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Transcript
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