water, mineral and pollutants. II. Internal factors: Pigments, protoplasmic factor, accumulation of carbohydrates, anatomy of leaf and hormones. A B C D HIGH LIGHT INTENSITY MEDIUM LIGHT INTENSITY LOW LIGHT INTENSITY CO CONCENTRATION RATE OF PHOTOSYNTHESIS Figure .
: Blackman’s Law of Limiting Factors . . . External factors .
Light Energy for photosynthesis comes only from light. Photooxidation of water and excitation of pigment molecules are directly controlled by light. Stomatal movement leading to diffusion of CO is indirectly controlled by light. .
Accumulation of Carbohydrates Photosynthetic end products like carbohydrates are accumulated in cells and if translocation of carbohydrates is slow then this will affect the rate of photosynthesis. . Anatomy of leaf Thickness of cuticle and epidermis, distribution of stomata, presence or absence of Kranz anatomy and relative proportion of photosynthetic cells affect photosynthesis. .
Hormones Hormones like gibberellins and cytokinin increase the rate of photosynthesis. . Photosynthesis in bacteria Though we study about bacterial photosynthesis as the last part, bacterial photosynthesis formed first and foremost in evolution. Bacteria does not have specialized structures like chloroplast.
It has a simple type of photosynthetic apparatus called chlorosomes and chromatophores (Table . ). Van Neil ( ) discovered a bacterium that releases sulphur instead of oxygen during photosynthesis. Here, electron donor is hydrogen sulphide (H S) and only one photosystem is involved (PS I) and the reaction centre is P .
Pigments present in bacteria are bacteriochlorophyll a, b, c, d, e and g and carotenoids. Photosynthetic bacteria are classified into three groups: . Green sulphur bacteria. Example: Chlorobacterium and Chlorobium.
Figure . : Factors affecting Photosynthesis Rate of Photosynthesis Rate of Photosynthesis Rate of Photosynthesis Light intensity CO Concentration Temperature . Water Photolysis of water provides electrons and protons for the reduction of NADP, directly. Indirect roles are stomatal movement and hydration of protoplasm.
During water stress, supply of NADPH H is affected. . Minerals Deficiency of certain minerals affect photosynthesis e.g. mineral involved in the synthesis of chlorophyll (Mg, Fe and N), Phosphorylation reactions (P), Photolysis of water (Mn and