Biology Today — December 2017

4. (d) : C 4 fixation is a photosynthetic process in some plants
   such as sugarcane, corn, etc., where oxygenase activity of
   enzyme RuBisCO in photorespiration is prevented. For this
   purpose, C 4 plants utilise their specific leaf anatomy where
   chloroplasts exist in both mesophyll and bundle sheath
   cells. The mesophyll cells incorporate CO 2 in a 4-C organic
   acid which is transported back to bundle sheath cells
   where normal C 3 pathway follows. In C 4 plants, RuBisCO
   is located only in bundle sheath cells where photosynthetic
   release of oxygen does not occur. Bundle sheath cells have
   a high intracellular concentration of CO 2 due to flow of C 4
   acids and their decarboxylation to release CO 2. Hence, in
   C 4 plants RuBisCO functions purely as carboxylase, thus
   preventing photorespiration.


5. (a) : The sequence of anticodon for an amino acid is
   complementary to its mRNA sequence or codon. Therefore,
   the anticodon will be similar to the sequence of template
   strand of DNA, from which mRNA is transcribed, except
   that the thymine will be replaced by uracil so, if the triplet
   base sequence for an amino acid in DNA is TTT, its mRNA
   sequence will be AAA and the anticodon for it is UUU.


6. (d) : In gymnosperms, the endosperm is formed before
   fertilisation, hence is haploid. The integuments of ovule and
   nucellus are diploid structures while archegonia represents
   female gametophyte which is a haploid structure. So, if
   endosperm (n) has 80 chromosomes then, integument and
   nucellus (both diploid) will have 160 chromosomes and
   archegonia (n) will have 80 chromosomes.


7. (c) : Polychaetes, include annelids such as Nereis, having
   well developed paired paddle-like flap structures in each of
   their segments called parapodia. Each of these parapodia
   bear numerous bristle-like setae. While the oligochaete
   comprises of annelids having few setae as compared to
   polychaetes, e.g., earthworm. Each segment of annelid
   bears a ring of tiny, curved, chitinous structures known
   as setae, which are embedded in skin, inside a setal sac.
   From the above description of two annelids, it can be thus,
   concluded that ‘X’ can be classified as oligochaete and ‘Y’
   as polychaete.


8. (d) : Cytokinin e.g., kinetin is known to mobilise and
   accumulate nutrients into leaves and cells from other parts
   of plants. In the given experiment, only the left cotyledon
   of seedling A and right cotyledon of seedling B are treated
   with kinetin, therefore, only these two cotyledons of both
   the seedlings would show accumulation of nutrients in
   them, i.e., acts as nutrient sink. The radioactivity will be
   retained in those cotyledons in which kinetin was injected.
   This is because in seedling A, the labelled compound i.e.,
   [^14 C]^ AIBA, will move toward the cytokinin application

whereas in seedling B, since cytokinin is applied on the

marker, i.e., [^14 C]^ AIBA, no movement is observed.

9. (d) : RNA polymerase is an enzyme which synthesises
   RNA from a DNA template. The process is called transcription.


10. (a) : A cross between AabbCC and aaBbCc will be:
    AabbCC × aaBbCc

Gametes:AbC abC

AbC abC

aBC abC aBc abc

Parents:

Progeny:

aBC AaBbCC

pink flower,

tall plant,

axillary flower

aaBbCC

white flower,

tall plant,

axillary flower

abC AabbCC

pink flower,

dwarf plant,

axillary flower

aabbCC

white flower,

dwarf plant,

axillary flower

aBc AaBbCc

pink flower,

tall plant,

axillary flower

aaBbCc

white flower,

tall plant,

axillary flower

abc AabbCc

pink flower,

dwarf plant,

axillary flower

aabbCc

white flower,

dwarf plant,

axillary flower

Phenotypic ratio is:

Pink flower Pink flower White flower White flower

tall plant dwarf plant tall plant dwarf plant

axillary flowers axillary flowers axillary flowers axillary flowers

(2) (2) (2) (2)

or 2/8 : 2/8 : 2/8 : 2/8

So, the proportion of tall plant having pink and axillary

flower would be 25%.

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MPP-8 CLASS XI ANSWER KEY

1. (c) 2. (d) 3. (a) 4. (b) 5. (a)


2. (b) 7. (b) 8. (d) 9. (a) 10. (c)


3. (b) 12. (d) 13. (d) 14. (b) 15. (b)


4. (b) 17. (d) 18. (d) 19. (d) 20. (c)


5. (c) 22. (d) 23. (b) 24. (c) 25. (c)


6. (a) 27. (c) 28. (a) 29. (c) 30. (c)


7. (b) 32. (a) 33. (a) 34. (c) 35. (b)


8. (c) 37. (c) 38. (a) 39. (c) 40. (b)