Sunlight provides energy to make food

Earlier, I compared a stem to a tall building.  Now I want you to think of a leaf as a sandwich.  A shiny, waxy layer cover the top “crust.”  It prevents water loss but still allows sunlight to enter.  A second slice of “bread,” the underside of the leaf, needs no such glossy protective “crust,” so it is paler and has no shine.  During daylight hours, this lower leaf surface opens thousands of holes, called stomata, to summer breezes.  Through these openings flow a constant supply of both oxygen and carbon dioxide. 

In our leaf “sandwich” between those two slices of bread, picture a filling of green kiwi jam loaded with tiny, dark green seeds.  These seeds, or chloroplasts, migrate through the jam and position themselves as close as possible to the sunlight, as its energy streams through the upper crust. 

Here, then, in this thin leaf sandwich are all the components of a tiny food factory.  A leaf’s food factory uses only three raw materials: water, oxygen, and carbon dioxide.  Roots supply an abundance of water. Oxygen and carbon dioxide enter the leaf through those holes in the underside of leaves.  Power to drive the leaf manufactory is not imported from electrical power plants or gas stations.  Rather a plant’s power arrives each day from sunrise to sunset, a constant, reliable, and free source of power called sunshine. 

On this bright day in mid-June, leaves have all they need to create their own food.  Dark-green-pigmented chloroplast absorb sunlight and convert it into tiny electrical charges.  A nearby water molecule (H₂O) absorbs a hit.  The molecule disintegrates into its components: two hydrogen atoms and one oxygen atom. Single atoms of oxygen and hydrogen are unstable and quickly seek new partners.  One oxygen atoms pairs with another to form a stable bond (O₂). The pair departs the scene through an open stomata and rejoins the weather in the garden.  Meanwhile, free hydrogen atoms, eager to create new bonds, seek partners among CO₂ molecules.  Atoms mate to produce more complex configurations, molecules we call glucose: C₆H₁₂O₆.

Thus, a tiny zap of electricity derived from sunlight has nudged atoms into new molecular combination to form glucose.  Glucose, also call sugar is THE basic building block of all food.  Plants store this sugar for future use as their own food.  We use the sugar in plant bodies as food for ourselves.

Can humans “make” food the same way plants can? No.  We can only harvest wheat berries, mill them into flour, and make bread.  Or we can feed corn, another grain, to chickens so they will grow up plump and juicy.  Or we can grow lettuces and herbs to add to a chicken salad.  But only plants can use sunlight in their own leafy factories to produce sugar.  In scientific terms, plants are “autotropic.”  That is, plants produce their own food and feed themselves.  No human can duplicate this process of photosynthesis.