RAW MATERIALS OF PHOTOSYNTHESIS
Carbon dioxide In land plants, carbon dioxide is obtained from the atmosphere through the stomata. Small quantities of carbonates are also absorbed from the
soil through the roots.Hydrophytes get their carbon dioxide supply from the aquatic environment as bicarbonates, through their general surface Moll's half leaf experiment showed that carbon dioxide is necessary for photosynthesis Water In the process of photosynthesis, the source of liberated oxygen is water. Photosynthetic land plants absorb a large
amount of water from the soil through the root hairs.
But, relatively very small amount of this absorbed water (about 1%) is used in the process of photosynthesis. Aquatic photosynthetic plants absorb water through their body surface.
In 1937, Robin Hill demonstrated that in absence of carbon dioxide, isolated chloroplasts of Stellaria media
produced oxygen when they were illuminated in presence of a hydrogen acceptor (viz., ferricyanide). Here, ferricyanide is reduced to ferrocyanide by photolysis of water. This is Hill reaction and can be represented as 2A + 2H20Lght2AH2+021Chloroplasts
Here, A represents hydrogen acceptor.
The hydrogen acceptor is often called Hill oxidant or Hill reagent.
In plants, NADP+ (nicotinamide adenine dinucleotidephosphate) acts as a hydrogen acceptorLight Chlorophyl In 1941, by using non-radioactive, heavy isotope of oxygen (180), Ruben and Kamen proved that during 6C0+ 12H2100+ 6H,0+ 6 1802t Light photosynthesis, oxygen comes from the water Light Chiorophyll. Light is the visible part of electromagnetic radiations.
Electromagnetic radiations are a form of energy that consistof a stream of tiny particles called photons, which traveln waves.
Sunlight or solar radiations reaching the earth have wavelengths between 300 nm (in the ultraviolet range) to2600 nm (in the infra-red range).Part of the spectrum used in photosynthesis has a wavelength
between 400-700 nm. It is called photosyntheticallye active radiation (PAR).
" Leaves appear green because chlorophylls do not absorb green light, but allow the same to be reflected and transmitted through leaves.
The energy contained in a photon is termed as quantum. Theenergy content of a quantum is related to its wavelength
The shorter the wavelength, the greater is the energy present in its quantum. Quantum energy is measured in the unit called einstein 80-90% of light falling on leaves is absorbed by them. The rest is reflected and transmitted. Most of the absorption.
occurs in red and blue regions.
Blue and red regions of the light spectrum are the most effective in photosynthesis. Blue wavelengths of light carry
more energy while red wavelengths have lesser energy.
The most efficient wavelength of light light effective in photosynthesis is that of red light. Green light is the least effective in photosynthesis.
The light transmitted by the tree canopy is rich in green light. Therefore, plants growing under the canopy of others
have lower rates of photosynthesis.
Chloroplasts=
Chloroplasts are the green plastids which occur in a the green parts of the plants. They are the actual sites of photosynthesis.
They occur mostly in the chlorenchymatous cells (particularly
in mesophyll) of leaves and young stems. Each mesophyll cell may contain as many as 300 chloroplasts in its peripheral cytoplasm Chloroplasts of higher plants are usually discoid, ellipsoidal or biconvex lens shaped. They are usually 4- 10 um in
ength and 1-3 um in breadth. Each chloroplast of higher plant is an organelle with an outer envelope consisting of a double membrane, which acts as a selective barrier to the movement of cellular metabolites into or out of the chloroplasts.
The chloroplast envelope encloses a liquid proteinaceous matrix called stroma. The whole liquid medium of stroma i
hyaline, slightly electron dense, granular matrix and contains all the necessary enzymes of photosynthesis.
The stroma is the site of dark reaction of photosynthesise
° The lamellar system within the stroma forms flattened sac like lamellae called thylakoids (Gk. thylakos sac, oid like). These thylakoids are stacked to form grana.
