Biolog 7 - Chapter 7: Photosynthesis A. Energy Source The...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 7: Photosynthesis A. Energy Source The leaves are the major site of photosynthesis for most plants. The color of a leaf comes from chlorophyll, the green pigment in the chloroplasts. Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of the leaf. O 2 exits and CO 2 enters the leaf through microscopic pores called stomata in the leaf. Each chloroplast has two membranes around a central aqueous space, the stroma. In the stroma is an elaborate system of thylakoids. a) Thylakoids may be stacked into columns called grana . b) Chlorophyll is located in the thylakoids. B. Photosynthesis Reactions In the thylakoid membrane, chlorophyll is organized along with proteins and smaller organic molecules into photosystems. Each light-harvesting complex consists of pigment molecules (which may include chlorophyll a , chlorophyll b , and carotenoid molecules) bound to particular proteins. When any pigment molecule absorbs a photon, it is transmitted from molecule to molecule until it reaches a particular chlorophyll a molecule, the reaction center. At the reaction center is a primary electron acceptor, which accepts an excited electron from the reaction center chlorophyll a . Photosystem I (PS I) has a reaction center chlorophyll a that has an absorption peak at 700 nm. Photosystem II (PS II) has a reaction center chlorophyll a that has an absorption peak at 680 nm. These two photosystems work together to use light energy to generate ATP and NADPH. C. Light Dependent Reactions In the light reactions, light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to NADP + forming NADPH. NADPH, an electron acceptor, provides reducing power via energized electrons to the Calvin cycle. Water is split in the process, and O 2 is released as a by-product. Generates ATP using chemiosmosis in a process called photophosphorylation . Thus light energy is initially converted to chemical energy in the form of two compounds: NADPH and ATP. D. The Calvin cycle (or light-independent reactions) Begins with the incorporation of CO 2 into organic molecules, a process known as carbon fixation. The fixed carbon is reduced with electrons provided by NADPH. ATP from the light reactions also powers parts of the Calvin cycle. Calvin cycle makes sugar with ATP and NADPH from the light reactions.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Calvin cycle occurs in the stroma. The light reactions convert solar energy to the chemical energy of ATP and NADPH. While light travels as a wave, many of its properties are those of a discrete particle, the photon. Photons are not tangible objects, but they do have fixed quantities of energy. The amount of energy packaged in a photon is inversely related to its wavelength. Photons with shorter wavelengths pack more energy. Different pigments absorb photons of different wavelengths, and the wavelengths
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 12/03/2011 for the course CHEM BIO P 101 taught by Professor Kk during the Spring '11 term at Rochester.

Page1 / 5

Biolog 7 - Chapter 7: Photosynthesis A. Energy Source The...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online