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Photosynthetic Organisms SBI 4U Ms.Zafar October 1st, 2012 What is Photosynthesis? • Photosynthesis involves the use of energy from light to form carbohydrates • Organisms that manufacture their own food, do so through photosynthesis (with some exceptions) Photosynthetic Organisms • Autotrophs such as: plants, algae, some protists and cyanobacteria • Contain pigment chlorophyll • Believed to have originated in bacteria modern cyanobacteria Chlorophyll • Made up of porphyrin ring attached to a long hydro-carbon tail • Porphyrin ring is a naturally occurring organic compound • Contains a magnesium atom at its center Prokaryotic Autotrophs: Cyanobacteria • Cyanobacteria: Obtain their energy through photosynthesis. Most abundant photosynthesizing prokaryotes • Aquatic • Probably the first organisms to use sunlight for energy paved way for heterotrophic life • Endosymbiotic Theory Eukaryotic Autotrophs: Algae, Photosynthetic Protists, and Plants • Algae, some protists and plant cells contain chlorophyll within the photosynthetic membranes of organelles called chloroplasts • Since chloroplasts are found only in leaves, stems and fruit these are the only photosynthesizing parts of a plant Leaves: The Photosynthetic Organs of Plants • Usually thin and broad or thin and narrow • Maximum surface area exposed • Primary function of leaves: photosynthesis Structure of a Leaf • Cuticle: protective waxy covering • Epidermis Layer: Allows light to pass through to the mesophyll cells where photosynthesis takes place • Mesophyll Layer: Where chloroplasts are situated • Guard cells: Create microscopic openings called somata that regulate the exchange of CO2 and Oxygen Transpiration • Transpiration: loss of water vapor from plants similar to evaporation • Cuticle and stomata control water loss by transpiration • Dew in the morning Transpiration & Photosynthesis Transpiration helps photosynthesis in 2 ways: • Transpiration pull helps move water, minerals and other substances from roots (where they are absorbed) to leaves (where they are used) • Produces an evaporative cooling effect that prevent leaves from heating Stomata • Guard cells control the size of stomata • Stomata open when guard cells are turgid (swollen) • Stomata close when guard cells are flaccid (limp) • As K+ ions move into guard cells, H2O follows Structure of Chloroplasts • Photosynthesis factories of plants and algae • Inner membrane and an outer membrane enclosing material called stroma • Within stroma are membrane bound sacs called thylakoids form columns called grana • Adjacent grana are connected by lamellae Structure of Chloroplasts, Continued… • Photosynthesis occurs within the stroma and thylakoid membrane • Thylakoid membrane contains lightgathering pigment molecules and ETC • Thylakoid membrane encloses the thylakoid lumen site of ETC • Surface area
