A direct answer: Without a plasma membrane, cells would be unable to maintain homeostasis, regulate the internal environment, and control the passage of substances. This would disrupt essential processes and typically lead to loss of ion balance, nutrient depletion, buildup of toxic compounds, and failure of critical cellular activities. Context and key points

• Homeostasis and selective permeability: The plasma membrane acts as a selective barrier that regulates which ions and molecules can enter or leave the cell, helping to maintain stable internal conditions. Without this control, intracellular concentrations would drift away from optimal levels, interfering with metabolism and signaling.
• Nutrient uptake and waste removal: The membrane enables controlled transport of nutrients into the cell and export of waste products. In its absence, the cell could not efficiently acquire necessary nutrients or remove toxic byproducts, compromising viability.
• Signaling and cooperation: Membrane proteins function as receptors and channels crucial for communication, environmental sensing, and coordinating responses with other cells. Losing these functions would impair growth, development, and tissue organization.
• Structural integrity and protection: The membrane provides structural support and protects against mechanical stress and harmful substances. Without it, the cell would be far more vulnerable to damage.
• Consequences at higher organization levels: In multicellular organisms, disrupted membrane function in individual cells can cascade to tissues and organs, undermining organism-wide homeostasis and health.

If you’d like, I can tailor this to a particular organism (bacteria, plant, or animal cells) or explain how specific transport processes (like osmosis, diffusion, and active transport) depend on the membrane.