Problem 4 - Biology of Aging

Question

Programmed leaf senescence results in a decrease in sucrose concentration in phloem. Does this observation reflect a decrease in the synthesis of intracellular glucose and fructose because of the decline in photosynthesis? Explain.

Step-by-Step Solution

Answer

Yes, the decrease in sucrose concentration in the phloem during leaf senescence reflects a decrease in the synthesis of intracellular glucose and fructose due to a decline in photosynthesis.

Step 1: Understand leaf senescence

Leaf senescence is a programmed development process in plants that usually occurs before leaf drop. It's marked by breakdown of chlorophyll, leading to decrease in photosynthesis.

Step 2: Relationship between photosynthesis and glucose/fructose synthesis

Photosynthesis in plants generates glucose, which can be converted to other sugars like fructose. Therefore, a decline in photosynthesis due to leaf senescence would lead to decrease in glucose and fructose synthesis.

Step 3: Understand sucrose and phloem connection

Plants transport glucose and fructose through the phloem in the form of sucrose, which is the primary sugar transported in most plants.

Step 4: Combining the understandings

As leaf senescence leads to decrease in photosynthesis, this will reduce glucose and fructose synthesis. The lower the glucose and fructose quantity, the less sucrose will be available to be transported in the phloem. This therefore leads to a lower concentration of sucrose in the phloem during leaf senescence.