I’ve Googled and every source I come across just says “plants gather (light) energy from the sun and use it for photosynthesis.” What exactly is “light energy”? Is is some sort of radiation? Is it just heat?
In: Planetary Science
Radiation in a spectrum that goes a bit beyond our ability to see, up into UV light. Heat is too low frequency for them to use in photosynthesis, but being comfortably warm helps with the chemical processes down the line.
The photons have to wiggle enthusiastically enough to be useful. They smash into chlorophyll and start a cascade of reactions that turns CO2 and water into sugar.
The process is complicated, but at it’s base it uses solar energy to separate water into oxygen and hydrogen ions. The reaction is actually electrochemical in nature, and electrons for this reaction are produced by light’s photons knocking them loose in chlorophyll molecules.
Technological analog would be having a photovoltaic cell used to electrolyze water.
Oxygen is released since plants have no use for it, but hydrogen ions are then reacted with carbon dioxide to make sugars and water, but that part of the reaction doesn’t need further energy input.
Plants have different types of cells, we colored lots of them in elementary school. Ever been sunburned? It’s the same energy but your cells don’t make oxygen when it happens
Every photon (particle of light) has energy. The amount of that energy depends on the light frequency. When absorbed by electrons in the atoms, this energy is converted into the energy level of the electron (it goes to higher orbitals). When photons (around the frequency of red) hit chlorophyl (the green pigment of plants), the electrons will jump from one chrolophyl to another, creating an “electron hole”. This “hole” will then “rip apart” a water molecule and create a high energy hydrogen ion, that can be used to synthetize organic compounds.
No, heat (a way of passing energy by random wiggling of molecules) is not enough to do photosynthesis.
Light energy is just photons, tiny particles of light, that plants turn into food during photosynthesis. It’s not heat or radiation, but a solar all-you-can-eat buffet for plants!
The mistake in your question is imagining that “light energy”, “radiation” and “heat” are different things in this question. The heat in question is infra-red radiation. The light energy is the same thing as visible light, which is also a type of radiation.
These are all the same thing, which is photons that are produced by the sun’s reactions, fly through space, enter the atmosphere, and smash into the plant, transferring some energy to it. The energy is used for chemical reactions.
The only difference between “light energy”, “heat” and other types of radiation is some properties of the photons that aren’t important for how the process works. The plant is better at absorbing some types of photons more than others and the sun emits more of some types of photons than others but that doesn’t really matter for the question.
This whole topic is called “electromagnetic radiation” if you want to learn more about it, and it covers visible light, infrared heat, radio waves, x-rays and microwaves.
NB. Saying that the radiation is “photons flying through space” is a simplification that I think is appropriate for ELI5. There are other ways to think about what is moving from the sun to the plant, but it’s enough for this question to say that the sun’s reactions produces some kind of products that travel to the plant and impart energy to it.
The energy from the sun reaches us as electromagnetic radiation in the form of photons. Photons can be visible light but also everything from radio waves to x-rays.
The part of the spectrum where the sun emits the most energy that reaches earth happens to be the part we decided to use for seeing.
Evolution has let us use the colors of light that the sun shines the brightest in to see.
Plants also mainly absorb photons (light) in the visible spectrum, because that is where the most energy is to be had.
To be more specific the absorb light that is blue (between 400 and 500 nm in wavelength) and red (around 600 to 700 nm).
There are different types of chlorophyll that do the absorbing with chlorophyll a more towards the edges of the spectrum and chlorophyll b more towards the center, but both lead a gap in the middle where the color green (495–570 nm) is, which is why leaves appear green, they reflect the part of the light they don’t use back at you.
Plants are like solar panels that run on sunlight, converting light energy into sugars through photosynthesis. It’s not exactly heat or radiation, but specific light waves.
How come plants don’t get sunburnt?
The cells have a molecule called chlorophyll inside a cell part called a chloroplast which can use the energy from absorbing light to assemble carbohydrates from carbon dioxide and water.
They appear green because they mostly absorb blue and red light which leaves green reflected to your eyes.
Latest Answers