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Living cells are constantly exposed to various signals from their surroundings. These signals can be: Chemical: Such as hormones, pathogen signals, mating signals, and ozone. Physical: Such as changes in light, temperature, and pressure. To respond appropriately to these signals, cells have special proteins called receptors on their surface. These receptors detect the signals and convert them into internal messages that the cell can understand and act upon. How Signals are Processed? 1. Signal Detection: receptors on the cell surface. 2. Transduction: • The receptor activates proteins inside the cell, which then produce molecules called "second messengers." 3. Signal Amplification and Cascades: These second messengers amplify the signal and pass it on to other proteins, triggering a cascade of reactions. 4. Response: • The cascades can lead to changes in gene expression, enzyme activity, or cell behavior, ultimately leading to a physiological response. What are Phospholipids? Structure: Phospholipids are a type of lipid molecule that are a major component of all cell membranes. They consist of two fatty acid tails that are hydrophobic (repel water) and a phosphate head that is hydrophilic (attracts water). This unique structure allows them to form bilayers, creating the fundamental structure of cell membranes. Where are Phospholipids Found in Plants? Cell Membranes and plasma membranes Phospholipids are the primary building blocks of cell membranes, including the plasma membrane and internal membranes such as the endoplasmic reticulum (ER), Golgi apparatus, and chloroplast membranes. Read less