Identifying the Different Parts of a Dicot Seed Embryo

Male and female gametes fuse to form the zygote during sexual reproduction. The zygote further undergoes division to evolve into an embryo. Monocots and dicots do not differ in the initial stages of development but they differ in the later stages of development.

Aim

To identify the different parts of an embryo of a dicot seed

Principle/Theory

The process of fertilization in plants leads to the formation of fruits which forms the ripened ovary. The seed can be one or many which form the mature ovule.

What does a seed consist of?

A seed consists of the following parts:

• Hilum – It is a scar that is located on the seed coat, associated with the stalk of the plant
• Seed coat – Forms the exterior covering of the plant, supplying with nourishment and protection to the seed inside
• Endosperm – It is the tissue containing nutrients for the growth of the embryo
• Embryo – Several divisions of the zygote gives rise to this structure.

What does the embryo consist of?

It consists of the following parts:

• Radicle
• Plumule
• Cotyledons

How are seeds classified?

On the basis of cotyledons in the seed, angiosperms can be classified into the following:

• Monocots
• Dicots

What is germination?

Germination is the process wherein the micropyle present in one part of the hilum takes up water. which under favorable conditions, such as suitable light, temperature, air, etc, it uses up for the seedlings to develop into tiny, immature embryonic plants from the seed coats.

Germination involves the following steps:

• Seeds swell, plumules develop into shoots
• From the radicle of the seeds, the roots arise
• Formation of cotyledons(one in monocots and two in dicots)

Material Required

• Seeds of red kidney bean/gram
• Forceps
• Magnifying glass
• Cloth
• Petri dish
• Water

Procedure

• Soak a few seeds overnight
• Next morning, drain the excess water out
• Now wrap the seeds in a clean and a moist cloth for a day, allow it to dry
• Next, carefully peel the seed coat
• With the help of forceps, dissect the seed so as to get two equal halves
• Examine with the help of a magnifying glass. Carefully identify and locate different parts of the seed
• Sketch out the interior of the seed you examined labeling all the parts as shown in the diagram.

Diagram

Observation

• The bean seed resembles the shape of a kidney. It has a convex and a concave side
• A scar known as the hilum is observed on the slightly darker side of the concave side
• A tiny pore known as the micropyle is located just adjacent to the hilum
• The seed is enclosed by a seed coat
• The embryo possesses two distinct and large cotyledons that resemble the shape of a kidney and are white in color
• Lateral attachment of the cotyledons to the curved embryonal axis is observed
• Radicle is examined. It is the rod-shaped and lightly protrusive lower end of the embryonal axis that is found placed towards the micropylar end.
• The upper end of the embryonal axis exhibits the plumule
• Hypocotyl is observed which is a section of the embryo axis found in between the radicle and adjunct of cotyledon leaves
• The epicotyl is also observed which is the section of the embryo axis between the adjunct of cotyledon leaves and plumule

Conclusion

Three principle parts of the embryo of dicot seeds are observed, they are:

• Cotyledons
• Plumule
• Radicle

Precautions

• Care needs to be taken while dissecting the seed as it may damage the seed
• The cloth that is used to wrap the seeds needs to be moist

Viva Questions

Q.1. How is a soaked seed different from a dry seed?

A.1. In comparison with a soaked seed, a dry seed has a wrinkled and a hard seed coat. The soaked seed has a softer seed coat that can be peeled easily

Q.2. In this experiment, why are seeds soaked overnight?

A.2. Seeds are soaked in order to assist the cotyledons for water absorption so as the embryo turns active

Q.3. What is the purpose of covering the seeds in the moist cloth?

A.3. It is for the growth of the baby plant furthermore.

Q.4. What does the cotyledon hold?

A.4. It provides nourishment for the growing plant.

Q.5. What is the significance of the seed coat?

A.5. During the dormant period, the seed coat shields the embryo and the cotyledons

Q.6. What does the radicle part of the embryo turn in the future?

A.6. The radicle goes on to develop into the root system

Q.7. List some of the conditions that are required for the seed to develop into a complete plant.

A.7. Following are the conditions required:

• Oxygen
• Water
• Suitable temperature
• Soil

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Further Reading