Specimen Prep - Sexual Reproduction in Flowering Plants

Specimen Prep Guide: Sexual Reproduction in Flowering Plants

Flower Structure: Know the parts of a typical flower and their functions (sepals, petals, stamens, pistil).
Gametogenesis: Understand the processes of microsporogenesis (formation of pollen grains) and megasporogenesis (formation of the embryo sac).
Pollination: Differentiate between autogamy, geitonogamy, and xenogamy. Know the agents of pollination and the adaptations of flowers for each.
Double Fertilization: Understand the fusion of one male gamete with the egg cell (syngamy) and the other with the polar nuclei (triple fusion).
Post-Fertilization: Know the development of the endosperm and embryo, and the maturation of the ovule into a seed and the ovary into a fruit.

Problem Type: Calculating the number of meiotic and mitotic divisions required for the formation of a certain number of seeds or pollen grains.
Example: To form 100 seeds, you need 100 pollen grains and 100 embryo sacs. This requires 25 meiotic divisions for the pollen grains (since one MMC produces 4 pollen grains) and 100 meiotic divisions for the embryo sacs (since one MMC produces one functional embryo sac). Total meiotic divisions = 125.

Scenario: You are given a flower with small, inconspicuous petals, and the stamens and stigma are well-exposed. What would be the likely agent of pollination?
Analysis: The features suggest wind pollination (anemophily), as there is no need to attract insects.
Diagram Interpretation: Be able to identify the parts of a mature embryo sac (egg apparatus, polar nuclei, antipodal cells) and understand their roles in fertilization.

Discovery of Double Fertilization: This process was discovered by Nawaschin in Lilium and Fritillaria. His work was a landmark in understanding the reproductive process in angiosperms.

Assertion: Geitonogamy is functionally cross-pollination but genetically self-pollination. Reason: It involves a pollinating agent, but the pollen grains come from the same plant.
- (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.
Assertion: The endosperm in angiosperms is triploid. Reason: It is formed by the fusion of a male gamete with the two polar nuclei.
- (a) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.

A bilobed dithecous anther has 50 microspore mother cells per microsporangium. How many male gametophytes can this anther produce?
- Answer: A bilobed dithecous anther has 4 microsporangia. So, the total number of microspore mother cells is 50 x 4 = 200. Each microspore mother cell produces 4 male gametophytes (pollen grains). Therefore, the total number of male gametophytes is 200 x 4 = 800.