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Transport in Plants - Coggle Diagram
Transport in Plants
Transpiration
Transpiration is the process by which water vapor is lost from leaves. It is essential for regulating plant temperature and water balance. Here's how it works:
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Transpiration Pull
Transpiration pull is a mechanism by which water is drawn up the xylem in plants. As water evaporates from the leaves, it creates a tension in the xylem that pulls water molecules up from the roots. This tension is due to the cohesive forces between water molecules, which attract each other.
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Wilting
Wilting is the visible drooping or curling of leaves that occurs when water loss exceeds water uptake. When a plant wilts, it is losing turgor pressure, which is the pressure that keeps plant cells rigid. This can happen due to a lack of water availability or excessive transpiration.
Humidity: Lower humidity creates a greater vapor pressure deficit between the leaves and the surrounding air, promoting transpiration.
Wind speed: Higher wind speeds remove water vapor from around the leaves, increasing the diffusion rate and transpiration rate.
Temperature: Higher temperatures increase the rate of evaporation, which leads to increased transpiration.
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Xylem and Phloem
xylem – transport of water and mineral ions, and support
phloem – transport of sucrose and amino acids
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The structure of xylem vessels is directly related to their function of transporting water and providing support. Here are some key features:
Thick walls with lignin: Lignin is a strong, woody material that strengthens the cell walls and helps to prevent them from collapsing under the pressure of water transport.
No cell contents: Mature xylem vessels are dead cells with no cytoplasm or nucleus. This allows for unobstructed water flow.
End-to-end connections with no cross walls: Xylem vessels are made up of long, hollow tubes joined end-to-end. The absence of cross walls creates a continuous pathway for water transport.
Water Uptake
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Root hair cells are microscopic extensions of root epidermal cells that significantly increase the surface area for water and mineral ion absorption. They are located in the root hair zone, which is the region just behind the root tip.
Mesophyll cells: Finally, water reaches the mesophyll cells in the leaves, where it is used for photosynthesis and other plant functions.
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Root cortex cells: From the root hair cells, water travels through the root cortex cells.
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Translocation
Translocation is the movement of organic substances, primarily sucrose and amino acids, within a plant. This process occurs through the phloem, a specialized tissue that transports these nutrients from areas of abundance (sources) to areas of need (sinks).
Sources are parts of a plant that produce or release sucrose or amino acids. Typically, these are areas undergoing photosynthesis, such as mature leaves. Other sources include storage organs, like bulbs or tubers, during periods when they are breaking down their reserves.
Sinks are parts of a plant that utilize or store sucrose and amino acids. Examples of sinks include:
Growing regions: Meristems, young leaves, and developing fruits.
Storage organs: Roots, tubers, and bulbs during periods of active growth.
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It's important to note that the roles of source and sink can change depending on the plant's stage of development and environmental conditions.
A storage organ (like a potato tuber) can act as a sink during the growing season when it's accumulating carbohydrates.
However, the same storage organ can become a source during the following spring when it breaks down its starch reserves to support new growth.
This dynamic nature of source-sink relationships ensures the efficient distribution of resources within the plant.
