Chlorophyll: Absorbing Light Energy for Photosynthesis

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  • 0:05 Photosynthesis Creates Food
  • 2:18 Pigments Absorb Light Energy
  • 3:11 Light Energizes Electrons
  • 4:00 Lesson Summary
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Lesson Transcript
Instructor: Kristin Klucevsek

Kristin has taught college Biology courses and has her doctorate in Biology.

Plants are clean, green, photosynthesizing machines. Using a specialized pigment called chlorophyll, plants are able to soak up energy from the sun and turn it into food. In this lesson, we'll start to learn why chlorophyll literally gets excited about a sunny day!

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.

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.

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