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Which of the following statements about phloem transport is correct?
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- phloem transport occurs unidirectionally
- gravity influences phloem transport
- Ca+ is the most abundantcation in phloem sap
- sugar is transported in phloem as non-reducing sugar
- phloem transport occurs unidirectionally
Correct Option: D
According to most textbooks, only non-reducing carbohydrate species such as sucrose, sugar alcohols, and raffinose-family sugars function as phloem translocates. In non-reducing sugar, the hydroxyl group on the anomeric carbon, the number one carbon, is tied up which means that they are less reactive and more chemically stable. Exclusive transport of non-reducing sugars probably reflects packaging of carbohydrate in a chemical form which protects it from being metabolized.
