The correct answer is A. Cell membrane.
A cell membrane is a semi-permeable membrane that separates the cell from its environment. It is made up of a phospholipid bilayer, which is a double layer of phospholipid molecules. The phospholipid molecules have a hydrophilic head and a hydrophobic tail. The hydrophilic heads are attracted to water, while the hydrophobic tails are repelled by water. This arrangement of phospholipid molecules creates a barrier that allows some molecules to pass through while others cannot.
Water, oxygen, and carbon dioxide can pass through the cell membrane freely. However, larger molecules, such as proteins and carbohydrates, cannot pass through the cell membrane without the help of a transport protein. Transport proteins are embedded in the cell membrane and allow specific molecules to pass through the membrane.
The cell membrane is a vital part of the cell. It protects the cell from its environment and allows the cell to take in nutrients and expel waste products.
The other options are incorrect because they are not semi-permeable membranes.
- Option B, plasma membrane, is another name for the cell membrane.
- Option C, cell wall, is a rigid structure that surrounds the cell membrane in plant cells. It provides support and protection for the cell.
- Option D, nucleus, is the control center of the cell. It contains the cell’s DNA, which is the blueprint for the cell’s structure and function.