Presentation on theme: "Chapter 6 PHOTOSYNTHESIS. A. Light Visible light makes up only a small portion of the electromagnetic spectrum. Sunlight consists of: ] 4% Ultraviolet."— Presentation transcript:
Chapter 6 PHOTOSYNTHESIS
A. Light Visible light makes up only a small portion of the electromagnetic spectrum. Sunlight consists of: ] 4% Ultraviolet (UV) radiation ] 44% Visible light ] 52% Infrared (IR) radiation
Characteristics of Visible Light: ] is a spectrum of colors ranging from violet to red ] consists of packets of energy called photons ] photons travel in waves, having a measurable wavelength ( ) = distance a photon travels during a complete vibration [measured in nanometers (nm)]
A photons energy is inversely related to its wavelength......the shorter the, the greater the energy it possesses. Which of the following photons possess the greatest amount of energy? Green photons = 530nm Red photons = 660nm Blue photons = 450nm
What happens to light when it strikes an object? ] reflected (bounces off) Only absorbed wavelengths of light function in photosynthesis. ] transmitted (passes through) ] absorbed
B. Photosynthetic Pigments Molecules that capture photon energy by absorbing certain wavelengths of light. 1. Primary pigments F Bacteriochlorophyll - green pigment found in certain bacteria. F Chlorophylls a & b - bluish green pigments found in plants, green algae & cyanobacteria.
Chlorophyll a is the dominant pigment in plant cells.
2. Accessory Pigments F Carotenoids - red, orange, yellow pigments found in plants, algae, bacteria & archaea. F Phycoerythrin - red pigment found in red algae. F Phycocyanin - blue pigment found in red algae & cyanobacteria. Each pigment absorbs a particular range of wavelengths.
C. Chloroplasts Sites of photosynthesis in plants & algae. Concentrated in mesophyll cells of most plants.
Chloroplast structure: ] Stroma - gelatinous matrix; contains ribosomes, DNA & various enzymes. ] Thylakoid - flattened membranous sac; embedded with photosynthetic pigments.
D. Photosynthesis Occurs in two stages: ] Light reactions - harvest photon energy to synthesize ATP & NADPH. ] Carbon reactions (Calvin cycle) - use energy from light reactions to reduce CO 2 to carbohydrate. 6CO H 2 O C 6 H 12 O 6 + 6O 2 + 6H 2 O
Overview of Photosynthesis
1. Light Reactions F require light F occur in thylakoids of chloroplasts F involve photosystems I & II (light harvesting systems). Photosystems contain antenna complex that captures photon energy & passes it to a reaction center.
Light Reactions of Photosynthesis
ATP Production by Chemiosmotic Phosphorylation
2. Carbon Reactions (Calvin cycle; C 3 cycle) F do NOT require light (occur in both darkness & light as long as ATP & NADPH are available) F occur in stroma of chloroplasts F require ATP & NADPH (from light reactions), and CO 2
Plants that use only the Calvin cycle to fix carbon are called C 3 plants. Ex. cereals, peanuts, tobacco, spinach, sugar beets, soybeans, most trees & lawn grasses.
E. Photorespiration Process that counters photosynthesis. Occurs when stomata close under hot, dry conditions: F O 2 levels in plant increase F CO 2 levels in plant decrease Under these conditions, rubisco fixes O 2 (rather than CO 2 ). Thus, PGAL is NOT produced.
F. C 4 and CAM Photosynthesis Adaptations that allow certain plants to conserve water and reduce photorespiration at higher temperatures. 1. C 4 Photosynthesis C 4 plants reduce photorespiration by physically separating the light reactions and Calvin cycle.
Leaf anatomy of a C 4 plant C 4 Photosynthesis: ] Light reactions occur in chloroplasts of mesophyll cells. ] Calvin cycle occurs in chloroplasts of bundle sheath cells.
2. CAM Photosynthesis CAM plants reduce photorespiration by acquiring CO 2 at night. Night: ] mesophyll cells fix CO 2 as malic acid ] malic acid is stored in vacuoles. Day: ] malic acid releases CO 2 which enters Calvin cycle. Malic acid