Revision notes for Photosynthesis in higher plants (STD 11).
Answers
Photosynthesis : Photosynthesis is an enzyme regulated anabolic process of manufacture of organic compounds inside the chlorophyll containing cells from carbon dioxide and water with the help of sunlight as a source of energy.
Photosynthesis takes place only in green parts of plants mostly in leaves. Within a leaf, photosynthesis occurs in mesophyll cells which contain the chloroplasts. Chloroplasts are the actual sites for photosynthesis. The thylakoids in chloroplast contain most of pigments required for capturing solar energy to initiate photosynthesis. The membrane system (grana) 2 is responsible for trapping the light energy and for the synthesis of ATP and NADPH. Biosynthetic phase (dark reaction) is carried in stroma.
" Pigments involved in photosynthesis "
Chlorophyll a : (Bright or blue green in chromatograph). Major pigment, act as reaction centre, involved in trapping and converting light into chemical energy.
Chlorophyll b : (Yellow green)
Xanthophyll : (Yellow)
Carotenoids : (Yellow to yellow-orange) In the blue and red regions of spectrum shows higher rate of photosynthesis.
Process of photosynthesis : It includes two phases - Photochemical phase and biosynthetic phase.
(i) Photochemical phase (Light reaction) :This phase includes - light absorption, splitting of water, oxygen release and formation of ATP and NADPH.
(ii) Biosynthetic phase (Dark reaction) : It is light independent phase, synthesis of food material (sugars).
Photophosphorylation : The process of formation of high-energy chemicals (ATP and NADPH).
Non-cyclic photophosphorylation : Only PSI works, the electron circulates within the photosystem. It happens in the stroma lamellae (possible location) because in this region PSII and NADP rectase enzyme are absent. Hence only ATP molecules are synthesised.
The electron transport (Z-Scheme) : In PS II, reaction centre (chlo. 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 down hill. Then, the electron pass to PSI and move down hill further.
The splitting of water : It is linked to PS II. Water splits into H , O and electrons.
Factors affecting photosynthesis :
1. Light
2. Carbondioxide
3. Temperature
4. Water
see ncerthelp.com for more detailed notes!