Correct option is A
In plants, phloem transport is responsible for the long-distance movement of photo-assimilated carbon, primarily in the form of sugars. The sugars that are transported in the phloem must be effective in terms of solubility, stability, and ease of movement.
Reducing sugars (like glucose and fructose) are not ideal for long-distance phloem transport because they are chemically reactive and can lead to the formation of unwanted byproducts through reactions like Maillard reactions or oxidation. These sugars can also cause osmotic imbalances, which can affect the efficient movement of water and solutes in the plant.
Mannitol (Option 2) is a non-reducing sugar alcohol that is widely used by certain plants for phloem transport. It is stable and does not undergo oxidation, making it well-suited for long-distance transport.
Galactosyl-sucrose oligosaccharides (Option 3) are oligosaccharides that combine galactose and sucrose. These are common forms of sugars transported in the phloem, as they are stable and less reactive compared to reducing sugars.
Non-reducing sugars (Option 4), like sucrose, are the primary sugars used for phloem transport because they are stable, non-reactive, and do not interfere with the plant’s transport systems.
Therefore, reducing sugars are least suited for long-distance phloem transport due to their chemical reactivity and potential to cause unwanted side reactions.
Information Booster:
Phloem Transport: The phloem in plants is responsible for moving organic nutrients, primarily sugars produced during photosynthesis (photo-assimilates), from sources (like leaves) to sinks (like roots and fruits). The efficient transport of these sugars is crucial for plant growth and development.
Role of Sugars in Phloem: Sugars like sucrose are the primary carriers of carbon in the plant’s phloem. Non-reducing sugars like sucrose are favored because they are stable, less likely to undergo undesirable chemical reactions, and maintain osmotic balance, which is vital for water movement.
Reducing Sugars: Reducing sugars have a free aldehyde or ketone group that makes them chemically reactive. They are less stable in solution, and their reactivity can interfere with the plant's transport system, making them unsuitable for long-distance movement.
Mannitol: Although not commonly used in all plants, mannitol is a sugar alcohol that is stable and effective for long-distance transport in certain species, such as some members of the Apiaceae family (carrot family).
Galactosyl-sucrose Oligosaccharides: These oligosaccharides are stable and well-suited for transport, especially in certain plant species that may use them for storage and transport of sugars over long distances.
