Photosynthesis in Plants

Joseph Priestley conducted experiments in 1774 showing that plants restore the air that has been 'injured' by burning candles or breathing animals, demonstrating the role of plants in gas exchange.

The Emerson effect is the increase in rate of photosynthesis after exposure to light of wavelength 670 nm far red light and 700 nm, red light respectively. When simultaneously exposed to light of both wavelengths, the rate of photosynthesis is far higher than the sum of red light and far red light photosynthesis rates. The effect was early evidence, that photosystems processing different wavelengths cooperate in photosynthesis. 

Chlorophyll is the liquid substance in a plant cell, which is responsible for its colour. Plants make food when sunlight strikes chlorophyll. Pelletier and Caventou discovered chlorophyll in 1818.

Jan Ingenhousz demonstrated that sunlight is essential to the plant process by showing that aquatic plants produce bubbles in the presence of light but not in the dark.

T. W. Engelmann experimented on Cladophora. Using a prism, he split light into its spectral components and then he illuminated a green alga, Cladophora, placed in a suspension of aerobic bacteria. The bacteria were used to detect the sites of oxygen evolution. He found that the bacteria accumulated mainly in the region of blue and red light of the split spectrum. Thus, action spectrum of photosynthesis was first studied by Engelmann.

Theodor Wilhelm Engelmann was a German scientist. In 1883, he performed his famous action spectrum experiment to learn which wavelengths or colour of light were the most effective in carrying out photosynthesis in the green alga.

A) Joseph Priestley first discovered oxygen and discovered that it is released by plants.
B) Jan Ingenhousz proved that sunlight is essential for photosynthesis.

Boussingault was a  French chemist and he made a very significant contribution to the fields of agricultural science and metallurgy.

Photosynthesis takes place in the green leaves of plants and other green parts of plants like stem etc. The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialized light absorbing pigments. These pigments are known as photosynthetic pigments. Chlorophyll and carotenoids are the types of photosynthetic pigments. Chlorophyll is the primary pigment and carotenoids are the accessory pigments. Chemistry of photosynthetic pigments was first studied by Willstatter and Stoll in 1912. They discovered that chlorophyll has a tadpole-like configuration. It has a head called porphyrin and a tail made up of long chain alcohol called phytol. Porphyrin head is made up of four pyrrole rings which are linked by methine bridges. 5 atoms— 4 carbon and one nitrogen form the skeleton of each pyrrole ring. Nitrogen lies towards the centre. Thus, the correct answer is option A.

• F.F. Blackman, a British plant physiologist discovered that photosynthesis is a two-step process and only one of which uses light directly.
• Hill discovered that green particles obtained from broken cells could produce oxygen from water in the presence of light and a chemical compound, such as ferric oxalate, able to serve as an electron acceptor. This process is known as Hill reaction.
• Benson was the co-researcher of Calvin who discovered the Calvin cycle in photosynthesis.
• The process of photosynthetic photophosphorylation was discovered by Arnon. Photosynthetic photophosphorylation is the process of phosphate group transfer into ADP to synthesize energy-rich ATP molecules making use of light as an external energy source. So, this option is correct.

The first photosynthetic organisms to appear on Earth were likely anaerobic bacteria, which evolved the ability to use light energy before the development of oxygenic photosynthesis in cyanobacteria.

Peter Dennis Mitchell, was a British biochemist who was awarded the 1978 Nobel Prize for Chemistry for his discovery of the chemiosmotic mechanism of ATP synthesis. 

Julius Robert von Mayer was a German physician and physicist. He was the first to state the law of the conservation of energy i.e., energy is neither created nor destroyed. He stated that the sun is the ultimate source of energy for both plants and animals and that when absorbed plants convert this light energy through the process of photosynthesis.

Photosynthesis is a process by which green plants manufacture their food with the help of carbon dioxide and water in the presence of sunlight. When light energy is absorbed by photosynthetic pigment chlorophyll, then it gets exited and photosynthetic reaction center loses an electron. In this way, light energy is converted to chemical energy. Conversion of light energy into chemical energy is the primary event in photosynthesis. R. Mayer stated that in photosynthesis light energy is converted into chemical energy. He also proposed that the sun is the ultimate source of energy utilized by living organisms.

• Most of the experimental work in photosynthesis has been done on Chlorella. Through photosynthesis it multiplies rapidly, requiring only carbon dioxide, water, sunlight and a small number of minerals to reproduce. 
• It is easy to culture and it is easy to understand the photosynthetic process in chlorella cells.
•  Based on the above advantages most of the photosynthetic work was conducted in chlorella compared to hydrilla, spinach leaves, and Chlamydomonas.