Seed Germination & Seed Structure

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Questions and Answers

Explain how seed germination is crucial for both crop yield and quality.

Seed germination is the fundamental process by which plants grow from a single seed and directly determines the success of crop establishment, influencing both the quantity (yield) and the desired attributes (quality) of the harvest.

Describe the protective function of the seed coat and its composition.

The seed coat is the outermost covering of a seed that provides physical protection against environmental factors and pathogens. It typically consists of two layers and is the solid component of the seed.

What is the role of the endosperm, and how does it differ between monocotyledonous and dicotyledonous seeds?

The endosperm is a tissue inside seeds that stores food to nourish the developing embryo. It is bulky and generally present in monocotyledonous seeds, whereas dicotyledonous seeds often have little to no endosperm, as the cotyledons take over the food storage function.

What are the three main components of the plant embryo and mention what each component eventually develops into?

<p>The three main components of the plant embryo are the radicle, plumule, and cotyledon. The radicle develops into the root system, the plumule develops into the shoot system, and the cotyledons provide nourishment to the developing seedling.</p> Signup and view all the answers

Compare and contrast endospermic and non-endospermic seeds.

<p>Endospermic seeds contain endosperm tissue that nourishes the developing embryo. Non-endospermic seeds lack endosperm, instead storing nutrients in their cotyledons.</p> Signup and view all the answers

How does water serve as a critical factor in germination, affecting enzymatic activity?

<p>Water is essential for germination by hydrating tissues and activating enzymes. Specifically, water triggers enzymes responsible for converting stored starch into sugars, which provide energy for the growing embryo.</p> Signup and view all the answers

Explain the dual role of light in seed germination.

<p>Light can either stimulate or inhibit seed germination depending on the plant species and other factors. Some seeds require light exposure to germinate, while others germinate better in darkness.</p> Signup and view all the answers

Describe the importance of oxygen in cellular respiration during germination.

<p>Oxygen is essential for cellular respiration, which provides the energy needed for metabolic processes during germination. In the presence of moisture, oxygen allows the seed to start metabolism and fuel the initial stages of growth.</p> Signup and view all the answers

How can soil temperature impact germination, and why is an optimal temperature crucial?

<p>Soil temperature greatly influences germination percentage and rate as it affects the enzymatic activity and metabolic processes within the seed. There is an optimal soil temperature range for each species that maximizes germination success.</p> Signup and view all the answers

What is seed dormancy, and how can it be advantageous or disadvantageous?

<p>Seed dormancy is a condition where seeds are prevented from germinating even under favorable conditions. This can be advantageous by preventing germination in unsuitable conditions, but disadvantageous when immediate propagation is desired.</p> Signup and view all the answers

Explain how the elongation of the hypocotyl contributes to epigeal germination.

<p>Epigeal germination involves the rapid elongation of the hypocotyl, which pushes the cotyledons above the ground. After emerging, the hypocotyl straightens, and the cotyledons become green as the seedling develops.</p> Signup and view all the answers

Describe the fate of the cotyledons in epigeal germination.

<p>In epigeal germination, the cotyledons are brought above the ground, turn green, and may function in photosynthesis for a short period. Eventually, the cotyledons fall off the seedling as the plant develops true leaves.</p> Signup and view all the answers

How does the epicotyl contribute to hypogeal germination?

<p>Hypogeal germination relies on the elongation of the epicotyl, which is the embryonic axis between the plumule and cotyledons. The elongating epicotyl pushes the plumule out of the soil, while the cotyledons remain underground.</p> Signup and view all the answers

What are some key differences between hypogeal and epigeal germination?

<p>In hypogeal germination, the cotyledons remain underground, and the epicotyl elongates to push the plumule to the surface. In epigeal germination, the hypocotyl elongates, pulling the cotyledons above the ground. Whether the cotyledons emerge or stay below the surface is the key difference.</p> Signup and view all the answers

In hypogeal germination, what part of the plant emerges from the soil, and where do the cotyledons remain?

<p>In hypogeal germination, the plumule is the part of the plant that emerges from the soil, while the cotyledons remain below the surface.</p> Signup and view all the answers

What is the significance of stored food in seeds for successful germination and seedling establishment?

<p>Stored food in seeds provides the initial energy and nutrients required for the embryo to grow and develop into a seedling before it can photosynthesize. It supports early metabolic processes and structural development.</p> Signup and view all the answers

Explain how temperature affects not only the germination percentage but also the rate of germination.

<p>Temperature affects the rate of enzymatic reactions necessary for germination, influencing how quickly seeds germinate. It also affects the total number of seeds that successfully germinate at a given temperature.</p> Signup and view all the answers

Why is adequate and continuous supply of water necessary for complete emergence during seed germination?

<p>Adequate water is necessary for complete emergence as it hydrates seed tissues, activates enzymes for starch conversion, and facilitates nutrient transport. Without a continuous water supply, these processes halt, preventing successful germination.</p> Signup and view all the answers

Describe what happens to the seed coat after the hypocotyl straightens during epigeal germination.

<p>Once the hypocotyl straightens in epigeal germination, the seed coat loosens and falls down, revealing the cotyledons, which may then turn green.</p> Signup and view all the answers

How do monocotyledonous and dicotyledonous embryos differ, particularly in the number of cotyledons?

<p>Monocotyledonous embryos have one cotyledon, while dicotyledonous embryos have two cotyledons. These cotyledons serve different roles in nourishment and development.</p> Signup and view all the answers

Flashcards

Seed Germination

The process by which plant species grow from a single seed into a plant, influencing crop yield and quality.

Seed

A plant enclosed in a covering called the seed coat, usually with stored food.

Seed Coat

Outermost covering of a seed with two layers.

Endosperm

Tissue produced inside seeds that stores food.

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Embryo

Small part of the seed situated in a groove at one end of the endosperm.

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Radicle

Part of the embryo that develops into the root system.

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Plumule

Part of the embryo that develops into the shoot system.

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Water importance in germination

Important factor, necessary for complete emergence and a triggering enzyme for starch conversion into sugar.

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Seed Dormancy

Seeds are prevented from germinating even under favorable conditions.

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Epigeal germination

Cotyledons are brought above the ground due to rapid elongation of hypocotyl.

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Hypogeal Germination

Cotyledons do not come out of the soil surface.

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Study Notes

  • Seed germination is a crucial phase of plant growth and development.
  • Germination is the fundamental process of plant species growing from a single seed.
  • Germination influences crop yield and quality.
  • A common example of seed germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm.

What is the Seed

  • A seed is a small embryonic plant enclosed in a seed coat, typically with stored food.
  • Seeds are the product of the ripened ovule of gymnosperm and angiosperm plants.
  • Seed development occurs after fertilization and some growth within the mother plant.

Seed Types and Structure

  • Seeds have two primary types: monocotyledonous and dicotyledonous.
  • Monocotyledonous seeds examples: wheat and maize.
  • Dicotyledonous seeds examples: Beans and castor.

Structure of Seed

  • The seed coat is the seed's outermost covering with two layers, generally a solid component.
  • The endosperm is a bulky tissue produced inside seeds that stores food.
  • Monocotyledonous seeds are generally endospermic, while some, like orchids, are non-endospermic.
  • Seeds divide into endospermic and non-endospermic types.
  • The embryo is small and situated in a groove at one end of the endosperm.
  • The embryo develops after a fertilized stage.
  • The main parts of the embryo are the radicle, plumule, and cotyledon.
  • Radicle- growth becomes the root system under the soil surface
  • Plumule- groth becomes the shoot system above the soil surface
  • Cotyledons are often fleshy and full of reserve food materials.
  • There are two types of cotyledons present in flowering plants:
  • Monocotyledonous/monocots feature embryos with one cotyledon.
  • Dicotyledonous/dicots feature embryos with two cotyledons.

Germination Factors

  • Water is the most important factor in germination.
  • Continuous water supply is necessary for complete emergence.
  • Water triggers enzymes for starch conversion into sugar.
  • Light is another key germination factor and can stimulate or inhibit seed germination.
  • Oxygen is necessary in the presence of enough moisture for cellular respiration, which allows start of metabolism and for plants to grow.
  • A favorable temperature is necessary for plant growth and affects germination percentage and rate.
  • Each seed species has an optimal soil temperature for germination.
  • Seed dormancy is a condition preventing seeds from germinating even under favorable conditions to complete maturity.

Types of Germination

  • Epigeal Germination: Cotyledons are brought above ground due to rapid hypocotyl elongation; cotyledons fall down ultimately
  • Hypogeal Germination: Cotyledons remain below the soil surface as the epicotyl elongates, pushing the plumule out of the soil.

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