2O_2 and CO2CO_2 exchange centers).

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Joints are places where two bones meet. Hinge joints (like the elbow) allow back-and-forth movement, while ball and socket joints (like the shoulder) allow circular movement.

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Muscles are attached to bones by tendons. They move bones by contracting (shortening) and relaxing (lengthening).

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Muscles work in antagonistic pairs. For example, to bend the arm, the biceps contract while the triceps relax.

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Bones are living tissues that require minerals like Calcium (Ca2+Ca^{2+}) and Phosphorus (PP) to remain strong and healthy.

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The spine is made of small bones called vertebrae, which protect the spinal cord and allow the body to bend.

📐Formulae

C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy}

Muscle Work=Force×Distance\text{Muscle Work} = \text{Force} \times \text{Distance}

Bone Mineral Density=Bone Mineral Content (g)Area (cm2)\text{Bone Mineral Density} = \frac{\text{Bone Mineral Content (g)}}{\text{Area (cm}^2\text{)}}

💡Examples

Problem 1:

Explain how the biceps and triceps work together to straighten the arm.

Solution:

The triceps contract while the biceps relax.

Explanation:

Because muscles can only pull and not push, they must work in pairs. To straighten the arm, the tricep muscle on the back of the arm shortens (contracts) to pull the bone down, while the bicep on the front lengthens (relaxes).

Problem 2:

Which organ does the rib cage protect, and which gas is primarily absorbed there?

Solution:

The rib cage protects the lungs; the gas absorbed is Oxygen (O2O_2).

Explanation:

The rib cage forms a protective 'cage' around the thoracic cavity. Inside, the lungs facilitate the intake of O2O_2 into the bloodstream and the removal of CO2CO_2 waste.

Problem 3:

If a bone has a mineral content of 10g10g and an area of 5cm25cm^2, calculate its density using the provided formula.

Solution:

2g/cm22g/cm^2

Explanation:

Using the formula 10g5cm2=2g/cm2\frac{10g}{5cm^2} = 2g/cm^2, we find the concentration of minerals like Ca2+Ca^{2+} in that section of the bone.

The human skeleton and muscular system Revision - Grade 4 Science IGCSE