krit.club logo

Biology - Flowering Plants (Morphology of Flower, Pollination, Fertilization)

Grade 9ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Flower Structure: A typical flower is a modified shoot consisting of four whorls: Calyx (Sepals), Corolla (Petals), Androecium (Stamens), and Gynoecium (Carpels/Pistil).

•

Androecium: The male reproductive part. Each stamen consists of a filament and an anther. The anther produces pollen grains which represent the male gametophyte (nn).

•

Gynoecium: The female reproductive part. Each carpel consists of a Stigma (receptive surface), Style (connective tube), and Ovary (containing ovules).

•

Pollination: The transfer of pollen grains from the anther to the stigma. Types include Autogamy (same flower), Geitonogamy (different flower, same plant), and Allogamy/Xenogamy (cross-pollination between different plants).

•

Agents of Pollination: Includes Anemophily (wind), Hydrophily (water), Entomophily (insects), and Ornithophily (birds).

•

Pollen-Pistil Interaction: Upon reaching a compatible stigma, the pollen grain germinates to form a pollen tube that carries two male gametes (nn) towards the embryo sac.

•

Double Fertilization: A characteristic of Angiosperms where one male gamete fuses with the egg to form a Zygote (2n2n), and the second male gamete fuses with the two polar nuclei (secondary nucleus) to form the Primary Endosperm Nucleus (3n3n).

•

Post-Fertilization Changes: The ovary develops into the fruit, while the ovules develop into seeds. The zygote becomes the embryo, and the PENPEN becomes the endosperm (nutritive tissue).

📐Formulae

Syngamy: Male Gamete (n)+Egg Cell (n)→Zygote (2n)\text{Syngamy: Male Gamete } (n) + \text{Egg Cell } (n) \rightarrow \text{Zygote } (2n)

Triple Fusion: Male Gamete (n)+Secondary Nucleus (2n)→PEN (3n)\text{Triple Fusion: Male Gamete } (n) + \text{Secondary Nucleus } (2n) \rightarrow \text{PEN } (3n)

Double Fertilization=Syngamy+Triple Fusion\text{Double Fertilization} = \text{Syngamy} + \text{Triple Fusion}

💡Examples

Problem 1:

If the diploid number (2n2n) of a flowering plant is 1818, determine the number of chromosomes in: (i) Pollen grain, (ii) Endosperm, (iii) Seed coat.

Solution:

(i) 99, (ii) 2727, (iii) 1818

Explanation:

Pollen grains are haploid (n=182=9n = \frac{18}{2} = 9). Endosperm is triploid (3n=3×9=273n = 3 \times 9 = 27). The seed coat develops from the integuments of the ovule, which are parental diploid tissue (2n=182n = 18).

Problem 2:

Contrast the characteristics of flowers pollinated by wind (AnemophilyAnemophily) versus those pollinated by insects (EntomophilyEntomophily).

Solution:

Wind: Light, non-sticky pollen; versatile anthers; feathery stigmas. Insects: Large, brightly colored petals; nectar production; sticky pollen grains.

Explanation:

Wind-pollinated flowers need to maximize the chance of catching airborne pollen, hence the feathery stigma. Insect-pollinated flowers must attract vectors using visual or olfactory cues.