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Chlorophyll and Photosynthesis
Ingenhousz wanted to find out more about photosynthesis and carried
out several other experiments. He proposed that only green plant parts
could carry out the process of photosynthesis.
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What about plants having coloured leaves? How is it that new leaves
which look dark red in colour in several plants turn green? Do plants having
reddish or yellowish leaves also carry out photosynthesis? What made
plants carry out photosynthesis while even green coloured animals (like
some birds )could not? Questions like these remained challenges until
scientists could isolate the green coloured substance from plant parts and
study its nature.
8 X Class Nutrition - Food supplying system
Establishment of Ingenhousz’s proposition came after several
experiments till the mid 20th century when scientists could also locate the
site of photosynthesis and even isolate it. Around four decades after
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Ingenhouszs’ proposition scientists could only isolate the green substance
to observe its nature and find out whether photosynthesis could be carried
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out with it. This had become possible in the year 1817 due to the work of
two scientists Pelletier and Caventou who obtained an extract of the green
coloured substance and named it ‘chlorophyll’ meaning green leaf.
It was also found that pigments in addition to chlorophyll, carotenoids
and phycobilins could also aid in the process of photosynthesis by passing
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on the energy of sunlight trapped by them to chlorophyll.
Where does Photosynthesis take place?
Where is chlorophyll and other pigments present in the plant?
Try to name some parts where you think photosynthesis occurs.
Do you think the new reddish leaves of plants also carry out
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photosynthesis? What could be the reason for their colour?
The exact location of the photosynthetic part or a part containing
chlorophyll was not known till another six decades after Pelletier and
Caventou discovered chlorophyll. It was believed to be spread in the cells
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of green plant parts. In 1883, Julius Von Sachs, observed that chlorophyll
in plant cells is not spread through out the entire cell. It is rather found in
organelles within the cell. Such organelles were named as ‘chloroplasts’.
These are present in large numbers in the cells (around 40 – 100) of parts
like the stomatal guard cells and ground tissues of plants .
You have studied about Chloroplast in Class IX. Let us observe the
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figure of TS of leaf showing Chloroplast in Palisade and Spongy
Parenchyma.
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cuticle
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upper epidermis
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palisade parenchyma
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xylem
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Vascular bundle
phloem
spongy parenchyma
air spaces
guard cell
lower epidermis
stomata
fig-7: T-S of leaf cuticle
Free distribution by T.S. Government 2019-20 9
What makes chloroplast appear completely different from other cell
organelles?
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