Biology class 10th and 12th solved long answer 2024
21. What do you mean by biofertillizer? How do biofertilizers increase soil fertility?
Ans:::Biofertilizers: Biofertilizers are organisms that increase the nutrients in the soil.
The major sources of bio-fertilizers are bacteria, cyanobacteria and fungi. Soil benefits from organic fertilizers: There is always a shortage of organic matter and nitrogenous substances in Indian soil. Due to continuous leaching and growing of crops, the minerals present in the soil get reduced. Micro-organisms are helpful in removing this type of nutrient deficiency in the soil. Biofertilizers are a type of micro-organisms that increase the nutrient quality of the soil. The major sources of biofertilizers are bacteria. cyanobacteria and fungi. These bacteria have the ability to fix atmospheric free nitrogen, so that there is no shortage of nitrogen in the soil. Cyanobacteria play the role of important biofertilizers in the paddy field. Fungi establish symbiotic relationships with plants mycorrhiza. In this combination, fungal symbionts absorb phosphorus from the soil and provide it to the plants.
22. What is pest management? What do you understand by integrated pest management?
Ans ::: Pest management: Diseases, insects and weeds can cause costly and irreparable damage to livestock and crops. Methods of managing these problems include the use of insecticides or organic pest control. Integrated Pest Management (IPM) combines both methods and includes monitoring to reduce overuse of pesticide applications. The objective of IPM is to develop and expand effective, economical and environment-friendly control strategies.
Integrated Pest Management: Integrated pest management combines the use of biological, cultural and chemical practices to control pests in agricultural production. It seeks to use natural predators or parasites to control pests, using selective insecticides for backup only when insects are unable to be controlled. Natural resources. IPM should not be confused with organic practices. It does not discourage the spraying of chemicals; It promotes the spraying of selective insecticides only when the crop requires it, which usually means that
fewer pesticides are used. Describe the following:
23.
(a) DNA structure proposed by Watson and Crick (b) Meselson and Stahle experiment.
Ans. (a) DNA structure proposed by Watson and Crick: Watson and Crick also described semiconservative replication when describing the double helix structure of DNA. According to them, at the time of diploidy, both the strands get separated from each other and both the old strands act as templates to form two hybrid DNA molecules in which one strand is old and one strand remains new. According to the hypothesis of Messelson and Stahl, the two strands of DNA are not completely separated from each other at the time of diploidy. In the presence of an enzyme, both the strands are decoupled from one end or the end, then join by attracting new nucleotides towards themselves and then coiled. It is a continuous action that goes on as needed.
(b) Meselson and Stahle experiment: Matthew Stanley Messelson and Fanklim Willian Stahl in 1958 cultured E. coli bacteria in a medium containing radioactive nitrogen Ns. This allows radioactive nitrogen to reach the DNA of the bacteria. Heavy DNA (N was separated from light DNA (N) by centrifuging the mixture in the presence of CaCl. In this way both the strands of DNA were incorporated.
Now the heavy DNA molecule thus cultured was placed in a medium containing normal nitrogen (N) for diploidy. Both strands of DNA (N15) became templates after being decoupled and new strands of DNA (N) were formed. Thus in the first generation after diploidy 100% hybrid DNA was obtained (old strand of N15 and new of Nie. diploidy was semiconservative. If diploidy continues like this, 50% hybrid DNA will be obtained in the second generation, that is, in four there will be two hybrids N15 and two with simple N and in the third generation there will be two hybrid DNA, that is, two hybrids in eight and six normal.
24. Describe the lytic cycle of Bacteriophage ?
Ans::: Bacteriophage is a virus that infects a bacterial cell and reproduces inside it. They vary greatly in their size and genetic material. A bacteriophage can contain either DNA or RNA. The genes range from four to several thousand. Their capsid may be icosahedral, filamentous or head-tailed in shape. Bacteriophage life cycle: Bacteriophage exhibits two major types of life cycle:
(i) lytic cycle or viral cycle
(ii) lysogenic cycle or temperate cycle. Litic cycle: In the lytic cycle, a bacteriophage infects bacteria and kills it, releasing the progeny virus. This cycle takes place in the following phases:
(1) Adsorption: The bacteriophage attaches itself to the surface of the bacteria. This process is known as adsorption. The tips of the tail fibers are attached to specific receptors on the surface of the bacterial cell.
(ii) The tail sheath of the entry: Phase shrinks after adsorption. The base plate and tail fiber are firmly attached to the bacterial cell. Phage muramidase weakens a
