Dr. Gideon Lapidoth
Enzymes and Climate Change
Current projections have the world population reaching nearly 10 billion by 2050, accordingly, doubling the required food supply from current levels. Presently, food production is just not keeping pace with population growth. We are already ‘in the red’ with nearly ½ a billion people chronically undernourished, and an estimated 25K people are dying from hunger every day worldwide.
Paraphrasing Archimedes, who once said: “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world,” I would say: “Give me enough energy, and we will feed every man, woman, and child on earth.” You might be skeptical and say humans can’t consume electricity, heat, or any other forms of abstract energy; we consume carbohydrates, proteins, and fats, actual matter. So to feed more people, we need more raw material, right? And raw material is a finite resource, and by simple logic, we will eventually run out of it. Well, let’s think about that for a second; why do we consume food?
1. Nutrients - The chemical compounds that our bodies use to build our cells. Almost 99% of the human body mass is made up of six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Some simple math would show that the planet has all the material we need to ‘build’ the entire human population multiple times over. For example, our bodies’ second most abundant element is carbon (this is the number 1 element in our bodies discounting the water mass, which counts for about 60%, see Fig. 1). Carbon accounts for ~18% of our total body mass. An average body weighs 70Kg. Multiply that by the current world population of roughly 8 billion (give or take a few hundred million) that comes out to about 122 million tons. For comparison, there are about 1.85 billion, billion(1018) tons of carbon on our planet. We can repeat the math for the other elements, but for brevity, I’ll jump to the main conclusion: There is no shortage of ‘raw material’ to sustain the human population on the planet, not even close.
Fig. 1 Breakdown of the main elements that make up the human body
So let's discuss the other reason we consume food:
2. Energy - The recommended minimum amount of calories per adult is 2,500, which is equivalent to about 2 pounds (1 kg) of sugar. Most of the food mass we consume daily is for energy requirements.
But what does that exactly mean? What does it mean when we say we are getting energy from food.
Fuel in our bodies works almost precisely like fuel in our cars. We oxidize carbohydrates, breaking up chemical bonds to release energy that is stored in those chemical bonds. If we work our way up (or down, depending on how you look at it), the food chain, the source for that energy is the sun.
Fig. 2 Oxidizing sugar works exactly like burning gas in our cars. The reaction releases energy. Note that no material vanishes in the process; only chemical bonds are broken.
Our planet absorbs from the sun about 102 quintillion (that’s 1018) calories in the form of solar radiation every hour(!). That’s enough energy to feed every man, woman, and child on the planet for 11,000 years. The problem is that we cannot utilize this energy directly. We have first to convert it into chemical energy, namely sugar. This is the vital role plants play in this process. Plants have the mechanism to extract energy from sunlight and use it to build chemical bonds.
The ‘secret sauce’ that allows plants to achieve this is a specific array of enzymes named “Photosystem I” and “Photosystem II.” These enzymes perform the chemical magic that essentially stores the sun’s energy in chemical bonds. Now, here are a few numbers that I want you to think about. First, we do not consume the entire mass of agricultural plants, only an edible portion. This ratio between edible biomass (usually in the form of grains) and the above-ground nonedible mass (e.g., stalk, leaves, husks, tassels, etc.) is known as the “harvest index” and is roughly 50%, meaning for every 1 pound of harvested biomass only about 0.5 pounds is edible. The rest is either burned or used as animal feedstock. Second, plants are not that efficient at converting light energy into chemical energy. Wheat, for example, converts about 240 million calories (1 terajoule) of sunlight energy to 1.2t biomass (or 0.6t of edible biomass). 240 million calories are converted to only 2,040,000 calories. That’s less than 1% of sunlight into edible calories, underwhelming, to say the least. For comparison, silicon solar panels have an operational efficiency of 20%.
Let’s look at this in another way, 1 hectare of farmland produces between 5-10 tons of grain per year, that’s about 40,000,000 calories. That’s the same amount of solar energy that hits a hectare of land in just under two days(!). On top of that, plants don’t just need sunlight; they need another vital resource - water. One kg of wheat grain requires about 1300 liters of water.
But why so much? It takes 6 molecules of carbon dioxide and 6 molecules of water (H2O) to produce 1 molecule of sugar (glucose). By mass, 1 kg of sugar would require only 0.8 liters of water, so where did the rest of the 1299.2 liters go? As it turns out, plants require large amounts of water for other functions, principally respiration.
Can we do anything about that? Well, quite a lot. Humans have relied for several millennia on what nature provides, which admittedly is quite a lot, but nature was not optimized to provide humanity’s needs; it was optimized to do what all living beings do, survive and multiply. From an engineering perspective, plants have many redundant systems that siphon energy and other resources from humanity’s main objective: edible calorie production. Who says we need to use plants at all? Just as we replaced horses with more efficient modes of transportation, we can build highly efficient molecular engines that convert energy into chemical bonds. We have the technology to design and build enzymes that can directly use electrical or heat energy to build chemical bonds.
This is one of the global challenges that Enzymit seeks to solve. We are currently designing a set of enzymes that can use the chemical energy stored within phosphate salts to drive chemical reactions such as condensation of carbon dioxide to form complex carbohydrates, essentially photosynthesis but with much greater efficiency, no sun, nutrients, and excess water required. What’s exciting is that this is just the tip of the iceberg.
Nothing is out of reach; all it requires from us is to reevaluate what is possible.