Answer key

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Last edited 25 days ago by Learn LoopHQ.

Chapter: 02. The Flower

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Long Answers - Answer Key

A typical complete flower is a modified shoot attached to the stem by a stalk called the pedicel, with all floral parts attached to the upper swollen end, the thalamus. Its four whorls are: the outermost calyx, composed of small green sepals that protect the bud; the corolla, made of large, brightly coloured petals that attract pollinators; the androecium, the male reproductive whorl consisting of stamens (each with a filament and anther containing pollen grains); and the innermost gynoecium, the female reproductive whorl formed of a pistil (comprising ovary, style, and stigma, where the ovary contains ovules).

Fertilisation commences when a pollen grain lands on the stigma, absorbs moisture, and germinates to form a pollen tube. This tube grows through the style and enters the ovary, reaching an ovule. Inside the ovule, the male gamete released from the pollen tube fuses with the female gamete (egg), a process called fertilisation, resulting in the formation of a zygote. Following fertilisation, dramatic changes occur: the entire ovary develops and matures into a fruit, and the ovules inside the ovary transform into seeds. Concurrently, most other floral parts, such as sepals, petals, stamens, and the style and stigma, wither and fall off.

Flowers primarily serve as the reproductive organs of a plant, producing male and female gametes which fuse to form seeds, ensuring the continuation of the plant species. Beyond reproduction, their attractive colors, shapes, and fragrances provide significant ornamental value, used extensively for decoration and aesthetic appeal. Furthermore, flowers are a vital source of food; their ovaries develop into fruits and ovules into seeds, both consumed by humans and animals, and their nectar provides sustenance for pollinators like bees and butterflies. They also hold deep cultural and religious significance in many societies.

Seed germination is the physiological process where the dormant embryo within a seed becomes active and grows into a seedling. It commences with imbibition, the absorption of water by the seed, causing it to swell and the seed coat to rupture. Subsequently, the radicle emerges downwards to form the root system, while the plumule grows upwards, developing into the shoot system. For this process to occur successfully, three essential external conditions are required: adequate moisture (water) to activate the embryo and dissolve stored food, sufficient air (oxygen) for respiration to release energy, and an optimal warmth (temperature) range for enzyme activity and metabolic processes.

A seed, which is a fertilised ovule, primarily consists of a protective seed coat, an inactive embryo, and often an endosperm. The embryo comprises a radicle (young root), a plumule (young shoot), and cotyledons (seed leaves). Dicotyledonous seeds possess two fleshy cotyledons that store the food, typically lacking a separate endosperm, as seen in beans. In contrast, monocotyledonous seeds have only one cotyledon, which is often papery, and the food for the embryo is primarily stored in a prominent endosperm, as observed in maize.

Flowers can be classified as bisexual, possessing both male (stamens) and female (pistil) reproductive organs, such as the China rose or pea. Alternatively, they can be unisexual, having only one type of reproductive part, like the cucumber (male or female flowers separately). Based on floral whorls, flowers are complete if they contain all four whorls (calyx, corolla, androecium, gynoecium), for instance, mustard or petunia. Conversely, incomplete flowers lack one or more of these whorls, as seen in mulberry or pumpkin.

Pollination is the essential process where pollen grains are transferred from the anther to the stigma of a flower, initiating seed formation. Wind (anemophily) is one agent, facilitating transfer in flowers that are typically dull, tiny, and lack fragrance, producing abundant, light, and dry pollen that is easily caught by their large, feathery stigmas, such as in maize. Insects (entomophily) are another key agent; they pollinate flowers that are often brightly coloured, sweet-smelling, and produce nectar, with sticky pollen grains that adhere to the insect’s body and are deposited onto another flower’s sticky stigma, as seen in roses.

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