In eukaryotic plants and algae photosynthetic pigments occur in thylakoid membranes arranged as grana stacks in the chloroplasts The main photosynthetic pigments are chlorophyll a chlorophyll b carotene and xanthophyll 6 CO2 H2O 686 kilocalories C6H12O6 6 O2 Photosynthesis relies on two main stages not in Biology Lab Practical 2 Notes Chapter 7 Photosynthesis o o The photochemical or light reactions are solar powered The biochemical reactions of the Calvin cycle do require light Photochemical reactions split water energize electrons photosynthetic pigment molecules and release oxygen molecules Biochemical reactions use the energy generated by the photochemical reactions to fix carbon into sugars Photochemical or Light Biochemical Reactions Reactions Light dependent Instantaneous Captures energy activated electron transport chain Calvin Cycle Light not required Fast but not nearly instantaneous Uses energy glucose Splits water to release O2 Fixes carbon dioxide to Photochemical Reactions A The Effect of Light Intensity Thylakoid membranes inside plant chloroplasts house chlorophyll pigments organized into two photosystems A photosystem is an enzymatic protein complex that uses light to reduce molecules and power the electron transport chain The two photosystems are identified by their optimum wavelength Photosystem 1 has an optimum wavelength of 700 nanometers and photosystem II has an optimum wavelength of 680 nm The photosystems are named for their order of discovery and not for the sequence of electron flow They operate at almost 100 efficiency Solar energy absorbed by photosystem II excites electrons in the chlorophyll to a higher energy level These high energy electrons are trapped by primary electron acceptors and are replaced by electrons extracted from water releasing oxygen as a by product Electrons from photosystem II pass down the electron transport chain yielding energy to generate ATP Light energy is also absorbed by photosystem I where it excites the chlorophyll causing electrons to pass to another terminal acceptor molecule Unlike photosystem II which replaces its chlorophyll electron deficit by splitting water molecules the chlorophyll electron deficit of photosystem I is filled by electrons passed down the electron transport chain from photosystem II Electrons from Photosystem I s terminal electron acceptor enter a second ETC where they reduce NADP to NADPH which is required for the biochemical reactions of the Calvin Cycle It is possible to measure the effect of light intensity on electron transport by substituting NADPH with DPIP In its oxidized state DPIP is blue after it accepts electrons DPIPH2 is chemically reduced and becomes clear The Effect of Light Wavelength We see color because objects contain pigments that selectively absorb some wavelengths of visible light and reflect or transmit others An action spectrum charts the effectiveness of different wavelengths of light on photosynthesis The faster the rate of photosynthesis the quicker the leaf disks float The Activity of Photosynthetic Pigments Photosynthetic pigments determine which wavelengths of light are used for photosynthesis In photosynthetic eukaryotes chlorophyll and chlorophyll are the main pigments although other such as carotene and xanthophyll may be present Chlorophylls are large ring molecules with nonpolar hydrocarbon tails Carotenes and xanthophyll s are nonpolar hydrocarbon chains In all cases the nonpolar hydrocarbon portion of the molecules anchors the pigments to the thylakoid membranes within chloroplasts Rf distance moved by pigment distance from origin to solvent front Although the action spectrum tells you what wavelengths of light are important for photosynthesis it tells you nothing about the pigments responsible for photosynthesis at specific wavelengths Each photosynthetic pigment has a unique light absorption signature which can be plotted as an absorption spectrum Action and absorption spectrum are high at violet and red Biochemical Reactions The light independent reactions of the Calvin cycle convert or fix atmospheric carbon dioxide to sugars that can be stored in the plant body When present anthocyanin pigments are found in the vacuoles of leaf cells Cunn found anthocyanin s were most abundant in older leaves on understory trees where gaps in the forest canopy exposed leaves sun beams His hypothesis was anthocyanins may protect shade adapted chloroplasts from short exposures to high intensity sun Bioengineered Carbon Fixation It requires more energy to produce biofuels than is obtained and process is NOT carbon neutral The greater the light intensity the lower the absorbance will be Chapter 8 Cell Division A foundation principle of biology is cells are derived from other cells Genetic information passes to a new generation when a cell divides to form daughter cells Cell division is the basis for growth and repair of multicellular organisms The cell division begins with DNA replication followed by DNA separation cytoplasmic division and separation into daughter cells Prokaryotic Cell Division The simplest form of cell division is binary fission in prokaryotic cells Binary fission begins with replication of the circular DNA strand The replicated DNA strand attaches to the plasma membrane and separates as the cell elongates The division of the cytoplasm is called cytokinesis Bacterial DNA has a high mutation rate Populations that reproduce by binary fission increase exponentially Asexual Reproduction in Eukaryotes Eukaryotic DNA is arranged in linear chromosomes which are housed in a membrane bound nucleus to the There are two types of nuclear division mitosis and meiosis As in binary fission mitosis is a form of asexual reproduction that results in two genetically identical daughter cells Mitosis refers to nuclear division karyokinesis but usually division of the cytoplasm cytokinesis accompanies or immediately follows mitosis so the result is two daughter cells that are genetically identical to the parent cell Embryological development asexual reproduction regeneration and maintenance or repair of body tissues are all accomplished by mitotic division and cytokinesis Cell Division I The Cell Cycle and Mitosis The cell cycle begins with the formation of a new cell and ends when that cell replicates Interphase G1 or first gap interval of interphase occurs immediately after mitosis This is the primary growth period On average the lifespan of a cell is 22 hours of which
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