6.2. Structure of a Seed

Seeds may be of two main types:

• Monocotyledonous (Monocot) – One cotyledon (e.g., maize, wheat)
• Dicotyledonous (Dicot) – Two cotyledons (e.g., bean, gram)

Seeds are classified into two main types based on the number of cotyledons they have. The first type is called 'Monocotyledonous' or monocots, which have one cotyledon. An example of this type is maize. The second type is known as 'Dicotyledonous' or dicots, which have two cotyledons. An example of dicots is the common bean.

Think of cotyledons like the first leaves of a seed. If you imagine a seed sprouting, monocots like a maize seed only need one leaf to start, while dicots like a bean need two. It's like if you were starting a race; one runner might only need one shoe (the monocot), while another might need a pair (the dicot).

General Parts of a Dicot Seed (e.g., Bean Seed):

• Seed Coat – Outer protective covering; consists of two layers:
  • Testa – Outer layer
  • Tegmen – Inner thin layer
• Hilum – Scar on seed coat marking the point of attachment to the fruit
• Micropyle – Small pore near hilum; allows entry of water and oxygen
• Cotyledons – Two fleshy structures that store food
• Embryo – Develops into the new plant; consists of:
  • Radicle – Grows into root
  • Plumule – Grows into shoot

A dicot seed, like a bean seed, has several important parts. The 'seed coat' is the outer layer that protects the seed. It has two parts: the 'testa', which is the harder outer layer, and the 'tegmen', which is the thinner inner layer. The 'hilum' is a scar that shows where the seed was attached to the fruit. The 'micropyle' is a small opening near the hilum that allows water and oxygen to enter. The cotyledons are two fleshy parts that store food for the developing plant. Finally, the 'embryo' is the part that grows into the new plant, consisting of the 'radicle' that becomes the root and the 'plumule' that becomes the shoot.

Picture a seed as a tiny treasure chest. The seed coat is the tough outer shell that keeps everything inside safe. The hilum is like a small keyhole that shows where the treasure (the seed) was attached to its source. When the seed gets water through the micropyle, it's like finding a passcode to unlock the treasure chest, allowing the precious food and embryo to start growing.

Structure of a Monocot Seed (e.g., Maize Seed):

• Single cotyledon (Scutellum)
• Endosperm – Stores food for the embryo
• Embryo – With radicle and plumule
• Coleoptile – Protective sheath for the plumule
• Coleorhiza – Protective sheath for the radicle

In a monocot seed, such as a maize seed, there is one cotyledon known as the 'scutellum'. This single cotyledon is responsible for storing nutrients for the embryo, which is part of the seed that develops into the plant. The monocot seed also contains a tissue called the 'endosperm', which is rich in starch and provides food for the growing plant. The 'embryo' is still present, and it consists of the 'radicle', which will develop into the root, and the 'plumule', which will grow into the shoot. Additionally, the 'coleoptile' serves as a protective sheath for the plumule, and the 'coleorhiza' protects the radicle.

Think of a monocot seed like a small package with everything neatly packed. The scutellum is the one pocket that has all the snacks (food) for the plant to grow. The endosperm is like a big bag of chips, just waiting to be eaten. The coleoptile is like a protective cover over a fragile fruit, ensuring that it doesn't get damaged when it starts to grow. Just as we need protection when we are young and developing, so do seeds!

--