If cell membranes are made up of lipids (fats), why do foods like lettuce have so few calories even though there are a lot of cells in it?
In: Biology
Plant cells have rigid cellulose walls that are largely indigestible to humans. What little nutritional value they do have is often inaccessible.
More generally, cell membranes are very thin comparatively. Think of a big bucket filled with water balloons. They fill the bucket, but there’s hardly any balloon rubber in there.
Mostly because plant cells are usually much bigger and more full of water than animal cells. What this means is that for an equal weight of lettuce or meat, the lettuce has far fewer cell membranes and so less fats. Another reason is that fats in animal cells are important to keep the membranes fluid, etc, while plant cell membranes are much thinner due to the fact that they also have a rigid cell wall. This wall is made of cellulose, which we can’t digest, and so has very little caloric value.
A simple experiment (which I’m sure you’ve already done) is to cook some spinach – in no time it goes from a whole lot to almost nothing because it’s is pretty much mostly water and that water escapes once the cells begin to rupture from heat.
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