Question

problem b: calcium (ca²⁺) is needed in our bones to rebuild them and keep them strong. calcium is used up by the bone cells and needs to be replaced. because calcium is an ion, meaning it has a charge (+), it will be rejected by the hydrophobic region of the cell membrane and cannot pass directly through. how can bone cells get enough calcium to maintain their strength? energy required?

Explanation:

Calcium ions ($Ca^{2+}$) cannot pass directly through the cell - membrane's hydrophobic region. Active transport is a process that uses energy to move substances against their concentration gradient. Carrier proteins in the cell membrane can bind to calcium ions and use energy (such as ATP) to transport them into the bone cells. This allows bone cells to obtain the necessary calcium for maintaining strength.

Answer:

Bone cells obtain enough calcium through active transport. Carrier proteins in the cell membrane use energy (usually ATP) to move calcium ions ($Ca^{2+}$) against their concentration gradient into the cells, as calcium cannot pass directly through the hydrophobic region of the cell membrane.