covering completely the material present in Photosynthesis
animation the advanced photosynthesis covers the following
in detail (shown in bold)
Structure of leaf & functioning
Cuticle details: Cuticle is made of cutin,
a tough lipid-like and water inadmissible substance. In
addition to which a waxy layer is often present.
Stoma details and animation of stoma: Stoma consists
of an opening or stomata pore and two kidney-shaped guard
cells. The guard cells don't have muscles, but they can
open and close using fluid pressure.
Mesophyll cells: Mesophyll cells are located in
between the upper and lower epidermis of the plant leaf.
The lower mesophyll cells; spongy parenchyma have large
inter-cellular spaces that facilitate gas diffusion.
Parts of a plant cell
Chloroplast structure with zoom ins: covers Chloroplast
as an organelle, stroma, grana, lamellae, thylakoid and
Chloroplasts have a lens like structure. A mysophyll cell
contains around 50 chloroplasts. Chloroplast contains bodies
located on stroma lamellae called grana. Each granum consists
of many thylakoid placed one above other like stack of coins.
Chlorophyll pigments are studded with the inner surface
The fluid within the chloroplast is called the stroma
Primary and accessory pigments, their light spectra,
comparison, chemical structure, properties and explanations:
Chlorophyll a , chlorophyll b, carotenoids, phycoerythrin
and phycocyanin. Plants are green due to the photosynthetic
pigment chlorophyll. Chlorophyll serves to reflect green
and yellow wavelengths of light and absorb all the others.
Since we perceive primarily reflected colors with our eyes,
plant tend to look green
Why leaves turn yellow in autumn? (Answered in animation)
Chlorophyll exists in two forms, chlorophyll a (the primary
photosynthetic pigment) and chlorophyll b
Photosynthesis is not entirely reflective of the absorption
spectrum of chlorophyll a. This is due to the presence of
accessory pigments such as chlorophyll b, the carotenoids,
phycoerythrin and phycocyanin.
Carotenoids responsible for yellow and orange colour
Phycoerythrin responsible for red colour. For e.g. red algae
Phycoerythrin mostly found in blue algae and blue bacteria
Accessory pigments serve to capture light energy and transfer
this energy to chlorophyll.
Antenna complex or Light Harvesting Complex (LHC) and the
The reaction center:
The LHC is composed of hundreds of molecules of chlorophylls
and accessory pigments. Most of the Chlorophyll a in a cell
is actually involved in light harvesting. These are referred
to as antenna pigments
Why are they called antenna molecules? (Answered
All the pigment molecules in the LHC are constantly absorbing
light, and when light of a certain wavelength (less than
680 nm) is absorbed; the absorbed energy is transferred
from one molecule to another until it reaches the reaction
Types of Photosystems : PSII (P680)
and PSI (P700)
The reaction center consists of one of several different
chlorophyll molecules. The photosystem II has a reaction
center consisting of a chlorophyll A molecule. In plants
there is also a second type of reaction center in photosystem
I, it again has chlorophyll 'a' but it is optimized for
700 nm wavelength of light.
Light Dependent and independent reactions
Photosynthesis is a two-stage process. The first process
is the Light Dependent Process (Light Reactions), requires
the direct energy of light to make energy carrier molecules
that are used in the second process. The Light Independent
Process (or Dark Reactions) occurs when the products of
the Light Reaction are used to form glucose
How transfer of light energy takes place between pigment
molecules? (Answered in animation)
As pigment molecules in the antenna complexes of Photosystem
II absorb photons, the primary electron acceptor of the
Photosystem II electron transport chain picks up excited
electrons from the reaction center. During this process,
Photosystem II splits molecules of H2O into 1/2 O2, 2H+,
and 2 electrons by a process called as photolysis.
How does photolysis of water takes place-using Mn-complex?
(Detailed animation of photolysis)
These electrons continuously replace the electrons being
lost by the P680 chlorophyll a molecules in the reaction
centers of the Photosystem II antenna complexes
Chemiosmosis , electron transport
chain and proton gradient
ATP gets generated by the Photosystem II electron transport
chain (consisting of Cytochrome b6f). According to the chemiosmosis
theory, as the electrons are transported down the electron
transport chain, some of the energy released is used to
pump protons across the thylakoid membrane from the stroma
of the chloroplast to the thylakoid interior space producing
a proton gradient or proton motive force.
ATP Synthesis: As the
accumulating protons in the thylakoid interior space pass
back across the thylakoid membrane to the stroma through
ATP synthetase complexes, this proton motive force is used
to generate ATP from ADP and Pi.
What is H+ ion (proton) pump (answered in animation)
Pigment molecules in the antenna complex of Photosystem
I are also absorbing photons and excited electrons from
the reaction center are picked up by the primary electron
acceptor of the Photosystem I electron transport chain.
The electrons being lost by the P700 chlorophyll a molecules
in the reaction centers of Photosystem I are replaced by
the electrons traveling down the Photosystem II electron
transport chain. The electrons transported down the Photosystem
I electron transport chain combine with 2H+ from the surrounding
medium and NADP+ to produce NADPH + H+.
Detailed Calvin cycle (dark reactions)
This energy rich ATP and NADPH is then send to calvin cycle
in stroma to combine with carbon dioxide (CO2) and water,
producing sugar (glucose). This is light independent step.
This carbon, along with the ATP and NADPH produced from
the light-dependent reactions, is used to form glucose
Calvin cycle starts with carbondioxide, which enters through
stoma of leaf
Carbon dioxide is added to a five-carbon compound termed
ribulose biphosphate (RuBP). The enzyme responsible for
this reaction is termed Rubisco and, without it, photosynthesis
would not be possible.