A seed is the final product of the sexual reproduction process in flowering plants, serving as the primary unit for the propagation of a new generation. Its structure is a marvel of biological packaging, typically consisting of the seed coat, the embryo, and stored food. The tough outer seed coat provides essential protection from physical injury, insects, and diseases. Inside lies the embryo, which is the miniature future plant, composed of the radicle that develops into the root, the plumule that becomes the shoot, and one or two cotyledons. These cotyledons are significant as they store the vital food reserves necessary for the embryo’s survival and initial growth. In some seeds like beans, these are prominent and fleshy, while in others like grasses, the food is stored in a separate tissue called the endosperm.
The process by which this dormant embryo awakens and grows into a seedling is known as germination. For this process to begin, certain external conditions must be met, including the presence of water, a suitable temperature, and an adequate supply of oxygen. Water is crucial for softening the seed coat and activating the enzymes that convert stored food into a soluble form. Oxygen supports the high respiratory activity needed to provide energy for growth. Based on the behavior of the cotyledons during this process, germination is classified into two main types. In epigeal germination, the cotyledons are pushed above the soil surface by the growth of the hypocotyl, as seen in castor or bean seeds. Conversely, in hypogeal germination, the cotyledons remain underground while the epicotyl elongates, bringing only the plumule above the soil, which is characteristic of seeds like peas or maize.
Understanding the structure of a seed and the process of germination is fundamental in biology and has immense practical importance. This knowledge is directly applied in agriculture to improve crop yields. Farmers use this information to select high-quality seeds and create the optimal conditions for sowing, ensuring a higher rate of successful germination. By managing factors like soil moisture, temperature, and aeration, they can maximize the chances of a healthy crop stand, forming the very foundation of food production and sustainable farming practices worldwide.
- Multiple choice type
Question 1.
Which one of the following plant parts is correctly matched with one of its stated characteristics?
- Mango seed – aleurone layer
- Bean seed – endosperm
- Maize grain – coleoptile
- Wheat grain – exalbuminous
Question 2.
Seeds sown very deep in the soil fail to germinate because they
- cannot exert enough force to push the soil upward.
- do not get enough sunlight.
- get too much water.
- do not get enough oxygen.
- Very short answer type
Question 1.
1. Is the following statement true (T) or false (F)? Maize grain is fruit and not a seed. (T/F)
True
False
2. Is the following statement true (T) or false (F)? Seeds fell in a flower-bed from the previous crop usually do not germinate until the next sowing season.
True
False
3. Is the following statement true (T) or false (F)? Oxygen is necessary for the germination of seeds.
True
False
Ans:
Here are the evaluations for each statement:
- Is the following statement true (T) or false (F)? Maize grain is fruit and not a seed.
- True (T). The maize grain is technically a fruit called a caryopsis (or grain), where the fruit wall (pericarp) is fused to the seed coat (testa). Biologically, we consume the whole fruit, not just the separated seed.
- Is the following statement true (T) or false (F)? Seeds fallen in a flower-bed from the previous crop usually do not germinate until the next sowing season.
- True (T). This is generally true due to seed dormancy. The seeds require specific conditions (like a period of cold, specific light exposure, or leaching of germination inhibitors by rain) that are often not met immediately, preventing them from germinating prematurely until the suitable growing season arrives.
- Is the following statement true (T) or false (F)? Oxygen is necessary for the germination of seeds.
- True (T). Seeds respire aerobically during germination to generate the large amount of energy (ATP) required for cell division and growth. This process requires a sufficient supply of oxygen (O2).
Question 2.
1. Name the following : A monocotyledonous endospermic seed.
2. Name the following : A chemical used in experiments which absorbs oxygen.
3. Name the following: Part of the plumule above the embryonic axis of the seed.
4. Name the following : A plant that shows viviparous germination.
5. Name the following : The layer of the endosperm of maize is rich in protein.
6. Name the following : A seed with folded plumule leaves.
Ans:
Here are the names corresponding to the descriptions:
- A monocotyledonous endospermic seed: Maize (or Wheat, Rice)
- A chemical used in experiments which absorbs oxygen: Alkaline pyrogallol (or Potassium hydroxide (KOH) for CO2 absorption, often used alongside a control for O2 experiments)
- Part of the plumule above the embryonic axis of the seed: Epicotyl
- A plant that shows viviparous germination: Rhizophora (or Mangrove)
- The layer of the endosperm of maize is rich in protein: Aleurone layer
- A seed with folded plumule leaves: Bean seed (or any dicot seed like pea, gram)
Question 3.
Is the following statement true (T) or false (F)? Some seeds have no cotyledons at all.
True
False
Ans:
The statement “Some seeds have no cotyledons at all” is False (F).
Rationale:
By definition, a seed is an embryonic plant enclosed in a protective outer covering. The cotyledons are essential embryonic leaves that are part of the seed embryo.
- They are necessary for the young seedling’s survival, as they function either for food storage (in most dicots like beans and peanuts) or for absorption of food stored in the endosperm (in monocots like maize).
- All true seeds must contain at least one cotyledon. The major classifications of flowering plants are based on the number of cotyledons present: Monocots (one cotyledon) and Dicots (two cotyledons).
Question 3.
1. Fill in the blanks: In bean seeds, ______ grows faster and the seeds are brought ______ ground.
2. Fill in the blanks: _______ is a protective layer of radicle and ________ protects the rolled plumule.
3. Fill in the blanks: A seed is protected by ________ and __________ .
4. Fill in the blanks: Seeds absorb water through __________ which also helps in the diffusion of respiratory gases.
5. Fill in the blanks: Rich, wheat and maize are rich in _________ food.
Ans:
- In bean seeds, hypocotyl grows faster and the seeds are brought above ground.
- Coleorhiza is a protective layer of radicle and coleoptile protects the rolled plumule.
- A seed is protected by testa and tegmen (the two layers of the seed coat).
- Seeds absorb water through micropyles which also helps in the diffusion of respiratory gases.
- Rice, wheat, and maize are rich in carbohydrate (or starchy) food.
Question 4.
1. Arrange the following set of a term in order, so as to be in a logical sequence. Rewrite the correct order. Embryo, 1st male gamete, zygote, egg cell, micropyle.
2. Arrange the following set of a term in order, so as to be in a logical sequence. Rewrite the correct order. Zygote, embryo, seed, allogamy, fusion of gametes.
3. Arrange the following set of a term in order, so as to be in a logical sequence. Rewrite the correct order. Seed coat bursts, hypocotyls elongate, radicles grow downward, hypocotyls form a loop above the soil, epicotyls elongates.
Ans:
- Short answer type
Question 1.
What is the difference between an embryo and a seed?
Ans:
| Feature | Embryo | Seed |
| Definition | The tiny, rudimentary plant formed from the division of the fertilized egg (zygote). It is the true living offspring. | The mature, fertilized ovule that develops after fertilization. It is the complete dispersal and survival unit. |
| Composition | Consists of the Plumule (embryonic shoot), Radicle (embryonic root), and Cotyledon(s). | Consists of three main parts: 1. Embryo (living part) 2. Seed Coat (protection) 3. Stored Food (Endosperm or Cotyledons). |
| Origin | Formed from the Zygote (fertilized egg cell). | Formed from the Ovule (the entire structure surrounding the egg cell). |
| Scope | Part of the seed; an internal, biological component. | Contains the embryo; the entire, protective structure. |
| Function | To grow into a new plant (germination). | To protect the dormant embryo and provide initial nutrition. |
Question 2.
Give two examples each of endospermic (albuminous) seeds, and non-endospermic (exalbuminous) seeds.
Ans:
| Classification | Food Storage Location | Example 1 | Example 2 |
| Endospermic (Albuminous) | Food stored in the endosperm. | Maize (Corn) | Castor |
| Non-Endospermic (Exalbuminous) | Food stored in the cotyledons. | Pea | Bean |
Question 3.
Germinated grams are considered highly nutritive. What is the reason for this belief?
Ans:
Germinated grams (sprouts) are considered highly nutritive because the process of germination triggers rapid biochemical changes that significantly enhance the availability and quality of nutrients compared to the dry seed.
This nutritional boost occurs for three main reasons:
1. Increased Nutrient Availability and Synthesis
The dormant seed’s stored food is broken down to fuel the growing embryo:
- Vitamins increase: There is a significant increase in certain vitamins, most notably Vitamin C, which is often trace or absent in the dry seed. Levels of some B vitamins (like Folate) also increase.
- Simple Sugars: Complex carbohydrates (starches) are broken down by enzymes into simpler sugars (like glucose), making them a quick source of energy and easier to digest.
- Amino Acids: Complex proteins are broken down into easily digestible amino acids (the building blocks of protein), often increasing the overall bioavailability and quality of the protein.
2. Reduction of Anti-Nutrients
The sprouting process effectively reduces or neutralizes anti-nutrients, which are compounds that inhibit the body’s ability to absorb essential minerals and vitamins.
- Phytic Acid (or phytates), which binds to minerals like iron and zinc, is significantly reduced, making those minerals more accessible for absorption.
3. Increased Enzyme Activity and Digestibility
Germination activates and produces high levels of digestive enzymes.
- These enzymes pre-digest the stored food (as noted above), which makes the overall grams much easier on the human digestive system than eating the hard, uncooked dry seed. This leads to less bloating and better nutrient absorption.
Question 4.
Why do we not use the terms maize fruit and maize seed? What do we say instead?
Ans:
We typically avoid the simple terms “maize fruit” and “maize seed” because the structure we eat is biologically unique, blurring the lines between the two definitions.
Why “Fruit” and “Seed” Are Not Precise
The maize kernel is botanically a fruit, but it doesn’t function like a typical fruit:
- It’s a Fruit: The entire kernel develops from the ripened ovary of the flower, which is the botanical definition of a fruit.
- It’s Not a Distinct Seed: In maize (and all grasses), the fruit wall (pericarp) is completely and permanently fused with the seed coat (testa). The resulting structure is a single, protective unit. Since the seed is not easily separable from the fruit wall, calling it strictly a “seed” is inaccurate, and calling it a “fruit” is also incomplete given its dry nature.
What We Say Instead
The correct terms used instead are:
- Maize Grain: This is the common and most appropriate term, referring generally to the edible structure of cereal crops where the seed coat and fruit wall are fused.
- Caryopsis: This is the precise botanical term for this specific type of dry, simple fruit, which is characteristic of the entire grass family (Poaceae), including wheat, rice, and maize.
The unique structure of the maize kernel, where the seed and fruit wall are inseparable, necessitates the use of the specific term caryopsis, or the common term grain.
- Long answer type
Question 1.
1. What is the function of the following in a seed? Seed coat
2. What is the function of the following in a seed? Micropyle
3. What is the function of the following in a seed? Cotyledons
4. What is the function of the following in a seed? Radicle
5. What is the function of the following in a seed? Plumule
Ans:
Here are the functions of the specified parts within a seed:
- Seed Coat (Testa):
- Function: To provide protection to the delicate embryo inside from mechanical injury, extreme temperatures, and desiccation (drying out). It may also prevent the entry of bacteria and fungi.
- Micropyle:
- Function: To allow water and oxygen to enter the seed during germination. The micropyle is a tiny pore or scar on the seed coat that corresponds to the opening in the ovule.
- Cotyledons (Seed Leaves):
- Function: To serve as the primary storage site for food (proteins, fats, and starch) in non-endospermic seeds (like beans and peas), providing nourishment to the growing embryo during germination. In endospermic seeds (like maize), they function mainly in absorbing nutrients from the endosperm.
- Radicle:
- Function: The embryonic root. Its function is to be the first structure to emerge from the seed during germination, developing into the primary root system to anchor the plant and absorb water and minerals.
- Plumule:
- Function: The embryonic shoot. Its function is to develop into the primary shoot system, consisting of the stem and future leaves, allowing the plant to begin photosynthesis.
Question 2.
Suggest an experiment to prove that a suitable temperature is necessary for germination.
Ans:
Experiment to Prove Suitable Temperature is Necessary for Germination
This experiment demonstrates that temperature is a critical, limiting factor for seed germination by testing seeds under three different thermal conditions while keeping water and oxygen constant.
Aim
To prove that a suitable temperature is necessary for the germination of seeds.
Materials Required
- Three identical beakers or test tubes (A, B, and C).
- Moist cotton wool.
- An equal number of identical healthy seeds (e.g., kidney beans).
- Water.
- Refrigerator, an area for room temperature, and an incubator or hot water bath.
Procedure
- Standardize Conditions: Line the base of all three containers (A, B, and C) with moist cotton wool and place an equal number of seeds in each. Ensure the cotton wool is damp, but not saturated, to guarantee adequate oxygen supply.
- Establish Variables: Place the three containers in three distinct thermal environments:
- Beaker A (Optimal Control): Placed at room temperature . , which is optimal for most seeds.
- Beaker B (Low Temperature): Placed in a refrigerator .
- Beaker C (High Temperature): Placed in a warm location or incubator .
- Observe: Monitor the seeds over the course of 3 to 5 days, maintaining the moisture level equally in all containers.
Question 3.
Sometimes the potatoes kept in a basket during the late rainy season start giving out small shoots. Would you call it germination? Give reasons in support of your answer.
Ans:
| Feature | Sprouting Potato (Vegetative Propagation) | Germination (of a True Seed) |
| Starting Part | Starts from a vegetative part (the potato tuber is a modified stem) and involves the growth of pre-existing axillary buds (the “eyes”). | Starts from a seed, which is a specialized reproductive unit containing a dormant embryo (radicle and plumule). |
| Reproduction Type | A form of asexual reproduction, producing a genetically identical clone of the parent plant. | The result of sexual reproduction involves the development of a new, genetically distinct sporophyte plant. |
| Process | Involves the breaking of bud dormancy and the growth of the shoots and roots directly from the tuber’s stored food. | Involves the activation of a dormant embryo and the emergence of the radicle and plumule after breaking seed dormancy. |
Question 4.
1. Give two differences in the following pairs : Epigeal germination and hypogeal germination
2. Give Two Differences in the Following Pairs: Coleorhiza and coleoptile
3. Give two differences in the following pairs: Bean seed and maize grain
Ans:
1. Epigeal Germination and Hypogeal Germination
| Feature | Epigeal Germination (e.g., Bean, Castor) | Hypogeal Germination (e.g., Pea, Maize) |
| Cotyledons | The cotyledons are brought above the soil surface by the elongation of the hypocotyl. | The cotyledons remain below the soil surface, as the epicotyl elongates. |
| Hypocotyl/Epicotyl | The hypocotyl (part below the cotyledons) elongates rapidly and forms a characteristic loop. | The epicotyl (part above the cotyledons) elongates rapidly, carrying the plumule up. |
2. Coleorhiza and coleoptile
| Feature | Coleorhiza | Coleoptile |
| Structure Covered | It is the protective sheath covering the embryonic radicle (the root tip). | It is the protective sheath covering the embryonic plumule (the shoot tip). |
| Function | It protects the radicle as it pushes through the soil during germination. | It protects the young leaves of the plumule as they push through the soil. |
3. Bean seed and maize grain
| Feature | Bean Seed | Maize Grain (Caryopsis) |
| Structure | It is a true seed (seed coat and fruit wall are separate). | It is a fruit (caryopsis) where the seed coat and fruit wall are permanently fused. |
| Cotyledons | Dicotyledonous (has two large cotyledons) and is exalbuminous (food is stored in the cotyledons). | Monocotyledonous (has one cotyledon, called the scutellum) and is albuminous (food is stored mainly in the endosperm). |
Question 5.
Differentiate between germination and vivipary.
Ans:
| Feature | Germination | Vivipary |
| Definition | The process where a dormant embryo within a mature seed resumes growth and develops into a seedling after the seed is shed from the parent plant. | The phenomenon where the seed germinates while still attached to the parent plant and receiving nourishment from it. |
| Location | Occurs ex-situ (outside the parent fruit), usually in the soil or a suitable medium. | Occurs in-situ (inside the parent fruit) and while the fruit is still attached to the parent plant. |
| Seed Status | The seed typically undergoes a period of dormancy (rest) and requires external conditions (water, oxygen, temperature) to break it. | Dormancy is absent or very brief; growth begins immediately upon seed maturity. |
| Survival Strategy | Common strategy for survival, dispersal, and awaiting favorable environmental conditions. | A specialized adaptation, common in mangrove plants and certain fruits (like corn or tomatoes left on the vine too long), to ensure the seedling is robust enough for immediate establishment in harsh environments (e.g., salty mud). |
| Examples | Pea, Bean, Wheat, Maize. | Mangrove species (like Rhizophora), some varieties of corn or tomato. |
Question 6.
Justify the statement that the maize grain is a ‘one-seeded fruit’.
Ans:
The statement that the maize grain is a “one-seeded fruit” is justified because it meets the botanical definition of a fruit, yet contains only a single, inseparable seed.
Justification: The Maize Grain (Caryopsis)
1. It is a Fruit (Botanical Definition)
A fruit is defined as a mature, ripened ovary of a flower.
- The maize grain develops directly from the entire ovary of the female flower after fertilization. Therefore, based on its origin, it is technically a fruit.
2. It is ‘One-Seeded’
The maize kernel contains only one ovule, which develops into a single seed.
- Each kernel on the cob represents the entire output of one successful fertilization event of one female flower.
3. Key Feature: Fusion of Layers
The maize grain belongs to a specific type of fruit called a caryopsis (or grain), characteristic of the grass family.
- In a caryopsis, the fruit wall (pericarp) is permanently and completely fused with the underlying seed coat (testa). This fusion means the seed cannot be easily separated from the fruit wall.
- Because the two protective layers are inseparable, the entire structure is handled and eaten as one unit, which leads to the dual and confusing nature of the name.
Question 7.
What is the role played by the hypocotyl in epigeal germination?
Ans:
The hypocotyl plays the crucial role of elongation and lifting in epigeal germination.
Role of the Hypocotyl
- Elongation and Arch Formation: The hypocotyl (the region of the embryonic axis below the cotyledons) elongates rapidly. As it grows, it forms an arch (a hook shape) above the ground.
- Lifting Mechanism: This arch emerges from the soil first, pulling the cotyledons and the plumule (embryonic shoot) upward out of the soil. This lifting action is essential for epigeal germination.
- Cotyledon Exposure: Once the arch straightens out, the cotyledons are carried above the ground. This exposes the cotyledons to sunlight, where they turn green and begin photosynthesis until the true leaves of the plumule take over.
Question 8.
1. With regard to germination in bean seed, answer the following question:
State the function of the ‘micropyle’.
2. With regard to germination in bean seed, answer the following question:
Name the part of the seed that grows into the seedling.
3. With regard to germination in bean seed, answer the following question:
Draw a neat labelled diagram of the structure named above.
4. With regard to germination in bean seed, answer the following question:
Name the part of the seed that provides nutrition for the growing seedling.
Ans:
Here are the answers regarding germination in the bean seed:
1. Function of the Micropyle
The function of the micropyle is two-fold during germination:
- It acts as the primary opening through which the dry seed absorbs water (imbibition), initiating the germination process.
- It serves as the pore through which the seed obtains oxygen O2 necessary for respiration.
2. Part of the Seed that Grows into the Seedling
The part of the seed that grows into the seedling is the Embryo.
- The radicle (part of the embryo) grows into the root system.
- The plumule (part of the embryo) grows into the shoot system.
3. Diagram of the Embryo
The diagram of the embryo should include:
- Radicle (embryonic root)
- Plumule (embryonic shoot)
- Hypocotyl (embryonic stem below the cotyledons)
- Epicotyl (embryonic stem above the cotyledons)
- Cotyledons (seed leaves)
4. Part of the Seed that Provides Nutrition
The part of the bean seed that provides nutrition for the growing seedling is the Cotyledons.
- Bean seeds are non-endospermic (exalbuminous), meaning the food meant for the embryo was transferred to the two large, fleshy cotyledons during seed development.
