In Greek,the word photosynthesis
where the word photo (light) and
A process used by plants and other
organisms to convert the light
energy captured from the sun into
chemical energy that can be used
to fuel the organism's activities.
Occurs in plants,algae, and many species
of bacteria, but not in archae (a kind of single
celled microorganism). Photosynthetic organisms
are called photoautotrophs, since they can
create their own food.
In plants, algae, and cyanobacteria,
photosynthesis uses carbon dioxide and
water, releasing oxygen as a waste product.
Photosynthesis is vital for all aerobic life on
Earth. In addition to maintain normal levels of
oxygen in the atmosphere, photosynthesis is the
source of energy for nearly all life on earth
Jean Baptiste van Helmont conducted an experiment to find
how plant grew.He finally concluded that the plant had grown
mainly form the water which was added regularly and not the
Joseph Priestly demonstrated that plants could restore oxygen
and were capable of supporting combustion and
respiration.Priestly did not know about oxygen but his work
showed that plants release oxygen into atmosphere.
Jan Ingenhousz recognised the importance of sunlight and
chlorophyll in photosynthesis.
Robert Meyer recognised that plant convert solar energy into
chemical energy during photosynthesis
Blackman solved the mystery of photosynthesis.He
discovered that photosynthesis involves two principle
The process always begins when energy
from light is absorbed
by proteins called photosynthetic reaction
centers that contain chlorophylls.
In plants, these proteins are held
inside organelles called chloroplasts, while in
bacteria they are embedded in the plasma
membrane. Some of the light energy
gathered by chlorophylls is stored in the form
of adenosine triphosphate (ATP).
The rest of the energy is used to
remove electrons from a substance such as
water. These electrons are then used in the
reactions that turn carbon dioxide into organic
In plants, algae and cyanobacteria, this is
done by a sequence of reactions called
the Calvin cycle.
Photosynthetic organisms are photoautotrophs,which means that
they are able to synthesize food directly from carbon dioxide and
water using energy from light.
However, not all organisms that use light as a source of energy
carry out photosynthesis, since photoheterotrophs use organic
compounds, rather than carbon dioxide, as a source of carbon.
In plants, algae and cyanobacteria, photosynthesis releases
oxygen. This is called oxygenic photosynthesis. Although there
are some differences between oxygenic photosynthesis
in plants,algae, andcyanobacteria, the overall process is quite
similar in these organisms.
However, there are some types of bacteria that carry
out anoxygenic photosynthesis, which consumes carbon dioxide
but does not release oxygen.
Carbon dioxide is converted into sugars in a process
called carbon fixation. Carbon fixation is a redox reaction, so
photosynthesis needs to supply both a source of energy to drive
this process, and the electrons needed to convert carbon dioxide
into a carbohydrate, which is a reduction reaction.
In general outline, photosynthesis is the opposite of cellular
respiration, where glucose and other compounds are oxidized to
produce carbon dioxide, water, and release chemical energy.
However, the two processes take place through a different
sequence of chemical reactions and in different cellular
Plants take up water
from the soil to their
Plants will also absorb
carbon dioxide from the
atmosphere to be able to
carry out photosynthesis.
Sunlight is very vital to
plant to be converted in
The end product would
be glucose which provide
energy for plant and
oxygen which benefits
human for respiration.
Air space - intercellular gaps within the spongy mesophyll.
These gaps are filled with gas that the plant uses (carbon
dioxide - CO2 ) and gases that the plant is expelling (oxygen -
O2, and water vapor).
Chlorophyll - a molecule in leaves that can use light energy
from sunlight to turn water and carbon dioxide gas into sugar
and oxygen (this process is called photosynthesis).
Chlorophyll is magnesium-based and is green.
Cuticle - the waxy, water-repelling layer on the outer surface
of a leaf that helps keep it from dying out (and protect it from
invading bacteria, insects, and fungi). The cuticle is secreted
by the epidermis (including the guard cells) and is often
thinner on the underside of leaves. The cuticle is generally
thicker on plants that live in dry environments.
Epidermis - the protective, outler layer of cells on the
surface of a leaf. The guard cells (and stoma) are part of the
epidermis. The surface of many leaves is coated with a waxy
cuticle which is secreted by the epidermis.
Guard cell - one of a pair of sausage-shaped cells that surround a
stoma (a pore in a leaf). Guard cells change shape (as light and
humidity change), causing the stoma to open and close.
Palisade mesophyll - a layer of elongated cells located under the
upper epidermis. These cells contain most of the leaf's chlorophyll,
converting sunlight into usable chemical energy for the plant.
Spongy mesophyll - the layer below the palisade mesophyll; it has
irregularly-shaped cells with many air spaces between the cells.
These cells contain some chlorophyll. The spongy mesophyll cells
communicate with the guard cells (stomata), causing them to open
or close, depending on the concentration of gases.
Stoma - (plural stomata) a pore (or opening) in a plant's leaves
where water vapor and other gases leave and enter the plant.
Stomata are formed by two guard cells that regulate the opening
and closing of the pore. Generally, many more stomata are on the
bottom of a leaf than on the top.
Vein (vascular bundle) - Veins provide support for the leaf and
transport both water and minerals (via xylem) and food energy (via
phloem) through the leaf and on to the rest of the plant.