chp 6 notes.docx

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18 Apr 2012
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Heterotrophs:
Organisms that depend on an external source of organic compounds
Autotrophs:
Organisms capable of surviving on CO2 as their principal carbon source
2 types of autotrophs:
Chemoautotrophs: utilize the chemical energy stored in organic molecules to convert CO2 into
organic compounds.
Photoautotrophs: utilize the radiant energy of the sun to convert CO2 into organic compounds.
Photosynthesis:
a process in which energy from sunlight is transformed into chemical energy that is stored in
carbohydrates and other organic molecules.
During photosynthesis, relatively low-energy electrons are removed from a donor compound and
converted into high-energy electrons using the energy absorbed from light.
Extensive genetic analyses of chloroplast genomes suggest that all modern chloroplasts have arisen
from a single, ancient symbiotic relationship. As a result of their common ancestry, chloroplasts and
cyanobacteria share many basic characteristics, including a similar photosynthetic machinery
Chloroplasts are located predominantly in the mesophyll cells of leaves.
Chloroplasts of higher plants are generally lens-shaped approximately 2 to 4m wide and 5 to 10m
long, and typically numbering 20 to 40 per cell.
chloroplasts arise by fission from preexisting chloroplasts (or their nonpigmented precursors, which
are called proplastids).
Chloroplasts were identified as the site of photosynthesis in 1881 in an ingenious experiment by the
German biologist T. Engelmann.
The outer covering of a chloroplast consists of an envelope composed of two membranes separated
by a narrow space
the outer membrane of a chloroplast envelope contains several different porins
The inner membrane of the envelope is highly impermeable; substances moving through this
membrane do so only with the aid of a variety of transporters.
Much of the photosynthetic machinery of the chloroplastincluding light-absorbing pigments, a
complex chain of electron carriers, and an ATP-synthesizing apparatusis part ofan internal
membrane system that is physically separate from the double-layered envelope.
The internal membrane of thechloroplast, which contains the energy-transducing machinery,is
organized into flattened membranous sacs, called thylakoids.
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