Photosynthesis : Photosynthesis BIOLOGY Light : Light Behaves as if it has both
Wave motion—the distance between the crests of two waves is called the wavelength. Visible Light : Visible Light Has wavelength of 380-750 nm
The shorter the wavelength, the more energy.
Light can excite atoms and move electrons to higher energy levels. Then either:
energy is dissipated as heat
energy is given off as light (fluorescence)
The electron may be lost from the atom and may be accepted by NADP+ in photosynthesis NADP+ Photosynthetic Pigments : Photosynthetic Pigments Most pigments absorb some wavelengths of light and reflect or transmit other wavelengths.
The color seen is that which is reflected.
Chlorophyll a is the main photosynthetic pigment.
Has a porphyrin ring
(similar to hemoglobin)
with a central atom of Mg Photosynthetic Pigments : Photosynthetic Pigments Chlorophyll b—yellow-green, C55H70O6N4Mg
Chlorophyll a and b absorb energy from blue, violet, and red.
Accessory pigments—can absorb energy from other regions of the spectrum. Include
Carotenoids—orange, dark yellow
Anthocyanins--reds Photosynthetic Organisms : Photosynthetic Organisms Photosynthesis transforms solar energy into the chemical energy of a carbohydrate.
Heterotrophic organisms use organic molecules produced by photosynthesizers as a source of chemical energy. Flowering Plants : Flowering Plants CO2 enters leaf through stomates.
CO2 and water diffuse into chloroplasts.
Double membrane surrounds fluid (stroma).
Inner membrane system within stroma form flattened sacs (thylakoids).
Often stacked to form grana (singular granum).
Chlorophyll and other pigments within thylakoid membranes are capable of absorbing solar energy. Figure 36.12x Stomata on the underside of a leaf : Figure 36.12x Stomata on the underside of a leaf Figure 10.9 Location and structure of chlorophyll molecules in plants : Figure 10.9 Location and structure of chlorophyll molecules in plants How do we know chlorophyll is absorbing light? : How do we know chlorophyll is absorbing light? Photosynthetic Reactions : Photosynthetic Reactions Light Reaction - Chlorophyll absorbs solar energy and energizes electrons.
Electrons move down electron transport chain.
Solar energy ATP, NADPH
Noncyclic electron pathway
Cyclic electron pathway
Calvin Cycle Reaction - CO2 is taken up and reduced to a carbohydrate.
Reduction requires ATP and NADPH.
ATP, NADPH Carbohydrate Noncyclic Electron Pathway : Noncyclic Electron Pathway Electron flow can be traced from water to a molecule of NADPH.
Uses two photosystems, PS I and PS II.
One Photosystem consists of a pigment complex and electron acceptor molecules in the thylakoid membrane. Cyclic Electron Pathway : Cyclic Electron Pathway Cyclic pathway begins when PS I pigment complex absorbs solar energy and is passed from one pigment to another until it is concentrated in a reaction center.
Pathway only results in ATP production. Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts : Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts Figure 10.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane : Figure 10.16 The light reactions and chemiosmosis: the organization of the thylakoid membrane Calvin Cycle Reactions : Calvin Cycle Reactions Calvin cycle is a series of reactions that produce carbohydrates before returning to the starting point again.
Utilizes atmospheric carbon dioxide to produce carbohydrates. Includes:
Carbon dioxide fixation
Carbon dioxide reduction
RuBP Regeneration Calvin Cycle Reactions : Calvin Cycle Reactions Carbon Dioxide Fixation
CO2 is attached to RuBP, a 5-carbon molecule. The result is a 6-carbon molecule which splits into two 3-carbon molecules.
The enzyme, Rubisco, speeds up this reaction. Importance of Calvin Cycle : Importance of Calvin Cycle PGAL (glyceraldehyde-3-phosphate) is the product of the Calvin cycle that can be converted to a variety of organic molecules.
A plant can use the hydrocarbon skeleton of PGAL to form fatty acids and glycerol, which are combined in plant oils. Photosynthesis Overview : Photosynthesis Overview C4 Photosynthesis : C4 Photosynthesis In C4 leaf, mesophyll cells are arranged around the bundle sheath cells.
CO2 and PEP form oxaloacetic acid (4 C) in the mesophyll cells. When needed, CO2 is released to the bundle sheath cells for the Calvin cycle.
In hot, dry climates, photosynthetic rate of C4 plants is about 2-3 times that of C3 plants.
Avoids photorespiration: fixed carbon in a plant is returned to CO2 (as much as 50% in C3 plants returns to CO2) Examples of C4 Plants : Examples of C4 Plants Corn
Millet CAM Photosynthesis : CAM Photosynthesis Crassulacean-Acid Metabolism
C4 plants partition carbon fixation in space, while CAM partitions by time.
At night, CAM plants fix CO2, into C4 molecules in large vacuoles.
C4 molecules release CO2 to Calvin cycle when NADPH and ATP are available.
Water Conservation—CAM plants use 18-25 g H2O per g of dry plant (C3 plants use 500-1200 g and C4 plants 250-450 g.) Examples of CAM Plants Cactus
Aloe vera Figure 10.19 C4 and CAM photosynthesis compared : Figure 10.19 C4 and CAM photosynthesis compared Factors That Affect the Rate of Photosynthesis : Factors That Affect the Rate of Photosynthesis Temperature—increasing temperature increases the rate up to 35 degrees Celsius, then decreases rapidly (enzyme denaturation)
Light intensity—rate increases up to about 1/3 of the intensity of summer sunlight then declines because stomates close to cut water loss
Wavelength of light—red, blue and violet are absorbed most of chlorophylls a & b.
CO2 level—up to a certain point increasing the CO2 level increases the rate of photosynthesis
Water—a shortage of water decreases the rate because it is a raw material.
Minerals—Mg and N are need for chlorophyll formation; Zn, Mn, Fe, and Cu are needed for metabolic reactions