Biology — Introduction to Cells and Cell Theory + 7 more topics

Cells are the smallest units of life that can perform all the functions necessary for life, such as metabolism, growth, and reproduction. They're incredibly diverse, but all share some basic components.

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The plasma membrane is a sophisticated structure that protects the cell and mediates its interactions with the outside world. It's not a rigid wall but a flexible, constantly moving barrier.

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• Rough ER (RER): Covered in ribosomes, giving it a "rough" appearance. Its primary job is to synthesize proteins destined for secretion, insertion into membranes, or delivery to other organelles (like lysosomes or the Golgi). As ribosomes build these proteins, they enter the RER lumen (the space inside the ER) for folding and modification.
• Smooth ER (SER): Lacks ribosomes. It's involved in synthesizing lipids (like phospholipids and steroids), detoxifying drugs and poisons (especially in liver cells), and storing calcium ions (important for muscle contraction).

Life is built in a hierarchy, starting small and getting more complex. Each level builds upon the last, leading to a fully functional organism.

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