Membrane

"..."Huh, I never thought about it that way." I'm going to explain how organisms actually work - not dumbed down, but made clear. You'll learn about cell membranes, metabolic rates, growth plates, feedback loops, and ecosystem dynamics. All of it will be factual. None of it will require a biology degree to under..."

"...rst cell faced an immediate, existential problem: how to be separate from everything else while still interacting with it. The solution was the cell membrane. This might seem obvious now, but consider what it actually means. Before membranes, there were no "individuals" - just chemistry happening in soup...."

"...ing energy and converting ATP into ADP (adenosine diphosphate). That energy powers everything: muscle contractions, protein synthesis, nerve signals, membrane pumps, cell division. Then, the cell uses energy from food to reattach that third phosphate, converting ADP back into ATP."

"Why not just make cells bigger? Because cells have surface area problems. A cell needs to take in nutrients through its membrane (surface area) to feed its entire volume. As a cell grows, its volume increases as the cube of its radius (V = 4/3πr³), but its surface area only inc..."

"But it knows - with startling precision - whether it's swimming toward food or away from it. Every second, chemical receptors embedded in its membrane sample the environment. Rising glucose? Keep swimming straight. Falling glucose? Tumble, pick a new direction, try again. This single-celled organis..."