Correct option is D
In plants, phloem translocation refers to the movement of sugars (mainly sucrose) and other organic nutrients from a "source" (where they are produced or stored) to a "sink" (where they are consumed or stored).
- Mature leaves act as the predominant source organ because they undergo photosynthesis, producing carbohydrates that are then transported to different parts of the plant.
- Roots, developing fruits, and immature leaves function as sink organs because they require energy and nutrients for growth and development.
Information Booster
- Source-Sink Relationship: In plants, sources produce and supply sugars, while sinks consume or store them. This relationship changes during different growth stages.
- Major Source Organs: In most plants, mature leaves serve as the primary source of sucrose and other photosynthates.
- Major Sink Organs: Roots, young leaves, developing fruits, seeds, and storage organs (e.g., tubers, bulbs) are typical sinks.
- Phloem Loading: Mature leaves load sucrose into sieve tube elements via active transport, creating a pressure gradient for flow.
- Pressure Flow Hypothesis: Sugars move from sources to sinks due to pressure differences created by active loading at the source and unloading at the sink.
- Seasonal Changes: In some plants, storage organs (e.g., tubers) act as sources during early growth phases when leaves are not yet mature.
- Reversal of Source-Sink Roles: In plants like potatoes, underground storage organs act as sources during sprouting, supplying stored nutrients to growing shoots.
