Subject

Biology

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

51.

Assertion: Polytene chromosomes have a high amount of DNA.

Reason: Polytene chromosomes are formed by repeated replication of chromosomal DNA without separation of chromatids.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


A.

If both assertion and reason are true and reason is the correct explanation of assertion

Polytene chromosomes are quite common in salivary glands of insects and so are called salivary chromosomes. These chromosomes have high amount of DNA of almost I 000 times in Drosophila as compared to ordinary somatic chromosomes. These chromosomes are multistranded. They are in permanent prophase stage. These chromosomes& are formed by somatic pairing between homologous chromosomes and repeated replication pf their chromonemata without separation of chromatids. All the chromosomes may remain attached to one another at a common point called chromocentre.


52.

Assertion: The earliest organisms that appeared on the Earth were non-green and presumably anaerobes.

Reason: The first autotrophic organisms were the chemoautotrophs that never released oxygen.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


B.

If both assertion and reason are true but reason is not the correct explanation of assertion

The first living organisms originated among organic molecules and in oxygen free atmosphere. They presumably obtained energy by fermentation of some of these organic molecules. They were non-green and anaerobes (capable of respiring in absence of oxygen). They depended on the existing organic molecules for their nutrition, hence they were heterotrophs. Then came autotrophs when the supply of existing organic molecules were exhausted. These organisms were capable of producing their own organic molecules by chemosynthesis. They synthesized food from inorganic molecules. Photoautotrophs were also anaerobic at first but later on oxygen releasing photosynthetic organism developed


53.

Assertion: UV radiation causes photodissociation of ozone into O2 and O3 thus causing damage to the stratospheric ozone layer.

Reason: Ozone hole is resulting in global warming and climate change.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


A.

If both assertion and reason are true and reason is the correct explanation of assertion

Stratosphere zone of earth's atmosphere contains a layer of ozone (O3) which prevents the earth surface from about 99% of incoming solar ultraviolet radiations. The primary chemicals responsible for ozone depletion are a group of chlorine containing compounds called chloroflourocarbons (CFCs) used as coolants in refrigerators and air conditioners and propellants for aerosol cans and foam blowing agents for insulation and packaging and also as solvents. After their release into troposphere CFCs go to stratosphere when these are broken down by ultraviolet radiations releasing chlorine or bromine which break O3 molecules into O2 and O.

Due to depletion of Olayer, higher levels of ultra violet rays reach earth surface. Depletion in the concentration of ozone over a restricted area is called ozone hole. Ozone depletions results in problems like skin cancer, cataract animals becoming blind, mutations, inhibiting photosynthesis, decreases in productivity. Decreased photosynthetic activity will increase depletion of O3 layer, higher levels of ultra violet rays reach earth surface. Depletion in the concentration of ozone over a restricted area is called ozone hole. Ozone depletions results in problems like skin cancer, cataract animals becoming blind, mutations, inhibiting photosynthesis, decreases in productivity.

Decreased photosynthetic activity will increase Oconcentration of the atmosphere resulting in global warming. Besides CFCs, nitrogen oxide and hydrocarbons are also responsible for O2 depletion concentration of the atmosphere resulting in global warming. Besides CFCs, nitrogen oxide and hydrocarbons are also responsible for O3 depletion


54.

Assertion: Inflammation of a skeletal joint may immobilize the movements of the joint.

Reason: Uric acid crystals in the joint cavity and ossification of articular cartilage lead to this

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


A.

If both assertion and reason are true and reason is the correct explanation of assertion

Inflammation is a process in which the body's WBCs and the chemicals released into the blood or the affected tissue to protect us from in feetion and foreign substances such as bacteria and viruses. This releases of chemicals increases the blood flow to the area of injury or infection. Inflammation is characterized by redness, swollen joint that is warm to touch, joint pain, joint stiffness & loss of joint function. The increase number of cells and inflammatory substances within the joint causes irritation, wearing down of cartilage (cushions at the end of bones) and swelling of the joint lining. Inflammation of one or more joint results in arthritis. When there is a deposition of uric acid and crystals of sodium urates in the joints it will lead to gout arthritis. Uric acids is the end metabolism products of nitrogen containing purine nucleic acid. Gout generally affects one or two joints only. It is very painful particularly at night, and makes movement difficult. Gout generally affects great toe.


55.

Assertion: The concentration of methane in the atmosphere has more than doubled in the last 250 years.

Reason: Wetlands and rice fields are the major sources of methane.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


A.

If both assertion and reason are true and reason is the correct explanation of assertion

Hydrocarbon are major air pollutants. Methane is produced naturally during decomposition of organic matter, incomplete biomass combustion. Its concentration was 700 ppb in pre-industrial times and 1750 ppb in 2000. So the concentration has more than doubled in the last 250 years. Flooded paddy fields, marshes, cattles etc. are the major sources of this gas.


56.

Assertion: In tropical rain forests, O-horizon and A-horizon of soil profile are shallow and nutrient-poor.

Reason: Excessive growth of micro-organisms in the soil depletes its organic content.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


B.

If both assertion and reason are true but reason is not the correct explanation of assertion

A cross section of well developed soil shows more or less distinct layers called horizons.

0- horizon is the topmost layer of soil and A-horizon comes below O horizon. In the topmost layer, vegetation grows and various biological activities takes place. Tropical rain forests are found in tropical zone of the world and are characterized by very high temperature and abundance of rainfall. Soil in these area arc red latosols and are exceedingly thick. Leaching of minerals from the top soil occurs rapidly but cycling of nutrients also occur here. The laterite soils arc generally infertile because of intensive leaching and not due to growth of micro-organism.


57.

Assertion: LSD and marijuana are clinically used as analgesics.

Reason: Both these drugs suppress brain function.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


D.

If both assertion and reason are false.

An analgesic is any member of the diverse group of drugs used to relieve pain and to achieve analgesia. Analgesic drugs act in various ways on the peripheral and central nervous system; they include paracetamol (acetaminophen), the nonsteroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, narcotic drugs such as morphine, synthetic drugs with narcotic properties such as tramadol, and various others. LSD and marijuana are used as hallucinogens. Hallucinogens are natural and synthetic (synthesized) substances that, when ingested (taken into the body), significantly alter one's state of consciousness. Hallucinogenic compounds often cause people to see (or think they sec) random colours, patterns, events, and objects that do not exist. These substances are sometimes called "pyschedelic," or "mindexpanding" drugs.

Marijuana and hashish, two substances derived from the hemp plant (Cannabis sativa), are also considered natural hallucinogens. Marijuana (also called grass, pot, tea, weed, or reefer), a green herb from the flower of the hemp plant, is considered a mild hallucinogen. Hashish is marijuana in a more potent concentrated form. Both drugs arc usually smoked. Their effects include a feeling of relaxation, faster heart rate, the sensation that time is passing more slowly, and a greater sense of hearing, taste, touch. and smell.

LSD (Lysergic Acid Dicthylamiclc) is the most common hallucinogen and one of the most potent mood-changing chemicals. It is manufactured from lysergic acid, found in a fungus that grows on rye and other grains. LSD users may experience flashbacks of visions they had when on the drug. Some LSD users suffer organic brain damage, which results in impaired memory and attention span, confusion, and difficulty in thinking.


58.

Assertion: Deforestation is one main factor contributing to global warming.

Reason: Besides CO2, two other gases methane and CFCs are also included under green house gases.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


B.

If both assertion and reason are true but reason is not the correct explanation of assertion

Deforestation increases atmospheric COcontent by releasing carbon stored in organic matter and reduced primary productivity. So deforestation is one of the main factors contributing to global warming other than green house gases. The various green house gases are CO2 (60% warming effect), CH4 (20% warming effect) CFC ( 14% warming effect) and nitrogen oxide (N2O 6% warming effect). Due to increase of CO2 concentration, the absorption of heat radiation also increase thus increasing the temperature. This increase in temperature may causes melting of glacier and polar ice caps, which is called global warming. This melting of glaciers and polar ice results in raising the sea level. Actually these green house gases absorbs infra red radiations (heat) of the sun like glass and thus traps the heat and does not allow it to radiate back to the space. They instead radiate the heat back to earth, thus causing increase in temperature


59.

Assertion: An organism with lethal mutation may not even develop beyond the zygote stage.

Reason: All types of gene mutations are lethal.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


C.

If assertion is true but reason is false

 Mutations are sudden and abruptive qualitative or quantitative change in the genetic material of an organism. According to their effects on the phenotype mutations may be classified as lethals, subvitals and supcrvitals. Lethal mutations results in death of the cells or organism in which they occur. The organism may not even develop beyond the zygote stage. Subvital reduces the chances of survival. Supervital mutations results in the improvement of biological fitness under certain conditions. There may also be mutations which arc neither harmful nor beneficial to the organisms in which they occur.


60.

Assertion: Escherichia coli, Shigella sp. and Salmonella sp. are all responsible for diarrhoeal disease.

Reason: Dehydration is common to al I types of diarrhoeal diseases and adequate supply of fluids electrolytes should be ensured.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false.


B.

If both assertion and reason are true but reason is not the correct explanation of assertion

E.coli, Shigella sp, and Salmonella species arc all bacteria which arc responsible for the diarrhoea diseases. Diarrhoea is a frequent bowel evacuation or the passage of abnormally son or liquid faeces. It may be caused by intestinal infections, other form of intestinal inflammation (such as Colitis or Crohn's disease), malabsorption, anxiety and the irritable bowel syndrome.

Severe or prolonged diarrhoea may lead to excess losses of fluid, salts and nutrients in the faeces. Dehydration (whose symptoms includes great thirst, nausea and exhaustion) is common to all types of diarrhoeal diseases. The condition is treated by drinking plenty of water. severe cases require oral rehydration therapy or intravenous administration of water and salts. One litre of ORS (Oral rehydration solution) contains 1.5 gm glucose, 3.5 gm NaCl, 2.9 gm KCI & 2.9 gm trisodium citrate