- Assertion : Sieve tube member and its adjacent companion
cells are derived from the same mother cell.
Reason : Companion cells help in maintaining proper
pressure gradient in the sieve tube elements. - Assertion : autumn wood is produced during favourable
period of the year and contains larger and wider xylem
elements.
Reason : Spring wood is produced during unfavourable
period of the year and contains smaller and narrower xylem
elements.
MOLECULAR BASIS OF INHERITANCE - Assertion : The mechanism of DNa replication is semi-
conservative.
Reason : One strand of the daughter DNa duplex is derived
from the parent while the other strand is formed anew. - Assertion : Non-template strand which does not take part
in transcription is called sense or coding strand.
Reason : Genetic code present in non-template strand is
similar to genetic code (based on mrNa) except that uracil
is replaced by thymine. - Assertion : The segment of DNa that takes part in
transcription is called transcription unit.
Reason : Transcription unit has three components i.e.,
promoter, structural gene and terminator. - Assertion : Mg2+ ion is essential for protein synthesis.
Reason : Mg2+ ion is required for the association of two
ribosomal subunits for protein synthesis to take place. - Assertion : Genetic code is non-ambiguous.
Reason : In genetic code, one codon specifies many amino
acids. - Assertion : adenine and thymine base pair is more stable
than guanine and cytosine base pair.
Reason : adenine and thymine base pair has three
hydrogen bonds whereas guanine and cytosine base pair
has two hydrogen bonds. - Assertion : DNa is acidic in nature.
Reason : DNa is composed of large number of phosphate
groups. - Assertion : Lactose is termed as inducer in lac operon.
Reason : Lactose is the substrate for enzyme b-galactosidase
and it regulates switching on and off of the operon. - Assertion : Satellite DNa forms a large portion of human
genome.
Reason : Satellite DNa sequences normally code for proteins. - Assertion : DNa is a better genetic material than rNa.
Reason : In comparison to rNa, DNa is chemically more
reactive and structurally less stable.
26. Assertion : regulator gene in lac operon is called i gene.
Reason : In lac operon regulator gene produces an inhibitor
or repressor.
27. Assertion : Semi-conservative replication of DNa was
proved by the work of Meselson and Stahl.
Reason : Double helix structure of DNa was proposed by
Watson and Crick.
28. Assertion : trNa is an adapter molecule.
Reason : The initiator trNa has the dual function of
initiation of protein synthesis as well as bringing in of first
amino acid.
29. Assertion : Some sequences in mrNa are not translated
and are referred to as untranslated regions.
Reason : untranslated regions are present at both 5’-end
(before start codon) and at 3’-end (after stop codon).
30. Assertion : Codon auG of genetic code has dual function.
Reason : Codon auG codes for methionine and it also acts
as initiation codon.
ANSWER KEY- (b) 2. (a) 3. (a) 4. (d) 5. (a)
- (d) 7. (a) 8. (c) 9. (a) 10. (b)
- (c) 12. (a) 13. (c) 14. (b) 15. (d)
- (a) 17. (a) 18. (b) 19. (a) 20. (c)
- (d) 22. (a) 23. (a) 24. (c) 25. (c)
- (a) 27. (b) 28. (b) 29. (b) 30. (a)
grace
(Grace)
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