Zoology MCQs for NEET — Practice Questions with Answers

NCERT page number-114; Anatomy; para-4

NCERT page number-114 (para-5), 115 (para-1)

NCERT page number-115; Anatomy; para-1

Urinary bladder is not lined by squamous epithelium but by transitional epithelium which is a stretchable compound epithelium. It has a single layer of cuboidal cells at the base, 2-3 middle layers of large polygonal cells and a superficial layer of large, broad rectangular cells. Stretching considerably flattens and broadens the cells of superficial and middle layers, hence causing expansion of the urinary bladder.

Mast cells are large irregular cells with granular cytoplasm, present in the areolar connective tissue. These cells store inflammation producing substances such as histamine in dense granules. Mast cells defend themselves which in turn helps in body defence by attracting phagocytes to the injured tissue.

(b) B-DNA is helical structure with 20Å and the distance between the two base pairs is 3.4Å and there are 10 base pairs in each turn or pitch (one round). Hence, one turn of the helix is approximately 34Å or 3.4 nm (10Å = 1.0 nm). Z-DNA (in comparison to B-DNA) is left handed double helical structure in which double helix winds to left in zig-zag pattern (instead of right, like B-DNA). 

(b) A competitive inhibitor competes with substrate molecule for occupying the active site of an enzyme. These inhibitors have structural resemblance with substrate molecules due to which they easily get active site of an enzyme and form an enzyme-inhibitor complex.

              E        +          I          $\to$   EI complex

       (enzyme)        (inhibitor)

(c) Total DNA (100)= A + T + C + G

                         A = 20% (given)

                         A = T (base pairing rule)

                     100 = 20+ 20 + C + G

                  C + G = 100-40 = 60

                         C = G = 30

(c) Length of one helix or the pitch per turn of helix is 34 Å in B-DNA, 25 Å in A-DNA and 46 Å in Z-model of DNA. In Z-DNA sugar molecules are seen in opposite direction. So the 3-5 diester bond forms zig-zag structure in Z-DNA.

(d) In DNA molecule the adjacent deoxyribonucleotides are joined in a chain by phosphodiester bridges or bonds, which link the 5' carbon of deoxyribose of one mononucleotide unit with 3' carbon of deoxyribose of next mononucleotide unit.

According to Watson and Crick DNA molecule consists of two such polynucleotide chains wrapped helically around each other, with the sugar phosphate chain on the outside and purine and pyrimidine on the inside of helix.

The two strands run antiparallely, i.e. one strand has phosphodiester linkage in 3'$\to$5' direction while other strand has phosphodiester linkage in 5'$\to$3' direction.

Chargaff (1950) suggested that despite wide compositional variations exhibited by different types of DNA the total amount of purines equalled the total amount of pyrimidines (A+G = T+C).