Final answer:
The plasma membrane is composed of a phospholipid bilayer with embedded proteins and cholesterol, separating the cytoplasm from the extracellular environment. Inside the membrane is the cytoplasm with ribosomes, while outside is the extracellular fluid. It functions to protect the cell and regulate the passage of substances.
Step-by-step explanation:
The plasma membrane is a critical component of an animal cell that provides a barrier between the cell's cytoplasm and the environment outside the cell. The membrane's structure is composed mainly of a phospholipid bilayer, with the hydrophobic tails facing inward and the hydrophilic heads facing outward. Embedded within this bilayer are various proteins that perform functions such as transport and cell communication. Additionally, cholesterol molecules are present which contribute to the fluidity and stability of the membrane.
Directly inside the plasma membrane is the cytoplasm, which includes a watery substance called cytosol and cell structures such as ribosomes where protein synthesis occurs. The nucleus, which houses DNA and is essential for genetic instruction and control, is also encased within the cell and surrounded by the cytoplasm. Directly outside the plasma membrane, one would find the extracellular fluid, which contains nutrients, hormones, and waste products pertinent to the cell's function and interaction with other cells.
The plasma membrane serves not only as a physical barrier but also regulates the entry and exit of substances, thus maintaining homeostasis within the cell. The membrane's selective permeability allows it to control substances moving in and out, ensuring that essential nutrients enter while waste products are expelled.