2.5 Plant growth and development

• Concept of growth and development
• Seed dormancy: causes and how to break it
• Conditions necessary for germination
• Types of germination: epigeal and hypogeal
• Primary and secondary growth
• Role of growth hormones

• explain the meaning of growth and development in plants
• describe the causes of seed dormancy
• determine the conditions necessary for germination
• differentiate between epigeal and hypogeal germination
• distinguish between primary and secondary growth
• describe the role of growth hormones
• appreciate the concept of growth and development in plants

“What brings about growth in plants?”

“Why does a seed not germinate the moment it lands on wet soil?”

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1. Dormancy and germination
   40 min · 2 practice tasks · quiz
   Why a seed waits, what finally wakes it, and the two ways a seedling emerges.
2. Primary and secondary growth, and plant hormones
   40 min · 2 practice tasks · quiz
   How a plant gets taller and thicker, and the chemicals that make a shoot bend towards light.
3. Growth versus development
   40 min · 1 practice tasks · quiz
   Getting bigger is not the same as getting more organised, and dry mass is the honest way to measure it.
4. Inside a germinating seed
   40 min · 1 practice tasks · quiz
   The parts of a seed, and the chemical sequence that turns a food store into a root and a shoot.
5. Why seeds stay dormant
   40 min · 1 practice tasks · quiz
   Dormancy is a refusal to germinate too soon, and Kenyan seeds use several tricks to wait.
6. Breaking dormancy in practice
   40 min · 1 practice tasks · quiz
   How farmers and foresters wake a waiting seed, matching the method to the cause.
7. The germination experiment
   40 min · 1 practice tasks · quiz
   Four tubes, one variable each, and why a flooded shamba behaves like the oil-covered tube.
8. Epigeal and hypogeal seedlings
   40 min · 1 practice tasks · quiz
   Which part elongates decides whether the seed leaves come up, and that matters to birds, weeds and planting depth.
9. Meristems and primary growth
   40 min · 1 practice tasks · quiz
   A plant gets longer only at its tips, and ink marks on a root show that stretching, not the tip itself, adds the centimetres.
10. Tropisms and hormone uses
    40 min · 1 practice tasks · quiz
    Uneven auxin makes a shoot lean to a window, and the same chemistry is sold as rooting powder and weedkiller.