Evan-Moor Daily Science, Grade 5 | EMC5015 - Free Printable

Solution to the Weekly Question: "Why are bones hard and muscles soft?"

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#### A. Describe two ways that bone cells and muscle cells are alike and two ways they are different.

Alike:
1. Both are types of body cells: Bone cells (osteocytes) and muscle cells (myocytes) are both specialized human cells that play essential roles in the body’s structure and function.
2. Both contain a nucleus and cytoplasm: Like all eukaryotic cells, they have a nucleus (which holds genetic material) and cytoplasm (the gel-like substance inside the cell).

Different:
1. Shape and structure: Bone cells are star-shaped with thin extensions, while muscle cells are long, cylindrical, and often striated (striped), especially in skeletal muscle.
2. Function: Bone cells help form and maintain hard bone tissue, providing support and protection. Muscle cells contract and relax to produce movement.

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#### B. Why do you think nutrition experts recommend that young people eat foods high in calcium?

Nutrition experts recommend that young people eat foods high in calcium because calcium is a key mineral needed to build strong bones. During childhood and adolescence, bones grow rapidly and reach their peak bone mass. Adequate calcium intake during these years helps ensure that bones become dense and strong, reducing the risk of fractures and conditions like osteoporosis later in life. Since bones are made up of layers of bone cells surrounded by calcium and other minerals, getting enough calcium supports healthy bone development.

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✔ Summary:

- Bones are hard due to calcium and minerals in bone tissue.
- Muscles are soft and flexible so they can contract and move.
- Both cell types are important for movement and body structure.
- Calcium is crucial for building strong bones, especially in growing children and teens.

This understanding helps explain why both bones and muscles work together — bones provide structure, and muscles provide motion!