A Sugary Solution

"If plants use photosynthesis to make sugar for energy and growth, why don't plants taste like sugar?" - Anon.

How amazing would it be to make sugars anytime you wanted just by standing out into the sun and taking a deep breath... This is all plants do. They don't need three solid meals a day. They get all their energy just by converting the sugars they make during photosynthesis into ATP. But that's not all plants use their produced sugar for. Some sugar goes to fruits to aid reproduction. Others are used to help build the plant bigger and taller.

So that takes us to the question at hand. If plants use sugar to grow, why don't leaves taste like sugar? To answer that, we should start by looking at sugar itself. Sugar comes in a variety of styles, determined mostly by how big the molecule is. The simplest, smallest form of sugar is glucose (C6H12O6). This is the sugar that is used to make energy in our cells. But there are other types of sugars too! Fructose and galactose are also simple sugars. These sugars are called monosaccharides because there are only one of them. If more than one of these is joined together, you can get disaccharides or polysaccharides (same thing as carbohydrates).

Who knew sugar was so complicated?!

When we eat fruit, we are often are eating fructose. Some fruits (like mangoes) also have pectin (which is what makes it sour), which is a polysaccharide. The great thing about plants is that they treat sugars like legos. Photosynthesis will provide them the building blocks they need to make whatever they want. If they are in the reproduction phase of their life, they will turn it into fructose for fruit. If they are hungry, they will use glucose for energy. If they are ready to build new cells for growth, they will make cellulose. It's all just a combination of 6 carbons, 12 hydrogens and 6 oxygens in repeating units.

It's kind of like candy crush, just a puzzle made of sugars.

If you think about eating plants, you can really see this in action. Some parts of plants are sweet and tasty (grape = fructose), others are sour (lime = pectin), and others still are bitter and not sweet at all (broccoli = cellulose). But they all come from the same thing, putting together sugars. Another example is bread, which is a polysaccharide (carbohydrates). It doesn't taste sweet, but it just a bundle of glucose molecules that our body turns into energy.

Interestingly enough, some polysaccharides can be digested (starches), while others cannot (fibers). They are both very important for our body, but the key difference is that fibers pass straight through us, providing no energy. This is because our bodies don't have the necessary tools to break down fibers like cellulose, inulins and pectins. However, other animals like cows, do have these tools. This is why you will find cows eating grass. Their stomachs can break down any polysaccharides, meaning 100% of the plant will give them energy. If you sit outside all day eating nothing but grass, you will still starve to death.

Grass, grass everywhere and not a blade to eat...