Subject

Biology

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

51.

Assertion : Chlorofluorocarbons are responsible for ozone depletion.

Reason : Ozone level decreases by as much as 67% every year.

  • 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 slight thinning of ozone layer occurs naturally for a few months every year over Antarctica. It decreases by 67% every year.

The primary chemicals responsible for ozone depletion are a group of chlorine containing compounds called Chloroflurocarbons (CFCs), used as coolants in air conditioners and refrigerators and propellants for aerosol cans and form blowing agents for insulation and packaging and also as solvents.

Besides halons, methyl bromide, methyl chloroform, carbon tetrachloride and nitrous oxide are also responsible for O3 loss. After their release into troposphere, CFCs and other chlorine containing compounds go to stratosphere where these are broken down by UV-radiations releasing chlorine. Similarly, Bromine (Br) is released by breakdown of halons and methyl bromide. The sunlight catalyzes the chemical reaction by which chlorine or bromine break O3 molecules and convert them into O2 molecules. This chemical reaction does not change Cl or Br and thus single chlorine or bromine atom can breakdown many thousands of O3 molecules.


52.

Assertion : Pollution is always caused by human activities.

Reason : Pollution is not different from contamination.

  • 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

Pollution is an undesirable change in the physical, chemical or biological characteristics of air, water and land that may or will harmfully affect human lives or other organism. It is either natural or man- made. Natural pollution comes from volcanic eruptions, emission of natural gas, soil erosion, UV rays, etc. Most of the pollution is man-made.

Contamination occurs due to the presence of harmful organisms or their products or undersirable products in a desirable product causing disease or discomfort, for the organism who consume it. Therefore, pollution and contamination are two different things.


53.

Which part of the world has a high density of organism?

  • Deciduous forests

  • Grasslands

  • Tropical rain forests

  • Savannahs


C.

Tropical rain forests

Tropical rain forests are mainly found in central America, along Amazon and Orinoco rivers, South America, Congo river basin of Africa, Malagasy Republic and South east Asia including India. Diversity of life is so high that a hectare of the forest may have as many as 200 species of trees, 70% - 80% of all insects and 80- 85% of all birds are known from tropical forests. Productivity of this biome is also very high and life is abundant. It has different varieties and number of plants and animals.


54.

Assertion : Antigen can be easily recognized because it has antigenic determinants.

Reason : The recognition ability is innate.

  • 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

Antigen is any substance that may be specifically bound by an antibody molecule. These are mainly proteins but can be polysaccharides, glycoproteins or other types of conjugated proteins, nucleic acids or chemicals.

Each antigen has many antigenic determinants, also called epitopes, of the antigen. As each antibody binds with 2 or more such determinants, one antigen can bind with many antibodies. The recognition ability is innate and develops without exposure to the antigen. When the antigen first enters the body, it can bind directly to the appropriate receptors on B cells. However, a full antibody response requires that the B cells contact helper T cells. ln the case of T cells, the antigen is taken up by an antigen-presenting cells and partially digested. A peptide fragment of it is presented to the appropriate receptors on T cells. In either case, the cells are stimulated to divide, forming clones of cells that respond to this antigen.


55.

If a homozygous red-flowered plant is crossed with a homozygous white-flowered plant, the offsprings will be

  • half- white flowered

  • half- red flowered

  • all white flowered

  • all red flowered


D.

all red flowered

The red colour of flower dominates upon white colour of flower. In the present varieties both parents are of pure variety, therefore, the offsprings will be all heterozygous red flowered as shown below:

Parents                           RR                            rr

                             (Red flowered)           (White flowered)

Gametes                     R          R                 r          r

F1 generation                 Rr         Rr        Rr         Rr

(offspring)                  (Heterozygous red flowered plants)


56.

Pure line breed refers to

  • heterozygosity only

  • heterozygosity and linkage

  • homozygosity only

  • homozygosity and self assortment


C.

homozygosity only

Pure breeds are cultivated varieties or cultivars of an animal species, achieved through the process of selective breeding. Also, it is a true breeding genotypes, a line that has been rendered homozygous for all genes under consideration in successive generations, a line in which homozygous individuals produce only homozygous offspring like parents.


57.

Gene which suppresses other gene's activity but does not lie on the same locus is called as

  • epistatic

  • supplementary

  • hypostatic

  • codominant


A.

epistatic

The phenomenon by which a gene suppresses the phenotypic expression of a non- allelic gene is called epistasis. In F2 generation, the ratio for epistatic gene is 12 : 3. 

The alleles which do not show dominant recessive relationship and are able to express themselves independently when present together are called co- dominant alleles.

Supplementary genes are a pair of non- allelic genes, one of which produces its effect independently in the dominant state while the dominant allele of the second gene is without any independent effect. Although, it is able to modify the effect of the former to produce a new trait.


58.

Assertion : The earliest fossil form in the phylogeny of horse is eohippus.

Reason : Eohippus lived during the early pliocene epoch.

  • 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

The evolution of Horses include- small, terriero sized  Hydracotherium eohippus to the large modern horse, Equus eohippus, found in Eocene period.

Eohippus was the earliest known horse. It is also known as Hyracotherium. It was only 2 feet long and 8 to 9 inches high at the shoulder. It had 4 hoofed toes on front feet and 3 hoofed ant on each hind foot. It had long skull with 44 long crowned teeth. 

This horse was a herbivore that mainly ate soft leaves and plant shoots. It lived early during Eocene Epoch ie, 50 million years ago.


59.

Assertion : Vegetable oils are fats which are present in plant cells in soluble form.

Reason : Vegetable oils occur only in cells of embryo.

  • 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

Vegetable oils and fats are located in the form of small insoluble droplets within the plant cells. They are commonly found in seeds, especially in the endosperm and cotyledons. In most of the cereals, however, the fat occurs almost exclusively in the embryo. Olive and palm oils are two important examples that are obtained from the fleshy pericarp of the fruit. Less frequently, oils and fats are extracted from the roots, stems and foliage.


60.

Assertion : Haemophilia is a recessive sex linked disease.

Reason : Haemophilia occurs due to mutation of a structural gene on chromosome 15.

  • 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

Haemophilia is also known as bleeder disease. It is an example of sex linked inheritance in humans. It is either of two hereditary disorders in which the blood clots very slowly, due to a deficiency of either of two coagulation factors -

  1. Haemophilia A- It is due to deficiency of factor VIII (antihaemophilic factor)
  2. Haemophilia B- It is due to deficiency of factor IX (Christmas factor).

The patient may experience prolonged bleeding following any injury or wound, and in severe cases there is spontaneous bleeding into muscles and joints. It is controlled by a sex-linked gene, which means that it is almost exclusively restricted to males; women can carry the disease- and pass it on to their sons- without being affected themselves. The genes encoding factors VIII and IX have been used in gene therapy trials for haemophilia.

Mutations of a structural gene on chromosome 15 is the molecular basis of Marfan syndrome. It is due to dominant mutation resulting in the production of abnormal form of connective tissues and characteritic extreme looseness of joints.