Question

Student to attempt either option (A) or (B):
(A) 
(i) Write two crucial changes, the seed undergoes while reaching maturity that enable them to be in a viable state until the onset of favourable conditions. 
(ii) Name the oldest viable seed excavated from Arctic Tundra as per the records. 
OR (B) 
(i) Pea flower produced seed sets. Give reason. 
(ii) In case of Polyembryony, an embryo ‘P’ develops from a synergid and the embryo ‘Q’ develops from the nucellus. State the ploidy of embryo ‘P’ and ‘Q’.

Hint:

In polyembryony, embryos can arise from different tissues with varying ploidy levels, such as haploid gametophytic cells (synergids) or diploid sporophytic cells (nucellus).

Answer 1

(A):
Step 1: For (i), one crucial change is dehydration, where the seed loses water to enter a dormant state, preventing premature germination. Another change is the development of protective layers like the seed coat, which shields the embryo from environmental stress.
Step 2: For (ii), the oldest viable seed excavated from the Arctic Tundra is the Silene stenophylla, dated to about 32,000 years ago, which was successfully germinated.
OR
(B):
Step 1: For (i), pea flowers produce seed sets because they undergo self-pollination, as their flowers are cleistogamous (closed), ensuring pollen from the anther fertilizes the ovule within the same flower.
Step 2: For (ii), embryo ‘P’ (from synergid) is haploid (n) since synergids are part of the female gametophyte, while embryo ‘Q’ (from nucellus) is diploid (2n) as the nucellus is sporophytic tissue.