Structure of Dicot and Monocot Seeds: Parts Compared

A seed is a mature fertilised ovule containing an embryo and stored food protected by seed coat. Dicot seeds like bean and gram have two cotyledons, while monocot seeds like maize and wheat have one cotyledon. Their internal structure differs in food storage place, embryo parts and germination pattern.

Comparing dicot and monocot seeds helps students understand plant classification, germination types and food reserves that humans use as grains and pulses for nutrition.

Key Concepts

Dicot seed example bean: Testa outer seed coat and tegmen inner, hilum scar of attachment, micropyle small pore for water entry. Embryo has two fleshy cotyledons storing food, plumule future shoot, radicle future root, axis is tigellum. No endosperm at maturity, called non-endospermic or exalbuminous. Monocot seed example maize: Fruit wall pericarp fused with seed coat. Large endosperm stores starch, outer aleurone layer rich in protein. Embryo has single shield-shaped cotyledon called scutellum absorbing food, plumule protected by coleoptile sheath, radicle by coleorhiza. Such seeds are endospermic or albuminous.

How It Works

1. In dicots double fertilisation forms endosperm initially but cotyledons absorb it completely before seed matures, becoming thick food stores.
2. In monocot maize endosperm persists and is separated from embryo by scutellum which secretes enzymes during germination to digest starch.
3. During germination water enters through micropyle in dicot or through seed coat in monocot, activating enzymes and embryo growth.

Worked Example

Weigh a soaked bean seed 1.2 g. Separate parts: seed coat 0.15 g, two cotyledons 0.85 g, embryo axis 0.20 g. Cotyledon percentage = 0.85 divided by 1.2 times 100 = 70.8 percent food storage in cotyledons. Maize grain weight 0.30 g: endosperm 0.24 g, embryo 0.04 g, pericarp plus coat 0.02 g. Endosperm percentage = 0.24 divided by 0.30 times 100 = 80 percent. Comparison shows dicot stores in cotyledons 70.8 percent, monocot stores in endosperm 80 percent, cotyledon number 2 versus 1 confirms class.

Common Misconceptions

• Misconception: Maize grain is only a seed alone. Correction: It is a fruit caryopsis where pericarp is fused with seed coat inseparably.
• Misconception: All dicot seeds lack endosperm. Correction: Castor is dicot but endospermic with thin cotyledons and large endosperm.
• Misconception: Scutellum is not a cotyledon. Correction: Scutellum is the single modified cotyledon of monocot embryo specialised for absorption.

Real-World Applications

Pulses like gram, bean and pea are protein-rich dicot seeds used as dal because cotyledons store proteins. Cereals like wheat, rice and maize are energy-rich monocot seeds because endosperm stores starch for flour. Seed testing laboratories check hilum, micropyle and embryo health for germination certification. Milling industry separates maize aleurone and endosperm fractions for oil and starch products.

Dicot seeds bear two food-storing cotyledons and usually lack endosperm at maturity, monocot seeds bear one scutellum cotyledon and retain large endosperm, seen clearly in bean versus maize structure.