1. CHLOROPLAST
Chloroplasts are organelles found in
plant cells and other eukaryotic organisms that
conduct photosynthesis . The word chloroplast
is derived from the Greek words chloros, which
means green, and plast, which means form or
entity. Chloroplasts are members of a class of
organelles known as plastids. are considered to
have originated from cyanobacteria through
endosymbiosis. This was first suggested by
Mereschkowsky in 1905[2] after an observation
by Schimper in 1883 that chloroplasts closely
resemble cyanobacteria .

2. • The endosymbiotic theory concerns the origins
of mitochondria and plastids (e.g. chloroplasts),
which are organelles of eukaryotic cells.
According to this theory, these organelles
originated as separate prokaryotic organisms
that were taken inside the cell as endosymbionts.
Mitochondria developed from proteobacteria (in
particular, Rickettsiales or close relatives) and
chloroplasts from cyanobacteria. Chloroplasts
are observable as flat discs usually 2 to 10um
diameter and 1um thick. In land plants, they are,
in general, 5 μm in diameter and 2.3 μm thick.

3. • The chloroplast is contained by an envelope that
consists of an inner and an outer phospholipid
membrane. Between these two layers is the
intermembrane space. A typical parenchyma cell
contains about 10 to 100 chloroplasts. The
material within the chloroplast is called the
stroma, and contains one or more molecules of
small circular DNA. It also contains ribosomes;
however most of its proteins are encoded by
genes contained in the host cell nucleus, with the
protein products transported to the chloroplast.

6. • Within the stroma are stacks of thylakoids, the
sub-organelles, which are the site of
photosynthesis. The thylakoids are arranged in
stacks called grana (singular: granum).[1] A
thylakoid has a flattened disk shape. Inside it is
an empty area called the thylakoid space or
lumen. Photosynthesis takes place on the
thylakoid membrane; as in mitochondrial
oxidative phosphorylation, it involves the
coupling of cross-membrane fluxes with
biosynthesis via the dissipation of a proton
electrochemical gradient .

7. • , Thylakoid membranes appear as alternating
light-and-dark bands, each 0.01 μm thick.
Embedded in the thylakoid membrane are
antenna complexes, each of which consists of the
light-absorbing pigments, including chlorophyll
and carotenoids, as well as proteins that bind the
pigments. This complex both increases the
surface area for light capture, and allows capture
of photons with a wider range of wavelengths. The
energy of the incident photons is absorbed by the
pigments and funneled to the reaction centre of
this complex through resonance energy transfer.
Two chlorophyll molecules are then ionised,
producing an excited electron, which then passes
onto the photochemical reaction centre.

8. CHLOROPLAST MEMBRANE
• chloroplasts have a double-membrane
envelope, called the chloroplast envelope.
Each membrane is a phospholipid bilayer,
between 6 and 8 nm thick, and the two are
separated by a gap of 10-20 nm, called the
intermembrane space. The outer membrane is
permeable to most ions and metabolites, but the
inner membrane is highly specialised with
transport proteins. Carbohydrates are
transported across the outer membrane by a
triose phosphate translocator.

9. • Chloroplast in Plageconium cell

10. • Chloroplast in Plageconium cell