Chlorophyll: Absorbing Light Energy for Photosynthesis
Light Energizes Electrons
Chlorophyll contains electrons that are normally at a low energy state, or ground state. But when chlorophyll absorbs light energy, the electrons get really excited. Literally! They jump to a high energy level, or excited state. Although we'll save the details of this process for other lessons, this super-excited electron is then transferred from the chlorophyll pigment to a primary electron acceptor. Hence, chlorophyll becomes oxidized. Photosynthesis can use both chlorophyll pigments and other accessory pigments that reflect colors other than green. These accessory pigments aren't exactly the jewelry-type accessories of photosynthesis, but they are as helpful as the right pair of shoes to complete an outfit. These accessory pigments absorb other wavelengths of light and pass on energy to chlorophyll, expanding the range of wavelengths that can be used for photosynthesis.
Photosynthesis Creates Food
If you've looked outside today, or even around your house, you've likely seen a plant. Trees, potted plants, ferns, grass, weeds, flowers, maybe (if you're lucky) some palm trees - there is plenty of plant diversity on the planet that we often don't take enough time to appreciate on a daily basis. It's also likely you haven't taken a minute to thank a plant today for something vital it's giving to you right this second. While the rest of us need to eat to get energy, plants have the awesome ability to make their own food simply by soaking up some sunshine and taking a drink of water. That is pretty amazing, if you think about it. Plants, as well as some bacteria and protists, perform photosynthesis, or a process that converts energy from sunlight into food. No eating is required to get the energy they need for the day - just a healthy dose of sunlight, carbon dioxide and water! The chemical equation for photosynthesis is 6CO2 (or carbon dioxide) + 6H2O (or water) yields C6H12O6 (which is glucose) + 6O2 (or oxygen). Chemical equation for photosynthesis Chemical Equation for Photosynthesis If you've already learned about cellular respiration, or the process that converts food into chemical energy, then this formula should look pretty familiar to you. In fact, photosynthesis is essentially the reverse of cellular respiration. Photosynthesis uses the carbon dioxide you breathe out, along with sunshine and water, to create sugars and expel oxygen - because, as we all know, you and I both appreciate using that sugar and oxygen to perform cellular respiration. It's what keeps us alive. So, here it is folks: this is the circle of life. So, have you thanked a plant today for the fresh air you breathe in? Processes of cellular respiration and photosynthesis Cellular Respiration Process In this lesson, we'll start to investigate one of the major players in this process that is contained within plant chloroplasts, or organelles that are the site of photosynthesis. Chloroplasts reside in most leaf cells. Both chloroplasts and the leaves themselves are different shades of green due to a lovely pigment they contain. A pigment is a compound that absorbs a particular wavelength of visible light. Chlorophyll is a green pigment contained in thylakoid membranes of chloroplasts that is used in photosynthesis by plants. In bacteria that also perform photosynthesis, chlorophylls are in the plasma membrane.
Summary
In summary, photosynthesis is the process that converts energy from sunlight into food in plants and some protists and bacteria. Photosynthesis is essentially the reverse of cellular respiration, where our bodies convert food into usable energy. Photosynthesis is driven by the use of a pigment or molecule that absorbs a specific wavelength of energy. In this case, the primary pigment is chlorophyll, which is a pigment that absorbs blue and red wavelengths while reflecting green wavelengths. Chlorophyll exists within the thylakoid membranes of plant chloroplasts, and that's what makes plants green! In photosynthesis, sunlight energizes electrons in chlorophyll, moving them to a higher energy state. In turn, chlorophyll molecules become oxidized, and these electrons are used in the next steps of photosynthesis.
Pigments Absorb Light Energy
So you might be wondering, how does a pigment absorb light to fuel photosynthesis? First, we need to talk about light itself. The electromagnetic spectrum is the range of wavelengths from the radio waves of your car stereo to high-energy gamma rays. Chlorophyll and other pigments absorb specific visible wavelengths of the electromagnetic spectrum. The visible light is literally the colored wavelengths that are visible to your eyes. They range from red, at a wavelength of 700 nm, to blue, at a wavelength of 400 nm. Shorter wavelengths have higher energy (such as blue), and longer wavelengths (like red) have lower energy. Chlorophyll mostly absorbs blue and red wavelengths from sunlight. Therefore, it reflects the middle part of this visible spectrum, the green wavelengths. Illustration of the visible light spectrum and the full electromagnetic spectrum Light Spectrum This is why plants look green to us. The color of a pigment is the wavelength of light that is reflected, or the wavelength that is not absorbed.
