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Leaving Cert Biology Revision: Plant Responses & Seed Growth

Plant Responses & Seed Growth


Vegetative Propagation in Flowering Plants


Vegetative propagation, a form of asexual reproduction, occurs naturally in many flowering plants through various methods. 




These natural methods ensure the survival and spread of plant species with no seeds. Here are some examples:


1. Runners (Stolons):


  •  Some plants, like strawberries and spiders, produce long, slender stems above the ground called runners or stolons.

  •  These runners grow horizontally and produce new plants at nodes where they come in contact with soil.


Example


Spider plant (Chlorophytum comosum) produces runners that grow baby spider plants, known as offsets, at their ends.




2. Rhizomes:


  •    Rhizomes are underground horizontal stems that grow beneath the soil surface.

  •     Nodes along the rhizome give rise to new shoots and roots, allowing the plant to spread.

  •     Example: Ginger (Zingiber officinal) grows from rhizomes, which produce new shoots and roots as they spread horizontally underground.



3. Suckers:


  • Suckers are new shoots that emerge from the base of a plant's stem or its roots.

  • They grow into independent plants, often forming clumps or colonies of genetically identical individuals.


Example


Blackberry (Rubus fruticose's) plants produce suckers that develop into new plants, helping the species spread.





4. Offsets:


  •   Offsets are small, genetically identical plants that develop alongside the parent plant.

  •   They often arise from the base of the parent plant and eventually become independent individuals.


Example


Aloe vera (Aloe barbadensis) produces offsets, or "pups," that grow at the base of the main plant and can be separated to form new plants.



5. Bulbils:


  • Some flowering plants produce small, bulb-like structures called bulbils on their stems or leaves.

  • These bulbils develop into new plants when they fall to the ground or are dispersed by animals.


Example


Garlic (Allium sativum) produces bulbils on its flower stalk, which can sprout into new garlic plants when they land on suitable soil.



6. Tubers:


  •    It has swollen underground stems that store nutrients.

  •    Example: Potatoes.

  •    Eyes or buds on the tuber can grow into new plants.



7. Corms:


  •    Short, vertical, swollen underground stems.

  •    Example: Crocus.

  •    New corms form around the base of the old one.




8. Cuttings:


  •    Pieces of stems, leaves, or roots cut from the parent plant.

  •    They were placed in soil or water to grow new roots and shoots.


Example


Many houseplants like pothos or coleus.


7. Layering:


  •    Stems are bent to the ground and covered with soil.

  •    Roots form at the covered part, and the stem can be cut to create a new plant.



Advantages of Vegetative Propagation


Quick Growth


 New plants can grow faster than from seeds.


Clone Plants


 Offspring are genetically identical to the parent, ensuring desirable traits are passed on.


No Seed Needed


 Useful for plants that don't produce viable seeds or take a long time to germinate.


Resilience


 Vegetatively propagated plants can be hardier, as they are exact replicas of a proven, mature plant.





Examples in Everyday Life


  1. Gardening: Many gardeners use cuttings or layering to propagate favorite plants.


  1. Agriculture: Farmers propagate crops like potatoes and strawberries to ensure consistent quality and yield.


  1. Horticulture: Florists propagate flowers like tulips and lilies using bulbs and corms to meet high demand.


Seed Growth


1. Germination


  • The start of a seed turns into a plant.

  • Needs water, oxygen, and the right temperature.


2. Stages of Germination


  1. Imbibition


  • Seed takes in water and swells.

  • Activates enzymes needed for growth.


  1. Radicle Emergence


  • The first root breaks out of the seed.

  • Grows downward to anchor the plant and absorb water.


  1. Shoot Emergence

 

  • The first shoot appears and grows upward.

  • Begins photosynthesis to produce food for the plant.


3. Factors Affecting Seed Growth


  1. Water


  • Essential for seed swelling and activating growth processes.


  1. Temperature


  • Seeds need a certain temperature range to germinate.

  • Too cold or too hot can stop growth.


  1. Light Some seeds need light to start growing, while others grow better in the dark.


  1. Soil Quality

 

  • Nutrient-rich soil helps seeds grow into strong plants.


4. Seedling Development


  1. Primary Leaves


  • The first leaves to grow after germination.

  • Start making food through photosynthesis.


  1. Root Development

 

  • Roots grow and spread out to anchor the plant and take in water and nutrients.


  1. Stem Growth

 

  • The stem gets longer, helping the plant stand upright and transport nutrients and water.


  1. Leaf Expansion

  • More leaves grow, increasing the plant's ability to make food.

  • Helps the plant grow faster and stronger.

Importance of Natural Vegetative Propagation


Genetic Continuity 


Natural vegetative propagation ensures the perpetuation of specific genetic traits within plant populations.


Rapid Colonization


Plants that propagate vegetatively can rapidly colonize new habitats and expand their range.


Adaptation to Environment


Vegetative propagation allows plants to adapt to local environmental conditions, promoting survival and success in diverse ecosystems.


Natural methods of vegetative propagation play a vital role in the reproduction and dispersal of flowering plants, contributing to the biodiversity and resilience of ecosystems.





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