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5.7 - The Seed

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Introduction to Seeds

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Teacher
Teacher

Today, we will explore seeds, which are the results of fertilized ovules. Can anyone tell me what a seed consists of?

Student 1
Student 1

A seed has a seed coat and an embryo, right?

Teacher
Teacher

Exactly! The seed coat protects the seed, and the embryo is crucial for development. Who can describe the parts of a dicotyledonous seed?

Student 2
Student 2

The dicot seed has a testa, tegmen, hilum, micropyle, and two cotyledons.

Teacher
Teacher

Great job! Remember, the hilum is where the seed was attached to the fruit. Let's explore more about the embryo. What are the parts of the embryo?

Student 3
Student 3

The embryo consists of the radicle and the plumule!

Teacher
Teacher

Right! Remember this phrase: 'Radicle goes down, plumule goes up' to help you remember their positions. Any questions so far?

Student 4
Student 4

What about the endospermic seeds?

Teacher
Teacher

Excellent question! Endospermic seeds, like castor, contain additional food storage, whereas non-endospermic seeds don’t. Let's summarize: seeds protect the embryo and ensure its nourishment during growth.

Monocot vs. Dicot Seeds

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Teacher
Teacher

Now let’s look at the differences between monocot and dicot seeds. Can anyone identify the general features of monocot seeds?

Student 1
Student 1

They usually have one cotyledon and are endospermic.

Teacher
Teacher

Correct! In monocots, like maize, the seed coat is typically fused with the fruit wall. Now, what about dicot seeds?

Student 2
Student 2

Dicots have two cotyledons and can be non-endospermic.

Teacher
Teacher

Exactly! Remember, dicots like beans store food in their cotyledons instead of an endosperm. Let's do a quick recap. Can someone name a seed type and its features?

Student 3
Student 3

A gram seed is non-endospermic and has two cotyledons!

Teacher
Teacher

Spot on! This distinction is vital for understanding plant adaptation and evolution.

Seed Structure Review

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Teacher
Teacher

To solidify our understanding, let’s dissect the structures within the dicot seed again. What are the layers of the seed coat?

Student 4
Student 4

The outer layer is the testa and the inner one is the tegmen.

Teacher
Teacher

Correct! The seed coat protects the inner parts. Now who can explain the function of the micropyle?

Student 2
Student 2

The micropyle allows water to enter the seed for germination.

Teacher
Teacher

Right! The hilum is also significant as it reflects where the seed was attached to the fruit. What happens to the endosperm during germination in dicots?

Student 1
Student 1

It gets utilized for energy as the plant begins to grow.

Teacher
Teacher

Exactly! And in monocots, the endosperm often remains to nourish the developing plant. Remember these details as they are crucial in seed biology.

Introduction & Overview

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Quick Overview

The seed develops from fertilized ovules and consists of a seed coat and embryo, with structural differences between dicotyledonous and monocotyledonous seeds.

Standard

Seeds are the result of ovules after fertilization, made up of a seed coat and an embryo. Dicotyledonous seeds typically have two cotyledons while monocotyledonous seeds generally have one, often surrounded by an endosperm that serves as a food reserve.

Detailed

The Seed

The ovules, once fertilized, develop into seeds, which are crucial for the reproduction and survival of flowering plants. A seed consists primarily of two main parts: the seed coat and the embryo.

Structure of a Dicotyledonous Seed

  • Seed Coat: Comprising two layers—testa (outer) and tegmen (inner)—this protective coating shelters the inner components.
  • Hilum: A scar on the seed coat where it was attached to the fruit, and the micropyle, a small pore located above the hilum, allows germination.
  • Embryo: This section is made up of an embryonal axis and two cotyledons. Cotyledons are fleshy and packed with reserve food. The radicle and plumule are located at opposite ends of the embryonal axis.
  • Endospermic vs. Non-endospermic Seeds: Some seeds, like castor, contain an endosperm as food storage; others, such as gram and pea, do not retain endosperm in their mature seeds.

Structure of a Monocotyledonous Seed

Typically, monocot seeds are characterized by:
- Seed Coat: Generally membranous and fused with the fruit wall.
- Endosperm: Often bulky and serves as the primary food source engulfing the embryo, which resides in a groove at one end of the endosperm.
- Embryo: Contains one large cotyledon (scutellum) alongside a short axis with radicle and plumule. The protective sheaths surrounding the radical and plumule are known as coleorhiza and coleoptile, respectively.

The study of seeds, their structure, and their types is fundamental to understanding the life cycle of flowering plants, contributing significantly to their classification and biological functions.

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Audio Book

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Introduction to Seeds

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The ovules after fertilisation, develop into seeds. A seed is made up of a seed coat and an embryo. The embryo is made up of a radicle, an embryonal axis and one (as in wheat, maize) or two cotyledons (as in gram and pea).

Detailed Explanation

Seeds are the result of fertilization, which means that they start their journey after the male and female gametes unite. The seed is made of two main parts: the seed coat and the embryo. The seed coat is the protective outer layer that helps safeguard the seed from damage and dehydration. The embryo is the part that will develop into a new plant and consists of three parts: the radicle (which will grow into the root), the embryonal axis that connects the radicle to the cotyledons, and the cotyledons themselves that provide nutrition to the developing plant. Depending on the type of seed, there can be one or two cotyledons, which distinguishes between monocots (one cotyledon) and dicots (two cotyledons).

Examples & Analogies

Think of a seed like a packaged meal kit for cooking. The seed coat is like the packaging that keeps the kit safe during shipping, and the embryo is the ingredients and recipe inside that will eventually be put together to create a delicious dish—just as the seed eventually develops into a new plant.

Structure of a Dicotyledonous Seed

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The outermost covering of a seed is the seed coat. The seed coat has two layers, the outer testa and the inner tegmen. The hilum is a scar on the seed coat through which the developing seeds were attached to the fruit. Above the hilum is a small pore called the micropyle. Within the seed coat is the embryo, consisting of an embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food materials. At the two ends of the embryonal axis are present the radicle and the plumule.

Detailed Explanation

The structure of a dicot seed includes the seed coat, which is its outer layer made up of two parts: the outer layer called the testa and the inner layer called the tegmen. The hilum is a small scar on the seed coat indicating where the seed was attached to the fruit, and the micropyle is a tiny opening that allows water and nutrients to enter the seed when it begins to germinate. Inside the seed coat lies the embryo that consists of two fleshy cotyledons that store food, which is vital for the seedling's early growth. The embryonal axis connects the cotyledons to the radicle on one end (which will become the root) and the plumule on the other end (which will develop into the stem and leaves).

Examples & Analogies

Imagine the seed coat as the hard shell of a walnut. Just like the walnut protects the nut inside, the seed coat protects the inner components that are critical for growth. The hilum is like the small mark left where you cracked the shell to get to the nut, while the cotyledons are similar to the meat of the walnut, providing nourishment for the new plant as it begins to grow.

Structure of Monocotyledonous Seed

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Generally, monocotyledonous seeds are endospermic but some as in orchids are non-endospermic. In the seeds of cereals such as maize the seed coat is membranous and generally fused with the fruit wall. The endosperm is bulky and stores food. The outer covering of endosperm separates the embryo by a proteinous layer called aleurone layer. The embryo is small and situated in a groove at one end of the endosperm. It consists of one large and shield-shaped cotyledon known as scutellum and a short axis with a plumule and a radicle. The plumule and radicle are enclosed in sheaths which are called coleoptile and coleorhiza respectively.

Detailed Explanation

Monocot seeds are usually different from dicot seeds as they generally contain a structure called endosperm, which provides nutrition to the growing embryo. In cereal seeds like maize, the seed coat is thin and often attached to the fruit wall, which means it's less prominent. The endosperm is significant in size and is rich in nutrients, serving as a food reserve. The embryo within the endosperm is smaller, consisting of one main cotyledon called the scutellum. This cotyledon, along with the radicle and the plumule, is protected by sheaths known as coleoptile (for the plumule) and coleorhiza (for the radicle), helping to guide their growth.

Examples & Analogies

Consider a monocot seed similar to a small bag of rice. The rice grain (endosperm) provides energy and nourishment for cooking, while the thin outer layer is like the seed coat. The tiny embryo inside the rice grain is like a small sprout waiting to grow when it's planted in the right conditions, just like rice grows into a new rice plant when conditions are favorable.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Seed Structure: A seed is made up of a seed coat and an embryo. The seed coat protects the embryo, which will develop into a new plant.

  • Dicotyledonous Seeds: These seeds have two cotyledons, a hilum, a micropyle, and can be endospermic or non-endospermic.

  • Monocotyledonous Seeds: Typically consist of one cotyledon, a prominent endosperm, and are characterized by their storage of food.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Example of a dicotyledonous seed: Gram has two cotyledons and is non-endospermic.

  • Example of a monocotyledonous seed: Maize has one cotyledon and is endospermic.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Coat on the seed, protects with ease, hilum says where it clung, mpyle lets water run.

📖 Fascinating Stories

  • Once upon a time in the land of seeds, the hilum and micropyle formed a bond. The hilum proudly displayed its scar, while the micropyle welcomed water to a future star—the plant!

🧠 Other Memory Gems

  • To remember the parts of a dicot seed: H for Hilum, M for Micropyle, C for Cotyledons, E for Embryo.

🎯 Super Acronyms

Remember 'SCEM' for Dicot Seeds

  • S: for Seed coat
  • C: for Cotyledons
  • E: for Embryo
  • M: for Micropyle.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Seed Coat

    Definition:

    The protective outer layer of a seed comprising the testa and tegmen.

  • Term: Embryo

    Definition:

    The part of the seed that develops into a new plant, consisting of the radicle, cotyledons, and plumule.

  • Term: Hilum

    Definition:

    A scar on the seed coat indicating the point of attachment to the fruit.

  • Term: Micropyle

    Definition:

    A small pore in the seed coat allowing water to enter for germination.

  • Term: Endospermic Seed

    Definition:

    Seeds that contain endosperm as a food source for the embryo.

  • Term: NonEndospermic Seed

    Definition:

    Seeds that do not retain endosperm in mature form, relying instead on their cotyledons for nutrition.

  • Term: Cotyledon

    Definition:

    The first leaf or leaves that appear from a germinating seed.