BISC 101 Lecture Notes - Lecture 22: Light-Dependent Reactions, Chlorophyll, Leaf

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BISC 101 – Lecture 22 – Photosynthesis: Part I
Feeding the Biosphere
Photosynthesis: The process that converts solar energy into chemical energy
Photosynthesis occurs in plants, algae, certain other protists, and some
prokaryotes
Directly or indirectly, photosynthesis nourishes almost the entire living world
Autotrophs: Organisms that sustain themselves without eating anything derived
from other organisms
oThey are the producers of the biosphere
oThey produce organic molecules like CO2 and other inorganic molecules
Photoautotrophs: Organisms that use the energy of sunlight to make organic
molecules from H2O and CO2
oAlmost all plants are photoautotrophs
Heterotrophs: Organisms that obtain organic material from other organisms
oThey are the consumers of the biosphere
oAlmost all heterotrophs, including humans, depend on photoautotrophs for
food and O2
Players of Photosynthesis
Photosynthesis converts light energy to the chemical energy of food
There are about half a million chloroplasts per square millimeter of leaf surface
Leafs are the major site of photosynthesis for most plants
All green parts of a plant have chloroplast
Stroma: Central aqueous space of chloroplast
Stomata: Microscopic pores found in a leaf
oCO2 enters and O2 exits leaf through during photosynthesis
Each chloroplast has two membranes surrounding a stoma
Thylakoids: Elaborate system of interconnected membranous sacs found in the
stoma of chloroplast
Thylakoid Space: The interior of thylakoids that form a space or compartment
oGranum: Stacked columns of thylakoids
Chlorophyll: Green pigment within chloroplast which make up the green color of
leaves
oChlorophyll plays an important role in the absorption of light energy during
photosynthesis
Chloroplasts mainly found in mesophyll
oMesophyll: Tissue which forms the interior of leaf tissue
oA typical mesophyll cell has about 30-40 chloroplasts
Veins deliver water from the roots and carry off from mesophyll cells to non-
photosynthetic areas of the plant
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