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After the process of fertilization, ovules are converted into seeds, which contain cotyledons. Cotyledons are formed in the process of embryogenesis and are present in the seeds before germination. Therefore, cotyledons are often known as seed leaves. They play a vital role in the early stages of plant development. Though they’re called the seed leaves they’re not true leaves. They usually consist of two types of parenchyma cells.
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Keyterms: Seed, Fertilization, Plant, Germination, parenchyma cells, leaves, Monocotyledon, Dicotyledon
Read More: Basic Internal Anatomy of Leaf
Cotyledon: Definition
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A leaf that is stored in a seed is known as a cotyledon. In other words, the first leaves that appear on the plant after the seed sprouts are the cotyledons.Cotyledons are not considered true leaves because of their different appearance from other leaves. They generally store food materials and contribute to the growth of true leaves by helping plants to make sugar through photosynthesis. Cotyledons are of two types-
- Monocotyledon
- Dicotyledon
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Monocotyledonous Seeds
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Seeds having one embryonic leaf are called monocotyledonous seeds. In monocotyledonous seeds, the seed covering is membrane-like and attached to the fruit wall. Pasture grasses, bamboo, rice, wheat, maize, etc. are some examples of monocots.
Terms Related to Monocotyledonous Seeds
- Aleurone Layer- A living endospermic cell enclosing and separating the embryo by a proteinaceous layer is known as the aleurone layer.
- Scutellum- In certain monocots, a large and shield-like cotyledon is present, which is known as the scutellum.
- Coleoptile and Coleorhiza- Coleoptile and Coleorhiza are responsible for providing cover to the plumule and radical in a monocot. The protective sheath covering plumule is coleoptile and the protective sheath covering radical is coleorhiza.
Dicotyledonous Seeds
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Seeds having two embryonic leaves are called dicotyledonous seeds or dicots. In dicots, seed covering has two layers. As a result of double fertilization, the endosperm is formed in some seeds (e.g. castor). Bean, gram, pea, etc. are some examples of dicots.
Terms Related to Dicotyledonous Seeds
- Testa and Tegmen- In dicots there are two seed coverings, the outer covering is called the testa and the inner covering is called the tegmen.
- Hilum- A scar is left on the seed coat of a dicotyledonous seed due to its former attachment to the ovary wall, this scar or mark on the seed coat is called the hilum.
- Micropyle- Micropyle is a small pore above the hilum, through which the pollen tube penetrates.
Difference between Monocotyledon and Dicotyledons
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The table below gives the difference between monocots and dicots based on different parameters-
| Parameter | Monocot | Dicot |
|---|---|---|
| Flowers | Trimerous: Have three flower parts. | Tetramerous or Pentamerous- Have flower parts in the multiple of four or five. |
| Pollen | Pollen has one pore. | Pollen has three pores. |
| Stems | Vascular bundles in the stem are scattered. | Vascular bundles in the stem are arranged in a ring. |
| Roots | Adventitious/Fibrous Roots- Develop on stems and leaves. | Tap Roots- Develop from the radical primary root and lateral roots. |
| Leaves | Leaf veins are parallel. | Leaf veins are reticulated (form a net-like structure). |
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Things to Remember
- Cotyledons are the embryo leaves, which are stored in the seeds.
- Monocotyledonous seeds and Dicotyledonous seeds are the two types of cotyledon seeds.
- The covering in monocot seed is called the aleurone layer.
- The coverings in dicot seed are called the testa and tegmen.
- Monocots have fibrous roots, while dicots have taproots.
Previous Year Questions
- Which one of the following statements about Cycas is incorrect?[NEET 1998]
- In Pinus; the pollen grain has 6 chromosomes then in its endosperm will have...[NEET 1992]
- A plant having seeds but lacking flowers and fruits belongs to...[NEET 1992]
- Which one of the following is not common between Funaria and Selaginella….[NEET 1992]
- The plant group that produces spores and embryo but lacks vascular tissues and seeds is….[NEET 1992]
- A plant in which sporophytic generation is represented by zygote is...[NEET 1992]
- Select the correct statement….[NEET 2016]
- Protonema occurs in the life cycle of….[NEET 1990]
- Moss peristome takes part in...[NEET 1990]
- The pyrenoids are made up of...[NEET 1995]
- The plant body of moss (Funaria) is...[NEET 1995]
- A well developed archegonium with neck consisting of 4-6 rows and neck canal cells, characterises...[NEET 1995]
- In bryophytes….[NEET 1994]
- Which one of the following is considered important in the development of seed habit?...[NEET 2009]
- Which of the following is without exception in Angiosperms : -...[NEET 2002]
- An example for artificial system of classification is
- A microsporophyll in Pinus has
- Which of the following pteridophyte is heterosporous in nature?
- Which of these is mismatched ?
- Which one of the following is called maiden-hair fern ?
Sample Questions
Ques. How many types of cotyledon seeds are there? (1 Mark)
Ans. There are two types of cotyledon seeds, monocotyledonous seed and dicotyledonous seed.
Ques. Why are cotyledons known as seed leaves? (1 Mark)
Ans. Because of their appearance in the seed and their leaf-like structure, cotyledons are called seed leaves. However, cotyledons are not considered true leaves.
Ques. What is the function of cotyledons? (2 Marks)
Ans. Cotyledons are responsible for the growth of the plant and other leaves in the early stages of plant development. They store food materials and also perform the process of photosynthesis. They usually die after some time.
Ques. Give the two characteristics used to classify dicotyledons in 3 sub-classes. (1 Mark)
Ans. The sub-classes are usually divided into series mainly on the basis of the position of ovary with respect to other floral parts.
Ques. Differentiate between gymnosperms and angiosperms. (3 Marks)
Ans.
| Gymnosperms | Angiosperm |
|---|---|
| The sporophylls form cones. | The sporophylls produce flowers. |
| Microporosphyll contain micro-sporangia bearing microspores. | Microsporophyll has two parts: anther and filament. |
| Stigma and style are not present | Stigma and style are there. |
| Ovule is there at the lower side and exposed to the megasporophyll. | Ovules are attached to the funic-ulus and are present inside the ovary. |
| More than two cotyledons are present. | Only one or two cotyledons are present. |
| There is no fruit formation. | Fruit formation happens. |
| Double fertilization does not happen. | Double fertilization happens. |
Ques. Differentiate between monocotyledons and dicotyledons. (3 Marks)
Ans: The table below gives the difference between monocots and dicots based on different parameters-
| Parameter | Monocot | Dicot |
|---|---|---|
| Flowers | Trimerous: Have three flower parts. | Tetramerous or Pentamerous- Have flower parts in the multiple of four or five. |
| Pollen | Pollen has one pore. | Pollen has three pores. |
| Stems | Vascular bundles in the stem are scattered. | Vascular bundles in the stem are arranged in a ring. |
| Roots | Adventitious/Fibrous Roots- Develop on stems and leaves. | Tap Roots- Develop from the radical primary root and lateral roots. |
| Leaves | Leaf veins are parallel. | Leaf veins are reticulated (form a net-like structure). |
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