PHOTOSYNTHATES ARE TRANSPORTEDTHROUGH PHLOEM BY SYMPLASTIC OR APOPLASTIC TRANSPORT SYSTEMS. GIVE A CHARACTERIZATION OF THE TWO TRANSPORT SYSTEM.
The symplastic and apoplastic transport systems are two different pathways by which photosynthates (products of photosynthesis) are transported through the phloem in plants.
1. Symplastic Transport System:
- In the symplastic pathway, photosynthates move via the cytoplasmic continuum, which includes plasmodesmata, tiny channels connecting neighboring cells.
- Once photosynthates are produced in the mesophyll cells of the leaf, they enter the symplast and pass through plasmodesmata to neighboring cells.
- This transport system involves movement through the living cells, particularly the cytoplasm.
- The symplastic pathway is generally considered to be slower but more controlled, as all molecules must pass through living cells before reaching the phloem.
2. Apoplastic Transport System:
- In the apoplastic pathway, photosynthates move through the non-living spaces outside the cells.
- The transport occurs through the cell walls and extracellular spaces of plant tissues.
- Photosynthates can move freely between adjacent cells without crossing cell membranes.
- The apoplastic pathway is generally considered to be faster but less regulated compared to the symplastic pathway.
In conclusion, the symplastic transport system involves movement through the living cells of plants via plasmodesmata, while the apoplastic transport system involves movement through non-living spaces and the cell walls. Both systems play important roles in transporting photosynthates from the site of production (such as leaves) to the rest of the plant.
The symplastic and apoplastic transport systems are two mechanisms by which photosynthates (products of photosynthesis, such as sugars) are transported through the phloem in plants. Here's a characterization of each transport system:
1. Symplastic Transport System:
- In the symplastic transport system, photosynthates pass through the continuous cytoplasmic connections called plasmodesmata between adjacent cells.
- It involves movement of photosynthates from cell to cell, mainly through the interconnected cytoplasmic channels.
- This transport system utilizes the symplast, which refers to the interconnected cytoplasmic continuum present in plant cells.
- The photosynthates enter one cell and move through plasmodesmata into neighboring cells until they reach the phloem sieve tubes for long-distance transport.
- It allows for selective regulation and communication between cells, as they share their metabolic processes via the plasmodesmata.
2. Apoplastic Transport System:
- In the apoplastic transport system, photosynthates move through the non-living extracellular spaces outside the cell membranes.
- It involves transport through the cell walls and extracellular spaces, bypassing the cytoplasm of the cells.
- The photosynthates are carried along the apoplast, which refers to the interconnected spaces within the cell walls of plant tissues.
- In this transport mechanism, the photosynthates are taken up by the apoplast of one cell and travel through cell walls to reach adjacent cells.
- At certain checkpoints, like the endodermis in the roots or the bundle sheath cells in leaves, the photosynthates need to cross the plasma membranes before entering the symplast for further transport through the phloem.
Both transport systems play important roles in the translocation of photosynthates throughout the plant. The symplastic transport system allows for more controlled and regulated movement between cells, while the apoplastic transport system allows for faster movement through extracellular spaces. The exact dominance of each system may vary depending on plant species, tissue types, and environmental conditions.
The symplastic and apoplastic transport systems are two mechanisms involved in the movement of photosynthates (sugars) through the phloem in plants. Here are their characteristics:
1. Symplastic Transport System:
- In the symplastic transport system, photosynthates move through the symplast, which includes the interconnected cytoplasm of plant cells through plasmodesmata (small channels between adjacent cells).
- This transport pathway involves the movement of molecules through the living parts of the plant, such as living cells.
- Symplastic transport is highly selective and regulated, allowing for controlled movement of photosynthates.
- This transport system maintains the integrity of cells and ensures that the movement of photosynthates is under the cellular control.
2. Apoplastic Transport System:
- The apoplastic transport system involves the movement of photosynthates through the non-living spaces outside of the living cells, such as cell walls, intercellular spaces, and the xylem.
- Photosynthates can freely move through the apoplast without encountering living cell membranes.
- This transport pathway allows for faster movement of molecules due to the absence of cellular barriers.
- Unlike symplastic transport, apoplastic transport does not involve the direct regulation of cellular processes.
It's important to note that both symplastic and apoplastic transport systems can occur simultaneously in plant tissues, and the relative contributions of each can vary depending on different factors like plant species, tissue types, and environmental conditions.