The correct option is (c).
Explanation
The plasma membrane, also known as the cell membrane, is a biological barrier that separates the interior of a cell from its external environment. It is a vital structure present in all cells that defines their boundaries and regulates interaction with the surroundings.
Statement 1 is Incorrect:
While the plasma membrane is the outermost covering in animal cells, it is not the outermost layer in all organisms. In plant cells, fungi, and bacteria, there is a rigid protective layer called the cell wall located exterior to the plasma membrane.
Statement 2 is Correct:
The plasma membrane is selectively permeable. It regulates the movement of substances, allowing essential materials (such as oxygen, water, and nutrients) to enter and waste products (such as carbon dioxide) to exit, while preventing the passage of harmful or unnecessary substances.
Statement 3 is Correct:
The plasma membrane is a flexible structure primarily composed of organic molecules: lipids (specifically a phospholipid bilayer) and proteins. This flexibility is crucial for various cellular processes, such as cell growth and endocytosis (the ingestion of food and other materials from the external environment).
Key Takeaway:
The plasma membrane is a selectively permeable boundary made of lipids and proteins found in all cells. However, in plants, fungi, and bacteria, it is surrounded by an external cell wall.