(a) Name the structures A to D. [4]
(b) State one similarity and one difference between the chromosome sets contained in the cells of structures E (embryo) and F (seed). [2]
(c) State the role of the micropyle before fertilization in the life cycle of the pea plant. [1]
(d) Suggest one function of the fibrous tissue in the pea pod. [1]
(e) A gardener regularly saves seed from his crop of beans for sowing in the following year. Occasionally plants were obtained which flowered but produced no seeds though they were cross-pollinated in the usual way. It was suspected that this was caused by a recessive allele which prevents seed production. With the aid of genetic diagram(s), show how sterile plants could appear in the population from two flowering parent plants. Use B and b to represent the alleles. [4]
(f) Give a reason why the gardener only occasionally finds sterile plants. [1]
ANSWERS
(a) A: Calyx or sepal; B: Pericarp/ fruit wall; C: funicle / seed stalk; D: remains of style;
(b) Similarity: Both have the same number of chromosomes (2n = 14);
Difference: F (seed coat / testa) has the same genetic materials as the parent (maternal) plant as it develops from the integuments / ovule wall of the maternal plant [1/2]
E (embryo) has only half of the genetic material that is similar to the maternal/parent plant. The other half is similar to the paternal plant. It is the result of fertilization of the male gamete and ovum;
(c) After pollination, the pollen tube releases the male gametes, which enter the embryo sac of the ovule through the micropyle;
(d) Unequal drying of the fibrous tissue in the pea pod creates tension and causes the two halves of the fruit wall/pericarp to split open and twist and turn. This scatters the seeds away from the parent plant;
(e)
(f) Chances of getting a sterile plant is 25% for each offspring, hence the gardener occasionally finds sterile plants;
No comments:
Post a Comment