Fruit and Seed — Explained

Detailed Explanation

The reproductive success of angiosperms, or flowering plants, hinges significantly on the development and function of fruits and seeds. These structures are not merely containers; they represent sophisticated evolutionary adaptations for protection, nourishment, and dispersal of the next generation.

Conceptual Foundation: The Journey from Flower to Fruit and Seed

At the heart of fruit and seed formation lies the process of sexual reproduction within the flower. Following successful pollination, where pollen grains land on the stigma, and subsequent fertilization, where a male gamete fuses with the egg cell, the floral parts undergo profound changes.

The ovary, which houses the ovules, matures into the fruit, while the ovules themselves develop into seeds. This coordinated transformation ensures that the delicate embryo within the seed is protected and provided with resources for its initial growth.

The Fruit: A Protective and Dispersal Unit

Definition and Development: A fruit is essentially the ripened ovary of a flower, typically developing after fertilization. Its primary roles are to protect the immature seeds and facilitate their dispersal. In some cases, fruits can develop without fertilization, a phenomenon known as *parthenocarpy*, resulting in seedless fruits (e.g., banana, seedless grapes).

Structure of a Fruit: The fruit wall, derived from the ovary wall, is called the *pericarp*. The pericarp can be dry or fleshy and is often differentiated into three distinct layers:

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*Epicarp*: The outermost layer, forming the skin or rind of the fruit. It provides protection.
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*Mesocarp*: The middle layer, which is often fleshy and edible (e.g., mango, peach) or fibrous (e.g., coconut) or dry.
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*Endocarp*: The innermost layer, which directly encloses the seed(s). It can be thin and papery (e.g., pea), stony (e.g., mango, coconut), or membranous.

Types of Fruits: Fruits are broadly classified based on their origin from the flower:

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Simple Fruits: — These develop from a single ovary of a single flower. They can be further divided into:

* Fleshy Fruits: The pericarp is fleshy and juicy. * *Drupe*: Develops from a monocarpellary superior ovary and is one-seeded. The pericarp is differentiated into a thin epicarp, a fleshy mesocarp, and a stony endocarp (e.

g., mango, coconut, peach, plum). In coconut, the mesocarp is fibrous. * *Berry*: Develops from a monocarpellary or multicarpellary, syncarpous ovary. The epicarp is thin, and the mesocarp and endocarp are fused to form a fleshy pulp with many seeds (e.

g., tomato, grape, brinjal, guava). * *Pepo*: A type of berry with a hard, leathery rind (epicarp) formed from an inferior ovary (e.g., cucumber, pumpkin, watermelon). * *Hesperidium*: A type of berry with a leathery rind containing oil glands (epicarp and mesocarp fused) and juicy placental hairs (endocarp) (e.

g., orange, lemon). * *Pome*: A 'false fruit' where the fleshy part is the thalamus, and the true fruit (ovary) is enclosed within it (e.g., apple, pear). * Dry Fruits: The pericarp is dry and often hard.

* *Dehiscent Fruits* (splitting open at maturity to release seeds): * *Legume*: Develops from a monocarpellary superior ovary, dehisces along both dorsal and ventral sutures (e.g., pea, bean).

* *Follicle*: Dehisces along one suture only (e.g., *Delphinium*, *Calotropis*). * *Siliqua*: Develops from a bicarpellary superior ovary, dehisces from base to apex, leaving a false septum (*replum*) (e.

g., mustard, radish). * *Capsule*: Develops from a multicarpellary syncarpous ovary, dehisces in various ways (e.g., cotton, *Datura*, poppy). * *Indehiscent Fruits* (do not split open at maturity; seeds remain enclosed): * *Achene*: Small, one-seeded fruit, pericarp free from seed coat (e.

g., *Mirabilis*, sunflower). * *Caryopsis*: Small, one-seeded fruit, pericarp fused with seed coat (e.g., maize, wheat, rice). * *Nut*: One-seeded, hard, woody pericarp (e.g., cashew nut, chestnut).

* *Samara*: Winged achene, pericarp forms a wing for dispersal (e.g., elm, maple). * *Cypsela*: Achene-like fruit with persistent pappus (e.g., sunflower).

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Aggregate Fruits: — Develop from multiple separate carpels (apocarpous ovary) of a single flower. Each carpel develops into a fruitlet, and all fruitlets together form an aggregate fruit (e.g., custard apple, blackberry, raspberry, strawberry – where the fleshy part is thalamus, making it a false fruit).

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Multiple (Composite) Fruits: — Develop from the entire inflorescence, where all the flowers and their ovaries, along with the floral axis, fuse to form a single fruit (e.g., pineapple, jackfruit, mulberry).

The Seed: The Embryo's Cradle

Definition and Development: A seed is a fertilized and mature ovule. It is the reproductive unit of angiosperms, containing an embryo, stored food, and a protective seed coat. The ovule's integuments develop into the seed coat.

Structure of a Seed: A typical seed comprises:

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*Seed Coat*: The protective outer covering, derived from the integuments of the ovule. It has two layers: the outer *testa* and the inner *tegmen*. On the seed coat, a scar called the *hilum* marks the point of attachment to the fruit. Above the hilum is a small pore called the *micropyle*, which facilitates water absorption and gas exchange during germination.
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*Embryo*: The miniature plant, consisting of an *embryonal axis* and one or two *cotyledons*.

* Embryonal Axis: Comprises the *plumule* (future shoot) at the upper end and the *radicle* (future root) at the lower end. The region between the plumule and cotyledonary attachment is the *epicotyl*, and the region between the radicle and cotyledonary attachment is the *hypocotyl*. * Cotyledons: Seed leaves that store food (in exalbuminous seeds) or absorb food from the endosperm (in albuminous seeds).

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*Endosperm*: A nutritive tissue formed during double fertilization (fusion of a male gamete with the central cell). It provides nourishment to the developing embryo. In some seeds (e.g., castor, maize), it persists at maturity (*albuminous seeds*), while in others (e.g., pea, bean, groundnut), it is completely consumed by the developing embryo, and food is stored in cotyledons (*exalbuminous seeds*).

Types of Seeds:

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Dicotyledonous Seed (Dicot Seed): — Possesses two cotyledons (e.g., pea, gram, bean, groundnut). Most dicot seeds are exalbuminous. The embryo is typically curved or folded.

* Example: Pea seed. It has a thick seed coat. The hilum is visible. The embryo consists of a large embryonal axis and two large cotyledons. The plumule and radicle are distinct.

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Monocotyledonous Seed (Monocot Seed): — Possesses a single cotyledon (e.g., maize, wheat, rice, onion). Most monocot seeds are albuminous.

* Example: Maize grain (which is technically a fruit, a caryopsis, where the pericarp is fused with the seed coat). It has a large endosperm. The single cotyledon is called *scutellum*, which is shield-shaped and located to one side of the embryonal axis. The embryonal axis has a *plumule* and *radicle*, enclosed in protective sheaths called *coleoptile* and *coleorhiza*, respectively.

Seed Dormancy: A state of suspended growth and metabolism in a seed, even under favorable environmental conditions. It is an adaptive mechanism that prevents premature germination and ensures germination occurs at the most opportune time for seedling survival. Dormancy can be broken by various factors like chilling (stratification), light, or chemical treatments (e.g., gibberellins).

Seed Dispersal: The movement or transport of seeds away from the parent plant. This is crucial to reduce competition, colonize new areas, and prevent pathogen accumulation. Mechanisms include wind (anemochory, e.g., dandelion, maple), water (hydrochory, e.g., coconut), animals (zoochory, e.g., fleshy fruits eaten by birds/mammals, burrs clinging to fur), and self-dispersal (autochory, e.g., pea pods bursting).

Common Misconceptions and NEET-Specific Angle

Fruit vs. Vegetable: — Biologically, a fruit develops from the ovary and contains seeds. Vegetables are other edible plant parts (roots, stems, leaves, flowers). Tomatoes, cucumbers, and bell peppers are botanically fruits, though culinarily often treated as vegetables.
True vs. False Fruits: — Understanding the contribution of floral parts other than the ovary is key. Apple (thalamus), strawberry (thalamus), cashew (pedicel) are common NEET examples of false fruits.
Albuminous vs. Exalbuminous Seeds: — Remember that 'albuminous' means endosperm is present at maturity, while 'exalbuminous' means it's consumed, and cotyledons store food. This is a frequent point of confusion.
Monocot vs. Dicot Seed Structure: — Pay close attention to the number of cotyledons, the presence/absence of endosperm, and specific structures like scutellum, coleoptile, and coleorhiza in monocots.
Parthenocarpy vs. Apomixis: — Parthenocarpy is fruit formation without fertilization (seedless fruit). Apomixis is seed formation without fertilization (asexual seed). Both are important for NEET.

NEET questions often test specific examples of fruit types, the layers of the pericarp, the parts of a seed, and the differences between monocot and dicot seeds. Diagrams are frequently used to identify parts. Knowledge of seed dormancy and dispersal mechanisms is also tested.