NCERT Solutions for Class 11 Biology Chapter 13
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Photosynthesis in Higher Plants: Solutions
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Important Notes on Photosynthesis in Higher Plants
- Josheph Priestley (1770): Showed that plants have the ability to take up CO2 from atmosphere and release O2. (Candle with belljar and mouse expt.)
- Jan Ingenhousz (1779): Release of O2 by plants was possible only in sunlight and only by the green parts of plants. (Expt. with aquatic plant in light & dark).
- Theodore de Saussure (1804): Water is an essential requirement for photosynthesis to occur.
- Hill (1937): Evolution of oxygen occurs in light reaction.
- Calvin (1954-55): Traced the pathway of carbon fixation.
- Hatch and Slack (1965): Discovered C4 pathway of CO2 fixation.
- Julius Von Sachs (1854): Green parts in plant produce glucose which is stored as starch.
- T.W. Engelmann (1888): The effect of different wavelength of light on photosynthesis and plotted the first action spectrum of photosynthesis.
- C.B. Van Niel (1931): Photosynthesis is essentially a light dependent reaction in which hydrogen from an oxidisable compound reduces CO2 to form sugar. He gave a simplified chemical equation of photosynthesis.
Light Harvesting Complexes (LHC)
The light harvesting complexes are made up of hundreds of pigment molecules bound to protein within the photosystem I (PS-I) and photosystem II (PS-II). Each photosystem has all the pigments except one molecule of chlorophyll–a – forming a light harvesting system (antennae). The reaction centre (chlorophyll a) is different in both the photosystems.
Two photosystems work in series – First PSII and then PSI. These two photosystems are connected through an electron transport chain (Z. Scheme). Both ATP and NADPH + H+ are synthesised by this process. PSI and PSII are found in lamellae of grana, hence this process is carried here.
The electron transport (Z-Scheme)
In PS II, reaction centre (chlorophyll a) absorbs 680 nm wavelength of red light which make the electrons to become excited. These electrons are taken up by the electron acceptor that passes them to an electron transport system (ETS) consisting of cytochromes. The movement of electron is downhill. Then, the electron pass to PS I and move downhill further.
Only PS-I works, the electron circulates within the photosystem. It happens in the stroma lamellae (possible location) because in this region PSII and NADP reductase enzyme are absent. Hence only
ATP molecules are synthesised. It occurs when only light of wavelengths beyond 680 nm are available for excitation.