krit.club logo

Living Things - Human Body Systems (Digestive, Skeletal, and Muscular)

Grade 4IB

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

🔑Concepts

The Digestive System is responsible for breaking down food into nutrients like glucose (C6H12O6C_6H_{12}O_6) which the body uses for energy.

Mechanical digestion occurs in the mouth (teeth) and stomach, while chemical digestion uses enzymes and acids (HClHCl) to break down food molecules.

The Skeletal System provides a structural framework, protects internal organs, and stores minerals like Calcium (Ca2+Ca^{2+}).

Bones meet at joints, which allow for different types of movement (e.g., hinge joints in the knee, ball-and-socket joints in the shoulder).

The Muscular System consists of over 600 muscles. Skeletal muscles work in 'antagonistic pairs'—when one muscle contracts (shortens), the other relaxes (lengthens) to move a bone.

The body maintains homeostasis, ensuring that all systems work together to keep the internal environment stable.

📐Formulae

Total Adult Bones=206\text{Total Adult Bones} = 206

Food+EnzymesNutrients+Waste\text{Food} + \text{Enzymes} \rightarrow \text{Nutrients} + \text{Waste}

Movement=Muscle Contraction+Bone Lever\text{Movement} = \text{Muscle Contraction} + \text{Bone Lever}

💡Examples

Problem 1:

If a person has 206206 bones in their adult body, but a baby is born with approximately 300300 bones, what process explains this change?

Solution:

300206=94300 - 206 = 94 bones 'disappear' through fusion.

Explanation:

As a human grows, many smaller bones fuse together to form larger, stronger bones. This is why an adult has fewer individual bones than an infant.

Problem 2:

Explain how the biceps and triceps work together to lift a heavy book.

Solution:

Bicep (Contracted) + Tricep (Relaxed) = Arm Flexion.

Explanation:

Muscles can only pull, not push. To lift the book, the bicep on the front of the upper arm contracts (gets shorter and tighter), while the tricep on the back relaxes. To lower the arm, the tricep contracts and the bicep relaxes.

Problem 3:

In which part of the digestive system does the most nutrient absorption occur?

Solution:

The Small Intestine.

Explanation:

While the stomach breaks down food into a liquid called chyme, the small intestine is where nutrients like vitamins, minerals, and glucose (C6H12O6C_6H_{12}O_6) are absorbed into the bloodstream through tiny finger-like projections called villi.

Human Body Systems (Digestive, Skeletal, and Muscular) Revision - Grade 4 Science IB