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Chloroplast were first reported or identified by Julius Von Sachs and the term
chloroplast was coined by Schimper in 1883.
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The word Chloroplast is derived from the Greek word Chloros
which mean “green” and Plastes
which means “the one who forms”.
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Chloroplast (Cell organelle) is a Green coloured plastid in the cells of green plants
and green algae that contains Chloroplyll pigment
and creates glucose/starch through photosynthesis.
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Chloroplast are found in all green parts of plants
like leaves, young branches, stem, Calyx/sepals, unripe fruits etc
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Chloroplasts are spherical or oval or disc shape
which are green in colour due to chlorophyll pigment.
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Chloroplast is a membrane bound structure consisting of three membranes – Outer
membrane, Inner membrane and third
internal membrane is Thylakoid membrane ( Grana).
(i) Outer Membrane :
The outer
membrane act as protective layer which is permeable to small organic
molecules and ions which diffuses easily and outer membrane is not permeable to
larger proteins.
(ii) Inner membrane:
Inner
membrane consist of Stroma and Grana
The
intermediary fluid filled portion is called Stroma.
It responsible for enzymatic reactions leading to synthesis of glucose, which
in turn join together to form starch.
The
inner membrane is less permeable and covers with proteins. Dark reaction occurs in Stroma region.
(iii) Thylakoid Membrane :
The
third layer forms stacked Sac (bag or pouch)
like structures called as Thylakoid or Grana (plural). It helps to trap the solar energy
which are connected by Stroma lamellae / Stroma
thylakoid. Light
reaction occurs in Grana region.
-The
space within a thylakoid is called Lumen.
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Substances found in chloroplast which capture sunlight are called Photosynthetic pigments. There are several types of
photosynthetic pigments involved in the process to produce organic molecules
like glucose in plants.
-Chlorophyll
is a pigment which contain one atom of magnesium. Two major kinds of
chlorophylls are associated with thylakoid membranes. Chlorophyll ‘a’ is Blue-green in colour and chlorophyll ‘b’ is Yellow-green colour.
-Around
250 to 400 pigment molecules are grouped as light harvesting complex or
photosynthetic unit in each thylakoid. Such innumerable units function together
in chloroplasts of green plants in the process of photosynthesis.
-During photosynthesis several events occur in the chloroplast
some of them are :
(i)
Conversion of light energy to chemical energy.
(ii)
Splitting of water molecule ( Photolysis of water).
(iii)
Reduction of Carbondioxide to Carbohydrates.
·
NOTE
:{ In eukaryotic cell - Mitochondria and Chloroplast are “Semi autonomous organelles” as it
possess its own DNA. Semi
autonomous organelles are organelles with DNA. The Presence of DNA in the
chloroplast helps in self duplication. Hence chloroplasts are called
“Semi-autonomous organelles.”}
Structure of Chloroplast
MECHANISM OF PHOTOSYNTHESIS ( LIGHT AND DARK REACTION)
LIGHT REACTION | DARK REACTION
|
1. Light Dependent Reaction | 1. Light Independent Reaction |
2. Photo Chemical Phase | 2.Biosynthetic Phase |
3. It requires Sunlight | 3.It requires or does not requires Sun light |
4. Occurs in Grana region | 4.Occurs in Stroma region |
5. Photolysis process takes place | 5.Carbon fixation process takes place |
6. ATP and NADPH2 are formed | 6.ATP and NADPH2 are utilized |
7. Oxidative Process | 7. Reductive Process |
8. Electrons are released | 8.Electrons are utilized |
9. End Product are Oxygen, water. | 9.End product is Glucose |
10. It involve Photolysis or Hills reaction H2O → H+ + OH- (water) → ( Hydrogen ion) + ( Hydroxyl ion) | 10.It involves Dark reaction or carbon fixation
H+ + NADP → NADPH
NADPH+ + CO2 →↓ Glucose (ATP Energy) |
