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Chapter 10

BIL 150 Chapter Notes - Chapter 10: Cellular Respiration, Leaf, Photosynthesis


Department
Biology
Course Code
BIL 150
Professor
Gaines Michael
Chapter
10

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Chapter 10: Photosynthesis
Photosynthesis is the conversion process from light energy (sun) to
chemical energy that is stored in sugar and other organic molecules
An organism acquires the organic compounds it uses for energy and
carbon skeletons by one of two major modes: autotrophic nutrition or
heterotrophic nutrition
oAutotrophs are self-feeders, meaning they sustain themselves
without eating anything derived from other living beings
Autotrophs produce their organic molecules from CO2 and
other inorganic raw materials obtained from the environment
Autotrophs are the ultimate sources of organic compounds
for all non-autotrophic organisms, and are referred to as the
producers of the biosphere
oHeterotrophs obtain organic material by the second major mode of
nutrition, as they are unable to make their own food they live on
compounds produced by other organisms
The consumers of the biosphere
Chloroplasts are the sites of photosynthesis in plants
oChloroplasts are found mainly in the cells of the mesophyll, the
tissue in the interior of the leaf
oCarbon dioxide enters the leaf, and oxygen exits by way of
microscopic pores called stomata

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oA chloroplast has an envelope of two membranes surrounding a
dense fluid called the stroma
oSuspended within the stroma is a third membranes system, made
up of sacs called thylakoids, which segregates the stroma from the
thylakoid space inside these sacs
Thylakoid sacs are stacked in columns called grana
(granum)
oChlorophyll, the green pigment that gives leaves their color,
resides in the thylakoid membranes of the chloroplast
The equation of photosynthesis
o6 CO2 + 6 H2O + Light energy  C6H12O6 + 6 O2
Carbon dioxide + water + light energy = glucose + oxygen
The reverse of cellular respiration
Photosynthesis as a redox process
oWater is split, and electrons are transferred along with hydrogen
ions from the water to carbon dioxide, reducing it to sugar

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oBecause the electrons increase in potential energy as they move
from water to sugar, this process requires energy (endergonic
process)
Energy is provided by light
Light reactions are the steps of photosynthesis that convert solar energy
to chemical energy (occurs in the thylakoids of the chloroplasts)
oWater is split, providing a source of electrons and protons
(hydrogen ions H+) and giving off O2 as a by-product
oLight absorbed by chlorophyll drives a transfer of the electrons and
hydrogen ions from water to an acceptor called NADP+, where they
are temporarily stored
oThe light reactions use solar energy to reduce NADP+ to NADPH by
adding a pair of electrons along with an H+
oThe light reactions also generate ATP, using chemiosmosis to
power the addition of a phosphate group to ADP, a process called
photophosphorylation
oTherefore, light energy is initially converted to chemical energy in
the form of two compounds: NADPH and ATP
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