11th Class

A most complex tissue in the body, composed of densely packed interconnected nerve cells called neurons (as many as \[{{10}^{10}}\] in the human brain). It specialized in communication between the various parts of the body and in integration of their activities. Nervous tissue is ectodermal (from neural plate) in origin. It forms the nervous system of the body which controls and coordinates the body functions. There is no intercellular matrix between neurons. These have permanently lost the power of division as have no centriole and have minimum power of regeneration. So these cannot be cultured in vitro. Irritability is the main function of nervous tissue. Composition of nervous tissue : Nervous tissue is formed of four types of cells : (1) Neurons (nerve cells)              (2) Neuroglia (3) Ependymal cells                         (4) Neuro-secretory cells Neurons A neuron is a nerve cell with all its branches. Neuron is formed from neuroblast. It is more...

It provide support and surface for attachment of muscle. Skeletal connective tissue form the frame work of body. It provide rigidity to body. These protect the various organ and help in locomotion. It is of three types : Cartilage, Bones, Notochord. Cartilage Cartilage is a solid but semi-rigid and flexible connective tissue. Cartilage is a nonvascular connective tissue, consisting of cells embeded in a resilent matrix of chondrin. Chondrin is a protein of cartilage. Regeneration of cartilage can occur from its peri-chondrium. Cartilage is said to be metabolically nearly inactive. In kids the cartilage cells show 2 types of growth. (1) Appositional or Perichondral or Secondary or Exogenous growth : It is due to deposition of matrix and division of chondrogenic cells of periphery. It leads to growth in thickness. (2) Endogenous or Interstitial growth : It is due to deposition of matrix and division in inner cells of cartilage. more...

It is a mobile connective tissue derived from mesoderm which consists of fibre-free fluid matrix and specialised living cells that are not formed in situ, can neither divide nor secrete matrix. Vascular tissue regularly circulates in the body, takes part in transport of material and performs such activities as scavenging healing of wounds and defence against pathogens. Vascular tissue is of two types, blood and lymph, Blood In chordates, and in annelids amongst the non chordates, the blood is a red and opaque fluid of salty taste and peculiar smell. It is a little heavier than water. The study of blood is called haematology. It is red coloured liquid connective tissue which originates from the mesoderm. It reaches into the various organs through the blood vessels and transports various chemical substances between different tissues. During embryonic state, the blood is mainly formed in the liver but little blood is also more...

Like green plants, some purple and green sulphur bacteria are capable of synthesizing their organic food in presence of light and in absence of \[{{O}_{2}},\]which is known as bacterial photosynthesis. Van Niel was the first to point out these similarities. Oxygen is not liberated in bacteria during process of photosynthesis. Their photosynthesis is non-oxygenic. Because bacteria use \[{{H}_{2}}S\]in place of water \[({{H}_{2}}O)\] as hydrogen donor. Photosynthetic bacteria are anaerobic. Only one type of pigment system (PSI) is found in bacteria except cyanobacteria which possess both PSI and PSII. Bacteria has two type of photosynthetic pigments. Bacteriochlorophyll and Bacterioviridin. The photosynthetic bacteria fall under three categories (1) Green sulphur bacteria : It contains chlorobium chlorophyll, which absorb 720-750nm (far red light) of wavelength of light. e.g., Chlorobium. (2) Purple sulphur bacteria : e.g., Chromatium. (3) Purple non-sulphur bacteria : e.g., Rhodospirillum, Rhodopseudomonas. Characteristics of bacterial photosynthesis are : (1) No definite more...

Some forms of bacteria obtain energy by chemosynthesis. This process of carbohydrate formation in which organisms use chemical reactions to obtain energy from inorganic compounds is called chemosynthesis. Such chemoautotrophic bacteria do not require light and synthesize all organic cell requirements from \[C{{O}_{2}}\] and \[{{H}_{2}}O\] and salts at the expense of oxidation of inorganic substances like (\[{{H}_{2}},N{{O}_{3}}^{},S{{O}_{4}}\]or carbonate). Some examples of chemosynthesis are : (1) Nitrifying bacteria : e.g., Nitrosomonas, Nitrosococcus, Nitrobacter etc. (2) Sulphur bacteria : e.g., Beggiatoa, Thiothrix and Thiobacillus. (3) Iron bacteria : e.g., Ferrobacillus, Leptothrix and Cladothrix. (4) Hydrogen bacteria : e.g., Bacillus pentotrophus (5) Carbon bacteria : e.g., Carboxydomonas, Bacillus oligocarbophilus.

Blackmann's law of limiting factors F.F. Blackmann (1905) proposed the law of limiting factors according to which 'when process is conditioned to its rapidity by a number of factors, the rate of process is limited by the pace of the slowest factor'.  is usually a limiting factor in photosynthesis under field conditions particularly on clear summer days under adequate water supply. Blackmann's law of limiting factor is modification of Liebig's law of minimum, which states that rate of process controlled by several factors is only as rapid as the slowest factor permits. Theory of three cardinal points was given by Sachs in 1860. According to this concept, there is minimum, optimum and maximum for each factor. For every factor, there is a minimum value when photosynthesis starts, an optimum value showing highest rate and a maximum value, above which photosynthesis fails to take place. Factors : The rate of photosynthetic more...

Before seventeenth century it was considered that plants take their food from the soil.

• Van Helmont (1648) concluded that all food of the plant is derived from water and not from soil.
• Stephen Hales (Father of Plant Physiology) (1727) reported that plants obtain a part of their nutrition from air and light may also play a role in this process.
• Joseph Priestley (1772) demonstrated that green plants (mint plant) purify the foul air (i.e., Phlogiston), produced by burning of candle, and convert it into pure air (i.e., Dephlogiston).
• Jan Ingen-Housz (1779) concluded by his experiment that purification of air was done by green parts of plant only and that too in the presence of sunlight. Green leaves and stalks liberate dephlogisticated air (Having \[{{O}_{2}}\]) during sunlight and phlogisticated air (Having \[C{{O}_{2}}\]) during dark.
• Jean Senebier (1782) proved that plants absorb \[C{{O}_{2}}\]and release more...

On the basis of discovery of Nicolas de Saussure that "The amount of \[{{O}_{2}}\] released from plants is equal to the amount of \[C{{O}_{2}}\] absorbed by plants", it was considered that \[{{O}_{2}}\] released in photosynthesis comes from \[C{{O}_{2}},\] but Ruben proved that this concept is wrong. In 1930, C.B. Van Niel proved that, sulphur bacteria use \[{{H}_{2}}S\](in place of water) and \[C{{O}_{2}}\] to synthesize carbohydrates as follows: \[6C{{O}_{2}}+12{{H}_{2}}S\xrightarrow{\,\,\,\,}{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+12S\] This led Van Niel to the postulation that in green plants, water \[({{H}_{2}}O)\] is utilized in place of \[{{H}_{2}}S\] and \[{{O}_{2}}\] is evolved in place of sulphur (S). He indicated that water is electron donar in photosynthesis. \[6C{{O}_{2}}+12{{H}_{2}}O\xrightarrow{\,\,\,\,}{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+6{{O}_{2}}\] This was confirmed by Ruben and Kamen in 1941 using Chlorella a green alga. They used isotopes of oxygen in water, i.e., \[{{H}_{2}}^{18}O\] instead of \[{{H}_{2}}O\] (normal) and noticed that liberated oxygen contains \[^{18}O\] of water and not of \[C{{O}_{2}}.\] The overall reaction can more...

Photosynthesis is an oxidation reduction process in which water is oxidised to release O2 and CO2 is reduced to form starch and sugars. Scientists have shown that photosynthesis is completed in two phases. (1) Light phase or Photochemical reactions or Light dependent reactions or Hill's reactions : During this stage energy from sunlight is absorbed and converted to chemical energy which is stored in ATP and \[NADPH+{{H}^{+}}.\] (2) Dark phase or Chemical dark reactions or Light independent reactions or Blackman reaction or Biosynthetic phase : During this stage carbohydrates are synthesized from carbon dioxide using the energy stored in the ATP and NADPH formed in the light dependent reactions. Evidence for light and dark reactions in photosynthesis : (1) Physical separation of chloroplast into grana and stroma fractions : It is now possible to separate grana and stroma fractions of chloroplast. If light is given to grana fraction in presence more...

Decker and Tio (1959) reported that light induces oxidation of photosynthetic intermediates with the help of oxygen in tobacco. It is called as photorespiration. The photorespiration is defined by Krotkov (1963) as an extra input of \[{{O}_{2}}\] and extra release of \[C{{O}_{2}}\] by green plants is light. Photorespiration is the uptake of \[{{O}_{2}}\] and release of \[C{{O}_{2}}\] in light and results from the biosynthesis of glycolate in chloroplasts and subsequent metabolism of glycolate acid in the same leaf cell. Biochemical mechanism for photorespiration is also called glycolate metabolism. Loss of energy occurs during this process. The process of photorespiration involves the involvement of chloroplasts, peroxisomes and mitochondria. RuBP carboxylase also catalyses another reaction which interferes with the successful functioning of Calvin cycle.     Biochemical mechanism (1) Ribulose-1, 5-biphosphate \[\xrightarrow{{{O}_{2}}}\] 2 Phoshoglycolic acid + 3 Phoshoglyceric more...