2. (a)Despite favorable climatic conditions, a farmer’s crop failed to give a good yield. Give the possible reasons for this.
(b)What is the right time to spray weedicides?

A farmer’s crop failed to give a good yield due to the following reasons.

1) Nutrients are not sufficient for the crop or nutrients are present in very high amount in the soil which causes toxicity.

2) If proper irrigation is not applied to the field.

3) If the seeds are not of good quality, the yield is also reduced.

The right time to spray weedicides are 30 to 40 days after sowing.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

weathering is the answer.