1. Define seed germination and explain its significance.
Answer:
Seed germination is the process by which a dormant seed begins to grow and develop into a new plant under favorable environmental conditions. The seed absorbs water, activates metabolic processes, and the embryonic plant inside begins to grow. Germination is significant because it is the initial step in a plant’s life cycle, enabling the propagation of species, ensuring genetic diversity, and sustaining ecosystems and agriculture.
2. Describe the stages of seed germination.
Answer:
The stages of seed germination are:
- Imbibition: The seed absorbs water, swelling and softening the seed coat.
- Enzyme Activation: Water activates enzymes that break down stored food into energy.
- Respiration: The embryo undergoes aerobic respiration to generate ATP.
- Radicle Emergence: The radicle, the embryonic root, emerges, anchoring the seed.
- Plumule Growth: The plumule, the embryonic shoot, grows towards the light.
- Seedling Development: The seedling grows, developing true leaves for photosynthesis.
3. What are the factors affecting seed germination?
Answer:
The factors affecting seed germination include:
- Water: Essential for imbibition and enzyme activation.
- Oxygen: Required for aerobic respiration.
- Temperature: Optimal range varies with species; influences enzymatic activity.
- Light/Darkness: Some seeds need specific light conditions (e.g., lettuce requires light).
- Seed Dormancy: Overcoming dormancy through scarification, stratification, or hormonal treatment is crucial.
4. Explain the role of water in seed germination.
Answer:
Water is critical for seed germination as it facilitates:
- Imbibition: Initiates germination by hydrating the seed tissues.
- Enzyme Activation: Activates hydrolytic enzymes that mobilize stored nutrients.
- Metabolic Processes: Drives respiration and cell division.
- Growth: Softens the seed coat, allowing radicle and plumule emergence.
5. Discuss the role of temperature in seed germination.
Answer:
Temperature affects seed germination by influencing enzyme activity, membrane permeability, and metabolic rates. Each species has an optimal temperature range for germination. High temperatures may denature enzymes, while low temperatures can slow metabolic activity. Seeds of certain species (e.g., alpine plants) require cold stratification to break dormancy.
6. What is seed dormancy? How is it overcome?
Answer:
Seed dormancy is a state in which seeds do not germinate despite favorable conditions. It ensures survival during adverse conditions. Dormancy can be overcome by:
- Scarification: Mechanically breaking the seed coat.
- Stratification: Exposing seeds to cold, moist conditions.
- Chemical Treatments: Using gibberellins or removing inhibitors like abscisic acid.
- Light Exposure: For photoblastic seeds, providing appropriate light conditions.
7. Differentiate between epigeal and hypogeal germination.
Answer:
- Epigeal Germination: Cotyledons rise above the soil (e.g., beans).
- Hypogeal Germination: Cotyledons remain below the soil (e.g., maize).
Key differences include the position of cotyledons and the energy source for the growing seedling.
8. Describe the role of oxygen in seed germination.
Answer:
Oxygen is vital for aerobic respiration, which provides energy for cell division and growth during germination. In waterlogged soils, seeds may fail to germinate due to insufficient oxygen. Oxygen enters the seed through the micropyle and is utilized in the mitochondria to produce ATP.
9. How do enzymes contribute to seed germination?
Answer:
Enzymes play a pivotal role by catalyzing the breakdown of stored food reserves:
- Amylase: Converts starch to sugars.
- Protease: Breaks down proteins into amino acids.
- Lipase: Converts fats into fatty acids and glycerol.
These products provide energy and building blocks for growth.
10. What is vivipary? Explain with examples.
Answer:
Vivipary is a type of germination where seeds germinate while still attached to the parent plant. It typically occurs in mangroves (e.g., Rhizophora), enabling seedlings to anchor in the muddy environment immediately after detachment.
11. Explain the significance of the radicle and plumule during germination.
Answer:
- Radicle: The embryonic root that anchors the seedling and absorbs water and nutrients.
- Plumule: The embryonic shoot that grows upwards, eventually forming leaves for photosynthesis. Both are critical for establishing the seedling.
12. What are the physiological changes during seed germination?
Answer:
Physiological changes include:
- Water Uptake: Imbibition hydrates seed tissues.
- Enzyme Activation: Hydrolytic enzymes mobilize nutrients.
- Respiration: Increased oxygen uptake for ATP production.
- Cell Division and Elongation: Growth of radicle and plumule.
- Protein Synthesis: Required for cellular functions.
13. Discuss the role of gibberellins in seed germination.
Answer:
Gibberellins break seed dormancy and promote germination by:
- Activating enzymes like amylase.
- Mobilizing stored nutrients.
- Stimulating cell division and elongation in the embryo.
14. How does light influence seed germination?
Answer:
Light acts as a signal for photoblastic seeds. Positive photoblastic seeds (e.g., lettuce) require light to germinate, while negative photoblastic seeds (e.g., onion) germinate in darkness. Phytochromes mediate these light-dependent responses.
15. Why do some seeds fail to germinate even under favorable conditions?
Answer:
Seeds may fail to germinate due to:
- Dormancy: Requires specific treatments to break.
- Poor Viability: Aged or damaged seeds.
- Pathogens: Fungal or bacterial infections.
- Suboptimal Factors: Incorrect temperature, oxygen, or water levels.
16. What is scarification, and why is it important?
Answer:
Scarification is the process of mechanically or chemically breaking the seed coat to allow water and oxygen to penetrate. It is crucial for seeds with hard coats, such as legumes, to overcome physical dormancy.
17. Explain the energy dynamics during seed germination.
Answer:
Stored food reserves in the seed (starch, proteins, fats) are hydrolyzed into sugars, amino acids, and fatty acids. These are metabolized through cellular respiration to generate ATP, powering the growth of the embryo.
18. What are the environmental factors that affect seed germination?
Answer:
Key environmental factors include:
- Water: For imbibition and enzyme activation.
- Oxygen: For aerobic respiration.
- Temperature: Affects enzymatic activity.
- Light: Necessary for photoblastic seeds.
- Soil Conditions: pH and salinity can impact germination.
19. Describe the differences in seed germination between monocots and dicots.
Answer:
- Monocots: One cotyledon; coleoptile protects the shoot; endosperm is the main food source (e.g., maize).
- Dicots: Two cotyledons; radicle and plumule are exposed (e.g., beans).
20. Why is seed germination important in agriculture?
Answer:
Seed germination ensures the propagation of crops, aiding in food production, maintaining genetic diversity, and enabling the use of improved seed varieties for better yields and disease resistance.
