H G Which organelle is labeled H?
The Correct Answer and Explanation is:
Correct Answer: Cell Membrane
The organelle labeled H is the cell membrane, also known as the plasma membrane. This essential structure forms the outer boundary of the animal cell, separating the internal cellular environment, or cytoplasm, from the external surroundings. In the provided diagram, the line for H clearly points to this thin, flexible layer that encloses all other organelles.
The cell membrane’s primary function is to be selectively permeable. This means it meticulously controls which substances, such as nutrients, ions, and waste products, can enter and exit the cell. This regulation is crucial for maintaining a stable internal environment, a state known as homeostasis, which is necessary for cellular activities.
Structurally, the cell membrane is described by the fluid mosaic model. It is primarily composed of a double layer of phospholipids, called a phospholipid bilayer. Each phospholipid molecule has a hydrophilic (water loving) head that faces the watery environments inside and outside the cell, and two hydrophobic (water fearing) tails that face inward, away from the water. This arrangement creates a stable yet flexible barrier.
Embedded within or attached to this bilayer are various types of proteins. These proteins perform a wide range of functions. Some act as channels or pumps to transport specific molecules across the membrane. Others function as receptors that bind to signaling molecules like hormones, allowing the cell to respond to its environment. Some proteins act as anchors, connecting the membrane to the internal cytoskeleton or the external extracellular matrix, providing structural support. Carbohydrate chains are often attached to proteins and lipids on the outer surface, forming the glycocalyx, which is important for cell recognition and adhesion. Unlike plant cells, animal cells do not have a rigid cell wall, making the cell membrane their definitive outer limit.
