Year 10 Biology: Plant Hormones and Hormonal Coordination

Introduction to Plant Hormones

Plants are amazing organisms that can adapt and grow in their environment. One of the ways they do this is through hormones. Plant hormones are special chemicals that help control how plants grow and respond to changes around them.

What are Plant Hormones?

Plant hormones are like tiny messengers in a plant. They travel through the plant and tell it what to do. Just like our hormones help us grow and feel different emotions, plant hormones help plants grow and respond to their environment.

Key Types of Plant Hormones

1. Auxins: These hormones help with growth, especially in stems and roots. They make the plant grow towards light (a process known as phototropism).
   • Example: If you place a plant near a window, auxins will cause the side of the plant that is away from the light to grow faster, making the plant lean towards the light.
2. Gibberellins: These hormones promote growth and help seeds germinate (start growing into new plants).
   • Example: When a seed absorbs water, gibberellins help it break out of its shell and grow into a plant.
3. Cytokinins: These hormones encourage cell division and help plants grow new tissues.
   • Example: Cytokinins are used in agriculture to keep cut flowers fresh for longer.
4. Abscisic Acid (ABA): This hormone helps plants deal with stress, like lack of water. It can slow down growth and cause leaves to fall off trees in autumn.
   • Example: During a drought, ABA will signal the plant to conserve water.
5. Ethylene: This hormone is a gas that helps fruits ripen and can also affect the growth of flowers.
   • Example: When you put bananas in a bag, the ethylene gas they release helps them ripen faster.

How Do Plant Hormones Work?

Plant hormones work by moving from one part of the plant to another. They interact with specific cells and tissues to trigger responses. This is called hormonal coordination.

Key Points about Hormonal Coordination

• Plant hormones work in very small amounts.
• They can have different effects depending on their concentration and the part of the plant they affect.
• Hormonal responses can be influenced by environmental factors such as light, temperature, and water availability.

Tips and Tricks to Remember Plant Hormones

• Mnemonic: Remember the main hormones using the phrase “A Good Cat And Elephant”:
  • Auxins
  • Gibberellins
  • Cytokinins
  • Abscisic Acid
  • Ethylene
• Visualising how hormones affect plant growth can help you understand their roles better. Draw diagrams showing how auxins help plants grow towards light.

Questions on Plant Hormones and Hormonal Coordination

Easy Level Questions

1. What are plant hormones?
2. Name one type of plant hormone.
3. What do auxins help plants do?
4. What is the role of gibberellins?
5. How do cytokinins help plants?
6. What does abscisic acid do during a drought?
7. What gas do ripening fruits release?
8. What is hormonal coordination?
9. Why are hormones important for plants?
10. Where do plant hormones travel to in a plant?
11. What happens to leaves in autumn due to hormones?
12. How do you think auxins affect plant growth?
13. What is one effect of ethylene gas?
14. What type of growth does gibberellins promote?
15. How can you keep cut flowers fresh longer?
16. What helps seeds germinate?
17. What happens when a plant is near a light source?
18. Name a factor that can influence plant hormones.
19. How do hormones affect cell division?
20. Why do plants need to respond to their environment?

Medium Level Questions

1. Explain how auxins work in phototropism.
2. Describe the role of gibberellins in seed germination.
3. How do cytokinins affect the growth of new tissues?
4. What is the impact of abscisic acid on a plant during water scarcity?
5. How do ethylene levels affect fruit ripening?
6. How do plant hormones differ from animal hormones?
7. Describe a situation where a plant might use abscisic acid.
8. What would happen if a plant produced too much auxin?
9. Explain the relationship between light and auxin distribution.
10. Why is it important for plants to have hormonal coordination?
11. How can farmers use plant hormones to improve crop production?
12. What happens to a plant that cannot produce gibberellins?
13. How does temperature affect plant hormones?
14. What is the role of auxins in root development?
15. Why might a plant need to slow down its growth?
16. How do hormones influence flowering in plants?
17. Describe an experiment to test the effect of light on auxin distribution.
18. What is the significance of ethylene in agriculture?
19. How do plant hormones work together to control growth?
20. Why do you think plants need hormones to survive?

Hard Level Questions

1. Discuss the mechanisms by which auxins promote cell elongation.
2. Explain the feedback loop between abscisic acid and water availability.
3. How do different concentrations of gibberellins affect plant growth?
4. Compare and contrast the roles of cytokinins and auxins.
5. How can knowledge of plant hormones lead to advancements in biotechnology?
6. What experiments could be conducted to observe the effects of ethylene on fruit ripening?
7. Explain how auxins and gibberellins work together during seedling growth.
8. Describe the role of hormones in the process of photoperiodism in plants.
9. How do hormonal signals integrate with environmental signals in plants?
10. Discuss the impact of synthetic plant hormones on agriculture.
11. Explain the process of apical dominance and the role of auxins.
12. How do environmental stressors alter hormone production in plants?
13. Describe how cytokinins can delay leaf senescence.
14. How do you think changes in climate could affect plant hormonal responses?
15. Discuss the physiological effects of ethylene on flower development.
16. What role do plant hormones play in the process of fruit development?
17. How do hormones influence the timing of flowering in response to season?
18. Explain how auxins could be used in rooting powders.
19. Discuss the role of plant hormones in agricultural pest resistance.
20. How has research on plant hormones influenced sustainable farming practices?

Answers and Explanations

Easy Level Answers

1. Plant hormones are special chemicals that help control plant growth and responses.
2. Auxins.
3. Auxins help plants grow towards light.
4. Gibberellins help seeds start growing.
5. Cytokinins help plants grow new tissues by encouraging cell division.
6. Abscisic acid helps plants conserve water.
7. Ethylene gas helps fruits ripen.
8. Hormonal coordination is how plant hormones work together to control growth.
9. Hormones are important for plants because they help them adapt and grow.
10. Plant hormones travel through the plant from one part to another.
11. Leaves fall off trees in autumn due to abscisic acid.
12. Auxins make the plant grow towards light.
13. Ethylene gas makes fruits ripen faster.
14. Gibberellins promote vertical growth.
15. You can keep cut flowers fresh longer by using cytokinins.
16. Gibberellins help seeds germinate.
17. The plant bends towards the light because of auxin distribution.
18. Light can affect how much auxin is produced.
19. Hormones affect cell division by signaling cells to divide.
20. Plants need to respond to their environment for survival and growth.

Medium Level Answers

1. Auxins move to the side of the plant away from light, causing that side to grow longer and the plant to bend towards the light.
2. Gibberellins break down starches in seeds and trigger growth.
3. Cytokinins promote cell division and help create new shoots and roots.
4. Abscisic acid causes stomata to close, helping the plant conserve water.
5. Ethylene promotes ripening and can cause other fruits to ripen faster.
6. Plant hormones are produced in different ways and serve different functions, reflecting the needs of plants versus animals.
7. A plant might produce abscisic acid in response to dry soil to prevent water loss.
8. Too much auxin could lead to uncontrolled growth or deformities.
9. Light causes auxin to be distributed unevenly, leading to growth towards the light.
10. Hormonal coordination ensures that plants grow properly and respond effectively to changes.
11. Farmers can use hormones to promote flowering or fruiting in crops.
12. Without gibberellins, seeds may not germinate or grow properly.
13. Temperature can influence hormone production, affecting growth rates.
14. Auxins help roots grow down into the soil, anchoring the plant.
15. Plants slow growth to conserve energy and resources when conditions are not ideal.
16. Hormones control when flowers bloom based on environmental cues.
17. You could use a light source and measure plant growth in different light conditions.
18. Ethylene can be used to control the ripening of fruits for shipping and selling.
19. Hormones work together to allow plants to grow, respond to light, and adapt to their environment.
20. Plants need hormones for growth, reproduction, and to respond to threats like pests.

Hard Level Answers

1. Auxins promote cell elongation by weakening cell walls, allowing them to stretch and grow.
2. When water is scarce, abscisic acid signals the plant to close stomata, reducing water loss.
3. Higher concentrations of gibberellins can lead to taller plants, while lower concentrations may have less effect.
4. Cytokinins promote cell division, while auxins help with elongation; both are essential for balanced growth.
5. Understanding plant hormones can lead to better crop management and improved yields.
6. You can observe changes in color and texture of fruits in response to ethylene treatment.
7. Auxins encourage upward growth, while gibberellins help with overall height and vigor.
8. Hormones help plants sense day length and trigger flowering at the right time.
9. Plants integrate hormonal and environmental signals to grow effectively and survive.
10. Synthetic hormones can enhance growth, but they can also disrupt natural ecosystems if used improperly.
11. Auxins inhibit the growth of lateral buds, allowing the main shoot to grow taller.
12. Environmental factors like drought change hormone levels to help plants adapt.
13. Cytokinins can delay leaf aging, keeping them green and functional longer.
14. Changes in climate may lead to altered hormone responses, affecting growth and reproduction.
15. Ethylene can cause flowers to open and become more attractive to pollinators.
16. Hormones like auxins and gibberellins play crucial roles in fruit size and quality.
17. Hormones respond to changes in light and temperature, influencing flowering time.
18. Auxins in rooting powders stimulate root growth in cuttings.
19. Some plant hormones can trigger defenses against pests, improving survival rates.
20. Research into plant hormones helps develop practices that are both productive and environmentally friendly.

By understanding the roles of plant hormones and their coordination, you’ll see how essential they are for plant life and agriculture!