Monocot vs. Dicot Seed-Definition, Structure, 10 Differences, Examples

Monocot vs. Dicot Seed Overview

Definition of Monocot Seed

Seeds with a single embryonic leaf, or cotyledon, are known as monocot seeds.

  • The most crucial traits that enable the distinction of monocots and dicots are the seed structure and the number of cotyledons found in a seed.
  • The majority of monocots have trimerous (exist in three pieces) seed pods because the carpel used for fertilisation likewise has three sections.
  • A monocot seed often has a bigger size because it has a large endosperm. To sustain the embryo, a significant quantity of food is stored in the endosperm. Because they include endosperm, monocot seeds are sometimes known as albuminous seeds.
  • Although the size and form of the seeds might vary, monocot seeds often lack the symmetry of dicot seeds since they only have one cotyledon.
  • Monocot seeds often have elliptical, triangular, or egg-shaped forms.
  • Ovules turn into seeds after fertilisation; hence the ovule’s form ultimately determines how the seed will look.
  • The most significant component of a seed is the embryo, which is provided with food and nutrients by the endosperm and is externally protected by a covering.
  • The monocots represent a monophyletic group since their evolutionary history can be followed back to a sole ancestor.

Definition of Dicot Seed

  • Dicot seeds are described as having two cotyledons, or embryonic leaves, inside them.
  • Dicot seeds have two cotyledons around a single embryo with an embryo axis. Initially, dicots were used to describe all angiosperms, or blooming plants.
  • Because dicot seed pods may contain any number of chambers, they vary in size, shape, and quantity. Typically, dicot seed pods contain more seeds than monocot seed pods.
  • Frequently, dicot seeds are symmetrical and may be divided into two similar halves.
  • Dicots often have less endosperm, and in certain circumstances, it may not even exist at all.
  • The shape of the seed varies between species and may be utilized to differentiate them, similar to how peas and beans could be differentiated based on the structure of their seeds.
  • Dicot plants include a wide variety of plants, from woody trees to shrubs, and their seeds come in a wide range of sizes.
  • Dicot seeds may be further distinguished from other seeds based on whether or not the embryo is surrounded by extra sheaths.
  • Dicots are not a monophyletic group since their plants may be traced to several ancestors.

Structure of Monocot and Dicot Seeds

The following components may be used to characterise the structure of monocot and dicot seeds:

  1. Seed Coat

The seed coat covers the outermost coating of the seed, and in rare situations, it may stay bonded to the fruit wall.

The seed coat consists of two integuments, or layers of cells, located on the outside of the ovule. The tissue is harvested from the parent plant, where the tegmen and testa are formed by the inner and outer layers, respectively.

The layers of the seed coat may not be distinguishable or may even continue to be united with the fruit wall in certain monocots. When distinct, the outer layer is made up of hairy patterns or patches.

The characteristics of the ovules determine how many layers there are in the seed coat. The inner layer of bitegmic ovules either stays as a single layer or splits into two or three layers, which collect feeding items.

In turn, the outer layer has cells with tannin deposits, giving it a dark tint.

The outer layer keeps depositing various chemicals that make the seed coat cells’ walls thicker as they start to expand.

The ovules’ original attachment point to the ovary wall is symbolised by the hilum, an oval depression seen in the seed coat.

Some seeds’ seed coats may feature hair or wings that aid in wind-borne dissemination of the seed. Some seed coverings are built of watertight materials to avoid dehydration and decay while the seed is being dispersed by water.

  1. Endosperm
  • The endosperm is a collection of tissues that develop after fertilisation within the seed.
  • Endosperm cells are distinct because they have three sets of chromosomes per nucleus and are triploid.
  • Endosperm’s main function is to protect the embryo and provide it with nutrients.
  • Endospore development requires one of the sperm cells to fertilise with the diploid central cell of the female gametophyte. As a result, a principal endosperm cell with a triple fusion nucleus is produced.
  • Although most flowering plants are polyploid, some may be triploid or diploid in their chromosomal makeup.
  • In monocots, the endosperm is relatively large since it is the embryo’s main source of sustenance. However, in dicots, the two cotyledons are responsible for providing the nutrition.
  • The starchy endosperm cells, the basal transfer layer, and the aleurone layer are the three distinct cell types that make up the endosperm.
  • The starchy endosperm takes up the majority of the endosperm. Dead cells with protein structures and starch granules make up the endosperm.
  • The existence of cell wall ingrowths containing cell membranes that are up to 22 times bigger than those of regular plant cells distinguishes basal layer cells.
  • Even though the aleurone layer is just one cell thick in most monocots, it may be three layers thick. The layer encircles the embryo and the starchy endosperm.
  1. Embryo
  • Embryos are the straightforward multicellular structures made up of undifferentiated cells that are produced when a haploid egg cell is fertilised by a sperm cell.
  • DNA from the ovule and pollen combine to create the zygote, which makes up the embryo.
  • The embryo is a component of a seed and is shielded from outside elements like the endosperm and seed coat within the seed.
  • After fertilisation, the zygote goes through an asymmetrical initial cell division. As a consequence of the asymmetrical division, small and big cells combine to create an embryo as a consequence.
  • The bigger cell gives birth to the connective tissue, whilst the smaller apical cells ultimately evolve to produce components like stems, leaves, and roots. The endospore and the embryo are joined by the connective.
  • The embryo is divided into discrete zones where cell division takes place and parts where non-reproductive processes like metabolism, respiration, and storage take place as it continues to develop.
  • Of all the seed’s components, the embryo possesses the largest concentration of lipids and lipid-soluble vitamins.
  • Monocots have one bigger cotyledon, known as the scutellum, that is shield-shaped. The embryo is positioned in a groove at the endosperm’s one end.
  • Other components of the embryo axis, including the plumule, radicle, hypocotyl, and epicotyl, ultimately contribute to embryogenesis, the process by which a new plant is created.
  1. Plumule
  • The plumule is an embryonic component of the seed that ultimately grows into a shoot with leaves and stems.
  • It is sometimes referred to as the embryonic shoot and appears as a bud at one of the embryo’s axes.
  • When present inside the seed, the plumule is negatively geotropic, in contrast to radical, and may or may not have leaf structure.
  • Some plants, like sunflowers, don’t have leaf structure in the plumule, and growth doesn’t start until the cotyledons are visible above ground.
  • Others, however, have a leafy structure that grows through the soil while the cotyledons are still visible under the surface.
  • The coleoptile that surrounds the plumule in monocots is missing from the plumules of dicot seeds.
  1. Epicotyl
  • The part of the embryo that is located above the stalks of the seed leaves is known as the epicotyl, and it is crucial for the early phases of plant germination.
  • The epicotyl demonstrates hypogeal germination and develops more quickly than other regions of the embryo. The development of plumule above the soil while the cotyledons are still buried under the surface is known as hypogeal germination.
  • The expansion of the stem above the soil’s surface is caused by the development of the epicotyl area.
  • The point of attachment between the shoot apex and the embryo’s first genuine leaves is created by the proliferation of the cells in the epicotyl region.
  • Dicots and monocots have distinct ideas about what an epicotyl is. The epicotyl in dicots refers to the area of the shoot above the cotyledons, while the epicotyl in monocots refers to the shoot that emerges from the earth or the seed.
  1. Hypocotyl

The area of the seed known as the hypocotyls is found above the radicle and under the cotyledons, or seed leaves.

The cotyledons are pushed away from the soil surface during germination by the hypocotyl, which will later become a component of the stem.

Although it doesn’t develop as quickly as the epicotyl, the hypocotyl is the first part of the plant to poke its head out of the ground.

Because the epicotyl’s cells are sensitive and might be harmed during development, the hypocotyl and radical clear the way for it.

  1. Radicle

The part of the embryo that is the first to emerge from the seed during germination and subsequently gives rise to roots is known as the radicle.

Since the radicle descends downward into the soil and is positively geotropic, it is sometimes referred to as the embryonic root. Through the micropyle, the radicle exits the seed.

Depending on their orientation, radicels fall into one of two categories: antitropous radicles point away from the hilum on the seed coat, whereas syntropous radicles point in that direction.

In contrast to dicots, which lack this thin sheath, monocots have radicles that are encircled by the coleorhiza. The radicle does, however, have a root cap that guards it in the first stages of development.

  1. Cotyledon
  • The embryonic leaf in the seed, known as the cotyledon, takes up the majority of the seed’s volume and protects and nourishes the developing embryo.
  • One of the traits used to categorise flowering plants into distinct groups is the quantity of cotyledons present in a seed.
  • Dicotyledonous seeds are those that have two cotyledons, while monocotyledonous seeds only have one.
  • The cotyledons of dicot plants are similar to plant leaves in function and photosynthesis.
  • In monocot plants, the cotyledon is altered to become a scutellum, which serves to receive nourishment from the nearby endosperm and is not photosynthesised.
  • Cotyledons may have more than two, such as the approximately 24 found in pine and cypress trees.
  • Varying species have different cotyledon life spans; some may live just a few days, while others can last up to a year.

Functions of Monocot and Dicot Seed

The roles of monocot and dicot seeds are as follows:

The provision of suitable nutrition to the developing embryo is the primary role of seeds. The seed’s food store enables seedlings to develop more quickly than when they germinate from a spore.

The embryo is also shielded by the seed, which also permits the plant to spread successfully to other locations. Some seeds have characteristics that help them spread, such as fine hairs or water-resistant surfaces.

Dormancy is a process that seeds go through to shield the embryo from harsh circumstances.

As major sources of nutrients, including proteins and carbs, seeds from many plants are eaten as lentils or vegetables.

Monocot Seed vs Dicot Seed (10 Key Differences)

Characteristics Monocot Seed Dicot Seed
Definition Monocot seeds are defined as seeds that consist of a single (mono) embryonic leaf or cotyledon. Dicot seeds are defined as seeds that consist of two embryonic leaves or cotyledons.
Number of cotyledons Monocot seeds have a single cotyledon. Dicot seeds have two distinct cotyledons.
Cotyledons The cotyledons in monocot seeds are thin and small. The cotyledons in dicot seeds are fleshy and store food materials.
The cotyledons are mostly non-photosynthetic and absorb food from the adjacent endosperm. The cotyledons are photosynthetic and can produce food for the growing embryo.
Endosperm The endosperm is present which stores a large amount of food for the embryo. The endosperm is reduced or even absent.
Plumule The plumule in monocots occurs terminally. The plumule in dicots occurs laterally.
Coleorhiza Coleorhiza is present around the radicle in monocot seed. Coleorhiza is absent around the radicle in the dicot seed.
Coleoptile Coleoptile is present around the plumule in monocot seed. Coleoptile is absent in dicot seed.
Shape and size The shape and size of the monocot are variable, but these are usually less symmetrical and smaller in size. The shape and size of the dicot are variable, but these are usually more symmetrical and larger in size.
Seedpod The seed pod of monocots is usually trimerous. The seed pod of dicots can have numerous to zero seeds.

Examples of Monocot Seed

Maize seed

  • A single-seeded fruit known as the caryopsis contains the maize grain. Due to the ovary’s close association with the seed coat, these fruits are moncarpelate and indehiscent.
  • The term “kernel” refers to the maize caryopsis.
  • The embryo, endodermis, and carpel wall, or seed coat, are the three components that make up the grain or kernel.
  • The major portion of the seed is made up of endosperm, which comes in two different varieties: floury endosperm and horny endosperm.
  • The cotyledon, also known as the scutellum, which makes up the kernel’s embryo, is connected to the embryo axis via the scutellar node.
  • The scutellum is made up of four different tissues: perivascular tissue, parenchyma, epidermis, and epithelium.
  • Underneath the starchy endosperm lies a single cell layer known as the epithelium, which is composed mostly of hemicelluloses with very little cellulose.

Examples of Dicot Seed

Bean seed

  • The normal components of a dicot seed, such as the seed coat, endosperm, and embryo, are present in bean seeds.
  • Testa and tegmen, the two separate layers that make up the seed coat, are present. The tegmen is the inner layer, and the testa is the outer layer of the sperm.
  • A small hole in the seed coat on the testa’s surface permits water and nutrients to enter the embryo.
  • Underneath the seed coat, there are two cotyledons that are arranged symmetrically on the lateral sides.
  • The embryo, which has two primitive leaves on one of the terminal ends, is located between the cotyledons. On one of the terminals is the plumule, while on the other is the radicle.

References and Sources

  • Kruglova, N.N., Titova, G.E., Seldimirova, O.A. et al. Embryo of Flowering Plants at the Critical Stage of Embryogenesis Relative Autonomy (by Example of Cereals). Russ J Dev Biol 51, 1–15 (2020). https://doi.org/10.1134/S1062360420010026
  • Radchuk Volodymyr, Borisjuk Ljudmilla. Physical, metabolic and developmental functions of the seed coat. Frontiers in Plant Science. VOL 5, 2014, PAGES 510. DOI=10.3389/fpls.2014.00510
  • Mauricio A et al. (1993). Endosperm Origin, Development, and Function. The Plant Cell. Vol. 5, 1383-1399, October 1993.
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