Video Transcript
Functionally, a plant can be
divided into sources and sinks. Which parts of the plant are
sources of sugars? (A) Anywhere sugars are stored,
e.g., the seeds, or (B) anywhere sugars are made, e.g., the leaves.
Let’s start by reviewing some of
the key terms that are relevant to this question.
Translocation is the movement of
sucrose in a plant. Let’s review where this sucrose
comes from in the first place. Photosynthesis is the process by
which plants use light energy to convert carbon dioxide and water into oxygen and
glucose, which is a type of sugar. Glucose provides an energy source
for the plant, as it can be broken down in cellular respiration. However, you might recall that
translocation moves sucrose around the plant and not glucose.
Plants combine glucose with another
sugar called fructose to form sucrose. This process is important, as
sucrose won’t react with oxygen in cellular respiration as it is translocated like
glucose would. The places in a plant where these
photosynthetic products like glucose are made are called sources. For example, the leaves and stems
of plants are typically sources, as this is where most photosynthesis will
occur.
The products themselves are called
assimilates, and they are moved through specialized tissues called phloem to target
locations that require the sugars for cellular respiration to release energy. These locations to which sugars are
moved are called sinks. Some examples of sinks are roots,
seeds, and developing fruits. They are regions that require
sugars as they need a lot of energy to function.
If we take a look back at the
question, we are being asked which parts of the plant are sources of sugars. We now know that a source of sugars
in a plant is (B), anywhere sugars are made, e.g., the leaves.
