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16251.

Question : How does the Biomagnification of DDT eventually cause decline in birds' population?

Answer»

SOLUTION :DDT distrurbs calcium metabolism in birds, which causes thinning of EGG SHELL and their premature breaking. So birds. population EVENTUALLY DECLINES.
Discussion
16252.

Question : How does the administration of alpha-interferons help cancer patients?

Answer»

Solution :`ALPHA`-INTERFERONS ACTIVATES immune SYSTEM and HELPS in destroying the tumor.
Discussion
16253.

Question : How does species diversity differ from ecological diversity ?

Answer»

SOLUTION :Species DIVERSITY is the diversity at the species LEVEL while ecological diversity is at the ECOSYSTEM level diversity.
Discussion
16254.

Question : How does skin take part in excretion?

Answer»

Solution :Skin TAKES part in the excretion by ELIMINATING UREA, inorganic salts and water through SWEAT GLANDS.
Discussion
16255.

Question : How does smoking cause oxygen deficiency in the body?

Answer»

SOLUTION :Smoking INCREASES the CARBON monoxide (CO) content in blood and reduces the concentration of haembound oxygen. Thus, smoking causes oxygen DEFICIENCY in the BODY.
Discussion
16256.

Question : How does shuttle vectors differ from other types of vectors ?

Answer»

Solution :The SHUTTLE vectors are plasmids designed to replicate in cells of two different SPECIES. These vectors are created by recombinant techniques . The shuttle vectors can propagate in one host and them move into ANOTHER host any EXTRA manipulation . Most of the Eukaryotic vectors are Shuttle Vectors.
Discussion
16257.

Question : How does seasonal variation takes place on Earth ?

Answer»

Rotation on its own AXIS 
Rotation AROUND SUN 
Rotation of moon around earth
Both(A) and (B) 

ANSWER :D
Discussion
16258.

Question : How does RNA interference help in developing resistance in tobacco plant against nematode infection?

Answer»

Solution :Transgenic tobacco plant is protected against nematode/ Meloidegyne incognitia by RNA interference using AGROBACTERIUM as the vectors, nematode-specific genes were introduced into the host plant, it PRODUCES both SENSE and anti-sense RNA in the host cells, TWO RNA.s being complementary to each other formed a DOUBLE stranded (dsRNA), silenced the specific mRNA of the nematode, nematode cannot survive in tobacco plant
Discussion
16259.

Question : How does saliva act in body defence?

Answer»

SOLUTION : It CONTAINS BICARBONATE ions that neutralise the acid in food.
Discussion
16260.

Question : How does repressor protein prevent the transcription of structural genes ?

Answer»

Solution :Repressor protein binds to the OPERATOR REGION of the OPERON and prevents RNA polymerase from TRANSCRIBING the operon .
Discussion
16261.

Question : How does recycling helps to reduce pollution?

Answer»

Solution :Recycling PREVENTS the emission of many greenhouse gases which are the major cause for global warming. It also reduces the WATER pollutants and SAVE energy.
Discussion
16262.

Question : How does PS-I get supply of electrons continuously ?

Answer»

by REMOVING from photon
by removing from ferredoxin
by removing from `CO_(2)`
by removing from plastocyanin

Answer :D
Discussion
16263.

Question : How does rDNA technology help in detecting the presence of mutant gene in cancer patient.

Answer»

SOLUTION :A SINGLE STRANDED DNA or RNA, tagged with a radioactive molecule is allowed to hybridise with its complementary DNA in a CLONE of cells followed by detectin using autoradiography.
The clone having the MUTATED gene will not appear on photographic film, because probe will not be complementary with mutated gene.
Discussion
16264.

Question : How does prunninghelp in making the hedgedense ?

Answer»

It relases wound HORMONES
It induces the differentiationof new shoots from the ROOTSTOCK
It frees axillarybudsfromapicaldominace.
Theapical SHOOT growfasterafter pruing.

Answer :C
Discussion
16265.

Question : How does protocells in course oftime differentiated into cells?

Answer»

By development of cilia and flagella
By development of DOUBLE LAYERED membrane as limiting membrane
By development of CHLOROPHYLL pigments
By development of DNA-RNA system

Solution :By development of DNA-RNA system
Discussion
16266.

Question : How does pruning help in making the hedge dense?

Answer»

It RELEASES WOUND hormones
It induces the differentiation of new shoots from the ROOT stock
It frees axillarybuds from apical dominance
The apical shoot GROWS faster after pruning

Answer :C
Discussion
16267.

Question : How does plasmid differ from chromosomal DNA ?

Answer»

SOLUTION :
Discussion
16268.

Question : How does pollination is achieved in vallisneria and sea grasses

Answer»

Solution :Vallisneria are submerged FRESH water hydrophytes in which hydrophilly is observed. In vallisneria the female flower stalk is uncoiled to reach the water surface to receive the POLLEN grains carried by water currents.
In SEA GRASSES show hydrophilly TYPE of pollination here the female flowers are submerged in water to receive pollen grains for pollination inside water. pollen grains are long, ribbon like structures to be carried passively inside the water.
Discussion
16269.

Question : How does pepsinogen change into its active form ?

Answer»

It is CONVERTED into PEPSIN by hydrochloric acid
It is converted into pepsin by sodium bicarbonate
it is converted into pepsin by HYDROGEN per oxide
It is converted into pepsin by trypsin

Answer :A
Discussion
16270.

Question : How does paleontology, comparative anatomy and morphology help in study of evolution.

Answer»

Solution :Evidences that evolution of life forms has indeed taken places on earth has come from many quarters.
Paleontological evidences: Paleontology is the STUDY of fossils (Le. remains of hard parts of life forms found in rocks.)
Rocks form sediments and a cross-section of the earth. scrust depicts the arrangement of these sediments one over the other, during the long history of earth.
Sediments of different aged rocks contain fossils of different life forms that lived and died during the FORMATION of a particular segments.
Some of them appear similar to modern organism. They represent extinct organisms like dinosaurs.
The study of fossil in different sedimentary layers indicates the geological period in which they existed.
It also shows that the life forms varied over times and certain life forms are restricted to certain geological time scale.
Hence new forms of life have evolved at different time in the history of earth.
All this is called paleontology evidence.

The age of these fossils are estimated by using methods like radiocarbon dating.
Comparative Anatomy and Morphological evidences: These show the similarities and differences among the organisms of today and those that existed year ago.
These evidences come from the comparative studyof external and internal structure.
These can be determined by the following types.
Homology: It is the relation among the organ of different GROUPS of organisms, that show similarity on the basic structure and embryonic development but have different function.
Homology in organs indicates common ancestry.
It is based on divergent evolution.
When due to different needs, some structures develop differently the condition is called divergent evolution.
This result in the formation of HOMOLOGOUS organs.
Examples of homology are as follow : Thorns of Bougainvillea and tendrils of Cucurbita.

Forelimbs of animals like - whales, bats, cheetah and mammals. (eg. Humans).
Vertebrate heart and brains.
Analogy: It is a situation exactly opposite to the homology.
In analogy, the organs are functionally similar but anatomically different.
CONVERGENT evolution is the evolution where different structures evolve for the same function and hence have similarity.
This results in analogous organs.
Examples are as follow : Wings of butterfly and birds.
Eyes of octopus and mammals.
Flippers of penguins and dolphins.
Sweet potato (root modification) and potato (stem modification).
Discussion
16271.

Question : How does one visualise DNA on an agarose gel ?

Answer»

SOLUTION :A compound called ETHIDIUM Bromide stains DNA, which on irradiating with Ultraviolet LIGHT (UV light) produces orange FLUORESCENCE. Hence, DNA fragments appear as orange band in the presence of Ethidium Bromide and UV light.
Discussion
16272.

Question : How does our bodyovercom altitudesickness ?

Answer»

SOLUTION :The bodycompensates LOW OXYGEN availabilityby increasing BLOOD cell production .
The bodycompensatesdecreasingbindingcapacityof hemoglobin withoxygen byincreasing RATEOF breating .
Discussion
16273.

Question : How does one visualise DNA on agarose gel?

Answer»

Solution :On AGAROSE GEL, DNA SEGMENTS appear as fluorescent bands of orange COLOUR because they are stained with Ethidium bromide stain and irradiated with UV radiation.
Discussion
16274.

Question : How does Neanderthal man differ from the modern man in appearance ?

Answer»

Solution :Neanderthal man differ from the modern HUMAN in having semierect posture, flat cranium, SLOPING forehead, THIN large orbits, heavy brow RIDGES, protrudingjaws and no chin.
Discussion
16275.

Question : How does Mutation theory of Dev. Vries differ from Lamarck and Darwin's view in the origin of new species.

Answer»

Solution :ACCORDING to de VRIES, sudden and large variations were responsible for the origin of new SPECIES, WHEREAS Lamarck and Darwin believed in GRADUAL accumulation of all variations the causative factors in the origin of new species
Discussion
16276.

Question : How does mutation theory of De vries differ from lamarck and Darwins view in the origin of new species.

Answer»

Solution :According to de Vries, suden and large variations were RESPONSIBLE for the ORIGIN of new species, whereas Lamarck and DARWIN believed in GRADUAL accumulation of all variations as the causative FACTORS in the origin of new species.
Discussion
16277.

Question : How does inheritance of one Gene take place ?

Answer»

Solution : Inheritance of one gene can be STUDIED by hybridisation experiment carried out by Mendel where he crossed tall and dwarf pea plants to study the inheritance of one gene.
= He collected the seeds produced as a result of Petal this cross and grew them to generate plants of -Stigma the first hybrid generation.
= This generation is ALSO called the `"filial"_1` progeny or the `F_1`
=Mendel observed that all the F, progeny plants were tall like one of its parents, none were dwarf.
=He made similar observations for the other pairs of traits - he found that the F always resembled either one of the parents and that Transfer Pollen the trait of the other parent was not seen in them.
=Mendel then self - pollinated the tall `F_1` plants and to his surprise found that in the `"filial"_1` generation some of the offspring were dwarf the character that was not seen in the `F_1` generation was now expressed.
=The proportion of plants that were dwarf were 1/`4^(th)` of the `F_2` plants while 3/`4^(th)` of the `F_2` plants were tall.
=The tall and dwarf traits were identical to their parental type and did not show any blending that is all the offspring were either tall or dwarf none were of in between height.
=Similar results were OBTAINED with the other traits that he studied. Only one of the parental traits was expressed in the `F_1` generation while at the `F_2`stage both the traits were expressed in the proportion 3:1.
=The contrasting traits did not show any blending at either `F_1or F_2`, stage.
=Based on these observations, Mendel proposed that something was being stably passed down unchanged from parent to offspring through the gametes, over successive generations.
=He called these things as .factors.
=Now they are called as genes.
=Genes are the units of inheritance.
=They contain the information that is required to express a particular trait in an organism.
=Genes which CODE for a pair of contrasting traits are known as alleles i.e. they are slightly different forms of the same gene.
Discussion
16278.

Question : How does fragmentation of large habitats due to human activities lead to population decline?

Answer»

SOLUTION :LOSS of lhabitat.
Discussion
16279.

Question : How does excessive eating of salt and facts make one susceptible to heart disease?

Answer»

Solution :1. Excessive salt CONSUMPTION raises the blood pressure. It causes rise in some hormones like ADH causing IMBALANCE in the HOMEOSTASIS.
2. High blood pressure or hypertension causes pressure on heart.
3. Excessive consumption of fats LEADS to deposition of fats in the linings of major blood vessels. This leads to the FORMATION of atherosclerotic plaques, decreasing the size of the lumen of blood vessels. This condition called atherosclerosis which causes more hypertension.
4. Both these conditions, i.e. hypertension and atherosclerosis contribute to the heart disease.
Discussion
16280.

Question : How does ds RNA gain entry into eukaryotic cell to cause RNA interference?

Answer»

Solution :dsRNA gain ENTRY into eukaryotic cell either through infection by virus having RNA genome.
Mobile genetic elecmetns (TRANSPOSONS) that REPLICATE via an RNA intermediate
Discussion
16281.

Question : How does eurythermal organism enhace the overall fitness of the species?

Answer»

Solution :Many SPECIES would have evolved a relatively constant internal body temperature that permits all BIOCHEMICAL reactions and physical functions to proceed with maximal EFFICIENCY and thus the eurythermal organism enhances over all FITNESS.
Discussion
16282.

Question : How dose Drosophila show complete linkage?

Answer»

SOLUTION :C. B. Bridges DISCOVERED that crossing over is completely absent in some species of male DROSOPHILA. THEREFORE they exhibit COMPLETE linkage.
Discussion
16283.

Question : How does deforestation occur?

Answer»

Solution :1. CONVERSION of forest to agricultural LAND.
2. Trees are axed for timber to for making furniture, plywood, paper and FIRE WOOD.
Discussion
16284.

Question : How does cleavage in mammals differ from cleavage in frogs?

Answer»

Control involving the embryo's genome
Formation of TIGHT junctions
Slower RATE of CELL divisons
all of these

Answer :d
Discussion
16285.

Question :How does colostrum provide initial proteetioh against diseases to new born infants? Give one reason

Answer»

Solution :Colostrum provides PROTECTION to new born babies due to the PRESENCE of IGA ANTIBODIES essential to develop resistance
Discussion
16286.

Question : How does Cu-T acts as an effective contraceptive for human females?

Answer»

Solution :Cu-Tis an ideal contraceptive device for human females because:
Cu.ions released suppress SPERM motility and fertilising CAPACITY of sperms.
It increases PHAGOCYTOSIS of sperms within the UTERUS.
Discussion
16287.

Question : How does bacterial DNA is protected against restriction enzymes?

Answer»

SOLUTION :BACTERIA have METHYLATED RESTRICTION SITES.
Discussion
16288.

Question : How does an orchid ophrys ensures its pollination by bees?

Answer»

SOLUTION :The PLANT, Ophrys an orchid, the fiower LOOKS like a female insect to attract the male insect to GET pollinated by the male insect and it 1S otherwise called .floral mimicry ..
Discussion
16289.

Question :How does antigen-determinant differ from antigen binding site?

Answer»

By its structur
By its location
By its function
All of these

Solution :All of these
Discussion
16290.

Question : How does an electrostatic precipitator work ?

Answer»

Solution :Electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a CORONA that releases electrons.
These electrons attach to dust particles giving them a net NEGATIVE charge. The collecting PLATES are grounded and attract the CHARGED dust particles. The velocity of air between the plates must be LOW enough to allow the dust to fall.
Discussion
16291.

Question : How does Agrobacterium tumifaciens act as a suitable vector in the biotechnological experiments ? Site an example where it has been successfully used as a vector.

Answer»

SOLUTION :See Q. 23, Set-I., OUTSIDE DELHI- 2008 and See Q. 13, Set-III., Delhi Board-2011.
Discussion
16292.

Question : How does AIDS spread ?

Answer»

Solution :Due to copulation (same sex or other sex) with AIDS patient.
By HIV contaminated blood transfusion.
Due to diseased organ transplantation.
Due to use of HIV infected needlc.
From infected mother to her CHILDREN through PLACENTA and the infant who is on feeding
By DIRECT contact of the PATIENTS, or use of utensils and clothes the disease does not spread.
Discussion
16293.

Question : How does a sperm penetrate through the zona pellusida in human ovum?

Answer»

Solution :By RELEASING a SPERM lysin, ZONA lysin or acrosin which DIGEST this layer
Discussion
16294.

Question : How does a restriction nuclease function ? Explain.

Answer»

SOLUTION :SEE Q.26 (a), Set-I, DELHI BOARD 2010
Discussion
16295.

Question : How does a probe help molecular diagnosis.

Answer»


Answer :a single straded DNA/RNA tagged with a radioactive moleculear PROBE is allowed to hybridise to its comlementary DNA in a clone of cells.it followed by detection using AUTOGRAPHY. The clone having the mutated GEN will not APPEAR on the photographic flim.
Discussion
16296.

Question : How doesa scrubber function ?

Answer»

Solution :Scrubbers are generally employed in removinggaseouspollution. In a scrubber , theexhaust is PASSED through a spray of wateror lime . Waterdissolved gases and line REACTSWITH SULPHUR DIOXIDE to forma precipitate of calcium SULPHATE or sulphide .
Discussion
16297.

Question : How does a parasite affect the host?

Answer»

Solution :1. Parasite reduces the survival, growth and reproduction of the host
2. Parasite reduces the POPULATION density of host
3. They MIGHT render the host more vulnerale to predation by making it physically weak.
Discussion
16298.

Question : How does a meiocyte develop into the female gametophyte in an angiosperm? Draw a labelled diagram of the structure bearing the female gametophyte in an angiosperm and label the nutritive and the protective layer present in it.

Answer»

Solution : Megaspore mother CELL(meiocyte) undergoes meiosis producing one FUNCTIONAL megaspore, the functional megaspore divides mitotically to produce two nuclei which move to opposite POLES, each nucleus now divides twice to form four nuclei at each pole of which one nucleus from each pole moves to the centre forming two polar nuclei, walls are formed around six nuclei forming three antipodals at chalazal end, and a three celled egg apparatus (having one egg and two synergids) at the MICROPYLAR end, the polar nuclei are present in the large CENTRAL cell
Discussion
16299.

Question : How does a normal plant show resistance to insect and pest?

Answer»

Solution :Insect and pest RESISTANCE may due to morphological, biochemical or physiological CHARACTERS:
1. Hairy leaves resistant to insect pest
2. Solid stem in WHEAT -non-preference by stem sawfly
3. Smooth LEAVED and nectar less cotton varieties-do not attrect bollworms
4. High aspartic acid, Low nitrogen and Low sugar in maize-resistant to maize stem bores.
Discussion
16300.

Question : How does a mutagen induce mutation ? Explain with example.

Answer»

Solution :A mutagen is a physical or chemical agent that changes the genetic material, usually DNA. Different mutagens act on the DNA differently.
= Powerful mutagens MAY result in chromosomal instability, causing chromosomal breakages and rearrangement of the chromosomes such as translocation, deletion, and inversion. Ionizing radiations such as X-RAYS, gamma rays and alpha particles may cause DNA breakage and other damages.
= Ultraviolet radiations with WAVELENGTH above 260 nm are absorbed strongly by bases, producing pyrimidine dimers. RADIOACTIVE decay, such as 14C in DNA which decays into nitrogen.
Discussion