Problem 128 - Objective Biology for NEET

Question

The floral formula of fabaceae is (a) \(\oplus \oint \mathrm{K}_{(5)} \mathrm{C}_{1+2+(2)} \mathrm{A}_{(9)+1} \underline{\mathrm{G}}_{1}\) (b) \(\oplus \delta \mathrm{K}_{(5)} \mathrm{C}_{1+2-2)} \mathrm{A}_{(9)+1} \mathrm{G}_{1}\) (c) \(\oplus \oint \mathrm{K}_{(5)} \mathrm{C}_{1+2} \mathrm{~A}_{9+1} \mathrm{G}_{1}\) (d) \(\oplus \delta^{2} \mathrm{~K}_{(5)} \mathrm{C}_{1+2+2} \mathrm{~A}_{(9)-1} \mathrm{G}_{1}\)

Step-by-Step Solution

Answer

The correct floral formula for the family Fabaceae is given by option (a): \(\oplus \oint \mathrm{K}_{(5)} \mathrm{C}_{1+2+(2)} \mathrm{A}_{(9)+1} \underline{\mathrm{G}}_{1}\)

Step 1: Identify the Floral Formula Components of Fabaceae

In order to identify the elements of a floral formula, we should know that a typical floral formula is given as \(\oplus \oint \mathrm{K}_{x} \mathrm{C}_y \mathrm{A}_z \underline{\mathrm{G}}_p\), where \(\oplus\) denotes actinomorphic (radially symmetrical) flower, the \(\oint\) represents the bisexual nature of the flower. \(K\) denotes the number of sepals (calyx), \(C\) denotes the number of petals (corolla), \(A\) represents stamens, and \(G\) denotes carpels. But for family Fabaceae \(\mathrm{K}_{(5)}\) means they've got 5 sepals whorled, \(\mathrm{C}_y\) y is 1+2+(2) as they've got 1 large, two slightly smaller, and two very much smaller petals. \(\mathrm{A}_{(9)+1}\) stands to represent they've got 10 stamens in which 9 are fused together and 1 is free, and \(\underline{\mathrm{G}}_{1}\) represents a single carpel that is superior.

Step 2: Compare the Given Formulas to the Components Identified

Now, we compare these characteristics with the provided options (a) to (d). And observe that only the floral formula given in option (a) matches the typical floral formula of Fabaceae.

Key Concepts

Fabaceae family

The Fabaceae family, also known as the legume or pea family, is one of the largest and most economically significant families of flowering plants. It includes well-known plants like peas, beans, lentils, peanuts, and clover.
This family is primarily characterized by their unique trifoliate leaves and pod-like fruits, commonly known as legumes.
Fabaceae plants are pivotal in agriculture due to their ability to fix nitrogen, a process that enriches the soil by converting atmospheric nitrogen into a form that's usable by plants. This symbiosis with nitrogen-fixing bacteria not only benefits the Fabaceae plants themselves but also improves soil health for surrounding vegetation.

• Important crops in human diet: peas, beans
• Improve soil fertility through nitrogen fixation
• Known for their compound leaves and intricate flowers

Floral morphology

Understanding floral morphology helps in identifying and categorizing flowers based on their structural features. In the Fabaceae family, the unique arrangement of flower parts contributes to their distinctive look.
Key elements include the calyx, corolla, androecium, and gynoecium. In Fabaceae flowers, the calyx typically consists of five sepals that are fused together. These sepals protect the inner floral parts during bud stages.
The corolla is highly specialized, consisting of five petals in a specific arrangement:

• One large, standard petal known as the "banner"
• Two lateral petals called "wings"
• Two lower fused petals forming the "keel," which encloses the reproductive organs

This structure is not only aesthetically appealing but facilitates protection and effective pollination mechanisms.

Floral symmetry

Floral symmetry refers to how flower parts are arranged around a central axis. There are two primary types of symmetry observed in flowers: actinomorphic and zygomorphic.
Actinomorphic flowers, like daisies, can be divided into equal halves from multiple planes, showcasing radial symmetry. In contrast, zygomorphic flowers exhibit bilateral symmetry. This means that the flower can only be split into equal halves along one plane.
Fabaceae flowers are a perfect example of zygomorphic symmetry due to their distinct petal arrangement. This unique symmetry is advantageous for specialized pollination. It ensures that when pollinators like bees visit the flower, they are more effectively aligned to transfer pollen from one flower to another.

Flower structure

The intricate structure of flowers in the Fabaceae family is key to understanding their reproductive success and ecological roles. Each flower is a collection of various parts carefully designed for reproduction.
Starting with the sepals that form the outer protective layer, moving inward, we find the petals which are usually vibrant and uniquely shaped to aid in attracting pollinators.
The androecium consists of the stamens, usually ten in number for Fabaceae, with nine of them being fused together, and one remaining free. This arrangement helps in the efficient transfer of pollen.
Lastly, the gynoecium, which is represented by a single carpel in Fabaceae, is where fertilization occurs. This structure culminates in the production of fruit, typically a pod, that effectively disperses seeds. The harmony and specific arrangement of these parts are what make flowers of the Fabaceae both fascinating and functionally efficient.