What is the chemical
process of photosynthesis? What does in need? What does it make?
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(2) What is the
chemical process of photosynthesis?
You need four 'basic' things for photosynthesis:
(i) water - absorbed through the roots,
(ii) carbon dioxide - absorbed from air by
(iii) chlorophyll - green pigment in palisade
cells of stems and leaves,
(iv) visible sunlight energy - converted to chemical
potential energy in glucose molecules.
Obviously other nutrients are needed as
well, including the magnesium ion, Mg2+, which is
an essential part of the chlorophyll molecule.
A simplified version of the
biochemistry of photosynthesis
Plants absorb water through their
roots and carbon dioxide through their leaves and covert these into
carbohydrate molecules, initially in the form of glucose, the waste
product is oxygen! handy for us!
The carbon dioxide in air diffuses into
leaves through the stomata, water comes up from the roots via the xylem tubes, oxygen diffuses
out and sugars are transported around the plant by the phloem tubes.
Carbon dioxide into leaves and oxygen
out of the leaves is an example of gas exchange system on the
surface pores (stomata) of the leaves.
The biochemical process of photosynthesis
takes place in the chloroplasts of plant cells in the green leaves
and stems with the help of green
molecules called chlorophyll.
The chemistry of
Photosynthesis is summarised
by the equation:
carbon dioxide + water == light +
chlorophyll ==> glucose + oxygen
+ 6CO2(g) == sunlight ==> C6H12O6(aq)
is overall an endothermic chemical reaction, energy is taken in,
i.e. sunlight energy
is absorbed in the process of photosynthesis.
is the process by which plants make food, initially in the form of
glucose, for themselves, and for most
animal life, including us too via food chains!
The plant will use some of the glucose
immediately to fuel all the necessary life maintaining processes.
The plant converts some of the glucose
to starch - a chemical potential energy food store for the plant and
animals like us too!
Photosynthesis utilises sunlight
energy to convert carbon dioxide and water into glucose (basis of food)
The green pigment chlorophyll is in
the subcellular structures
called chloroplasts, where photosynthesis takes place in green
All of the
photosynthetic chemistry facilitated by enzymes (biological catalysts).
The chemistry of photosynthesis is very
complicated but it takes place in two main stages.
1. Chlorophyll absorbs a photon of
light energy. This sunlight energy (visible light
photons) splits water (H2O) into hydrogen ions (H+)
and oxygen (O2).
2. The hydrogen ions combine with carbon
dioxide (CO2) to form glucose molecules (C6H12O6).
The carbon dioxide diffuses in
through the stomata of the guard cells - effectively pores that can open and
close ie CO2 in, and oxygen O2 out in the day and O2
in at night.
In daylight the rate of photosynthesis
will exceed the rate of respiration.
At night the rate of respiration will
exceed that of photosynthesis.
Both processes are need to keep the plant
During photosynthesis light energy is absorbed by
the green chlorophyll, which is
found in chloroplasts in some plant cells and algae.
Keywords, phrases and learning objectives for this part on
Be able to describe in words and equations the
chemical process of photosynthesis?
Know hat is needed for photosynthesis i.e. water
carbon dioxide sunlight chlorophyll and what is produced i.e.
glucose and the 'waste' product oxygen gas.
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