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Chloroplast
In a nutshell:
Site of photosynthesis
Additional information:
Plant cells normally contain another type of organelle that is not found in animals:chloroplasts.
Chloroplasts convert light energy (from the sun) to chemical energy via the process of photsnthesis
. The main pigment (green color) located in chloroplasts and involved in photosynthesis is
chlorphyll Chloroplasts are surrounded by an outer membrane and inner membrane separated by
an intermembrane space. The fluid within the center of the chloroplast is called stroma. Within this
fluid is an interconnected system of stacks of disks, kind of like more water-balloon-pancakes. Each
sack is called a thylakoid. and has chlorophyll and other useful pigments built into its membranes.
A stack of thylakoids is called a granum.
What's most important?
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Chloroplasts are the site of photosnythesis in eukaryotic cells.
Chloroplasts are disk-like structures composed of a single membrane surrounding a fluid
containing stacks of membranous disks.
Because of their green color chloroplast are the only organelles that can be easily seen with a
light microscope.
Structure
There is a single membrane surrounding the chloroplast. This membrane surrounds a fluid called
the stroma. Floating in the stroma are stacks of disks made up of membranes, these are the grana.
The grana resemble a stack of coins, however instead of coins this stack is made up of individual
hollow disks called thylakoids.
This electronmicrograph shows a chloroplast in cross section. Note the ligher colored liquid stroma
and the stacks of membranous disks known as grana.
Chlorophyll, the green compound that gives chloroplasts their color, is found in the membranes of
the thylakoids.
Function
Chloroplasts are the site of photosynthesis in eukaryotic cells. The light reactions take place on the
membranes of the grana. The dark reactions(also called light-independent reactions and/or CalvinBenson Cycle) take place in the stroma.
Details
Chloroplasts like mitochondria contain their own DNA and reproduce themselves. Both
mitochondria and chloroplasts have these charactristics of prokaryotes(bacteria) this and other
evidence has led biologists to formulated the endosymbiotic hypothesis. The endosymbiotic
hypothesis states that mitochondria and chloroplasts evolved from free-living bacteria which took
up residence inside other cells. You can read more about this hypothesis in newer biology books or
newer encyclopedias.