a/r solution 3

Biology:

1. A

Mast cells act on body’s defence mechanism. When some allergens like different pollutants come in contact with mast cells, the allergic reaction is triggered by cross linking of IgE molecules on the surface of mast cells by allergens. Ultimately mast cells release excessive amount of inflammatory substances causing allergic reactions

2. C

In holoblastic cleavage, the cleavage furrow bisects the entire egg. In placental animals, having isolecithal and microlecithal egg, the holoblastic cleavage produces blastomeres of equal size.

Centrolecithal eggs are found in insects and in some hydrozoa. Here, yolk is concentrated at the centre of egg and the cytoplasm is present surrounding it. Meroblastic cleavage occurs in them

3. A

Any viable somatic cell of a plant has the capability to form full plant, this is known as totipotency

4. A

in a food chain the number of animals and biomass at the lower trophic level is abundant.successive links of carnivores decrease in number until there are a few carnivores at the top

5. A

Mimicry is a process by which two or more organisms independently derive protection from predation. Most common way is body colouring

Physics:

1. D

With the increase of temperature, the average energy exchanged in a collision increases and so more valence electrons can cross the energy gap, thereby increasing the electron –hole pair, so conductivity increases and resistivity decreases with temperature rise

2. A

A beetle’s movements send fast longitudinal and slow transverse waves along the sands surface. The sand scorpion intercepts the longitudinal waves first to determine direction

3. C

In a fireplace, the air above the fire gets heated up and hot air being lighter rises up. To fill the gap, cold air from the sides rushes in. thus, it feels hot ove the fire and cold in sides

4. C

The amplitude of an oscillating pendulum decreases due to air friction. As, frequency is independent of amplitude, the amplitude continues to decrease till zero while frequency remains same

5. D

As the light frequencies used in the optical fibre system is much larger than the highest frequency of microwave transmission, so, bandwidth for optical fibre is more

Chemistry:

1. C

Except nitrogen fluoride all other hydrolyse in water because, the lone pair of electron on N in NF3 is not available for ligation due to high electronegativity of F

2. D

Due to inert pair effect, lower oxidation state is more stable when we move down a group

3. B

The monoalkyl derivative first formed readily undergoes further alkylation at a still greater speed to produce polysubstituted products, and alkyl halides employed may also undergo an isomeric change. Due to these difficulties alkyl benzene is not prepared by friedel- craft’s alkylation of benzene

4. A

Grignard reagent are very reactive. Hence, the grignard reagents will react with the hydroxyl group

5. D

Cis-1,3-dihydroxycyclohexane exist in chair form as intramolecular hydrogen bonding is possible only in chair form.

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