Detailed and comprehensive notes on chapter 10.3 of the Campbell biology textbook focuses on the light reaction from photosynthesis,it also cover the conversion of solar energy to the chemical energy of ATP and NADPH.
CONCEPT 10.3: The light reactions convert solar energy to the chemical energy of ATP
and NADPH
• Chloroplasts are solar-powered chemical factories
• Their thylakoids transform light energy into the chemical energy of ATP and NADPH
The Nature of Sunlight
• Light is electromagnetic energy, also called electromagnetic radiation
• Electromagnetic energy travels in rhythmic waves
• Wavelength is a measure of the distance between crests of electromagnetic waves
• It can range from less than a nanometer (gamma rays) to more than a kilometer (radio
waves)
• The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation
• Visible light (wavelengths 380 nm to 740 nm) drives photosynthesis and produces the
colors seen by the human eye
• Light also behaves as though it consists of discrete particles, called photons
• Each photon has a fixed quantity of energy which is inversely related to the wavelength
of light; shorter wavelengths have more energy per photon of light
Photosynthetic Pigments: The Light Receptors
• Pigments are substances that absorb visible light
• Different pigments absorb different wavelengths, and the wavelengths that are absorbed
disappear
• Wavelengths that are not absorbed are reflected or transmitted
– For example, most leaves appear green because chlorophyll absorbs violet-blue
and red light while reflecting and transmitting green light
–
• A spectrophotometer measures a pigment’s ability to absorb various wavelengths
, • It sends light through pigments and measures the fraction of light transmitted at each
wavelength
• An absorption spectrum is a graph plotting a pigment’s light absorption versus
wavelength
• Three types of pigments in chloroplasts include:
– Chlorophyll a, the key light-capturing pigment that participates directly in light
reactions
– Chlorophyll b, an accessory pigment
– Carotenoids, a separate group of accessory pigments
• The absorption spectrum of chlorophyll a indicates that violet-blue and red light will
work best for photosynthesis, while green is the least effective
• The action spectrum for photosynthesis, a profile of the relative effectiveness of
different wavelengths, confirms the effectiveness of violet-blue and red light
• The action spectrum of photosynthesis was first demonstrated in 1883 by Theodor W.
Engelmann
• He exposed different segments of a filamentous alga to different wavelengths of light and
used the growth of aerobic bacteria as a measure of O2 production
• The action spectrum for photosynthesis is broader than the absorption spectrum of
chlorophyll
• Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis
• The difference in the absorption spectrum between chlorophyll a and b is due to a slight
structural difference between the pigment molecules
• In the last decade, two other forms of chlorophyll were discovered—chlorophyll d and
chlorophyll f—that absorb higher wavelengths of light
• The cyanobacterium, Chroococcidiopsis thermalis, uses chlorophyll f in place of
chlorophyll a in shaded conditions
• Other accessory pigments called carotenoids, are yellow or orange because they absorb
violet and blue-green light
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller anyiamgeorge19. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $12.89. You're not tied to anything after your purchase.
