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Summary CONCEPT- Photosynthesis
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It is a detailed typed word document about one of the most important topics - photosynthesis. this note includes simple conceptual diagrams and conceptual points .
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What is photosynthesis? The process of synthesis with the assistance of light is termed
as photosynthesis.
It is the mechanism by which sunlight is used by green plants to produce food
from simple molecules like CO2 and H2O.
Often called carbon assimilation, photosynthesis is expressed by the following
equation;
6CO2 + 6H2O——— > C6 H12 O6 + 6O2
The light energy is transformed into chemical energy during the
photosynthesis process and is stored into the organic matter, which is
normally carbohydrates, and O2 is a by-product of photosynthesis.
The raw materials for this process are CO2 and H2O.
CO2 from the air and H2O from the soil are absorbed.
The following points make photosynthesis essential to humanity:
It preserves the atmospheric equilibrium of O2.
It provides food either directly as vegetables or indirectly as animal meat or
milk which, in turn, is fed to plants.
Where does photosynthesis takes place?
The photosynthesis occurs in chloroplasts in case of plants and blue-green
algae.
When microscopic observation of a leaf section is done, chlorophyll is not
uniformly distributed in the cell.
However, it is confined to organelles termed as chloroplasts.
In plants, chloroplasts lie mainly in the cells of mesophyll, a layer that includes
several air spaces and a very high concentration of water vapor.
The exchange of gases takes place between interior of the leaf and the outside
through microscopic pores, termed as stomata.
Each mesophyll cell consists of 20-100 chloroplasts.
The chloroplast is enclosed by outer and inner membranes.
The inner membrane encloses a fluid filled region termed as stroma.
Stroma consists of most of the enzymes needed to produce carbohydrate
molecules.
The third system of membranes is suspended in the stroma.
This system forms an interconnected set of flat, disc like sacs called thylakoids.
A fluid-filled internal space, the thylakoid lumen, is enclosed by the thylakoid
membrane.
Thylakoid sacs are arranged in stacks called grana (sing., granum) in some
regions of the chloroplast.
Each granum is identical to a coin stack, with a thylakoid being each “coin.”
, Some thylakoid membranes extend from one granum to another.
Thylakoid membranes are involved in ATP synthesis.
Photosynthetic pigments:
There are major three photosynthetic pigments. They are:
Chlorophylls
Carotenoid
Phycobillins
i. Chlorophylls:
Chlorophylls are present in thylakoid membranes.
Thylakoid membranes consist of several kinds of pigments that absorb visible
light.
Various pigments absorb light from various wavelengths.
Chlorophyll is the dominant photosynthesis pigment and it absorbs light
mainly in the visible spectrum’s blue and red areas.
Green light is not appreciably absorbed by chlorophyll.
Some of the green light that strikes the plant is either scattered or reflected
and hence the plants typically appear to be green in colour.
There are two principal parts of a chlorophyll molecule, a complex ring and a
long side chain.
A porphyrin ring is ring structure that comprises of smaller rings made of
carbon and nitrogen atoms.
The porphyrin ring absorbs light energy.
The chlorophyll porphyrin ring is remarkably similar to the red pigment
hemoglobin component of the heme in red blood cells.
However, unlike heme, that holds an atom of iron in the center of the ring,
chlorophyll consists of an atom of magnesium in that position.
The chlorophyll molecule also contains a long, hydrocarbon side chain that
makes the molecule extremely nonpolar and ties up the chlorophyll in the
membrane
All chlorophyll molecules in the thylakoid membrane are associated with
specific chlorophyll-binding proteins
Each thylakoid membrane is filled with accurately oriented chlorophyll
molecules and chlorophyll-binding proteins that facilitate the transfer of
energy from one molecule to another.
There are many kinds of chlorophyll.
The chlorophyll ‘a’ is the most essential pigment that starts the light-
dependent reactions of photosynthesis.
Chlorophyll ‘b’ is the accessory pigment which also takes part in
photosynthesis.
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