Download Chapter 30.5

CHAPTER 30.5
How Do Organic Compounds Move Through
Plants?
AP Biology
Spring 2011
CONDUCTING TUBES IN PHLOEM

Phloem: living vascular tissue with organized
arrays of conducting tubes, fibers, and
parenchyma cells
CONDUCTING TUBES IN PHLOEM
Sieve tube cells: alive at
maturity and are
interconnected side by side
and end to end from the roots
to the leaves
 Companion cells: located
next to sieve tubes and
function to actively transport
the products of photosynthesis
into the sieve tubes

CONDUCTING TUBES IN PHLOEM

Carbohydrates are mainly stored as insoluble
starch molecules that must be converted to more
soluble carbohydrates

Such as sucrose before being transported throughout
the plant
TRANSLOCATION
Translocation: transport of sucrose and other
compounds through phloem
 Movement of molecules through phloem is from
sources to sinks

Source: mostly leaves
 Sink: flowers and fruits

TRANSLOCATION

Observations of plant-sucking insects
demonstrates that the sugary fluid in the phloem
is under high pressure
TRANSLOCATION

Pressure flow theory: translocation depends on
pressure gradients
Solutes are loaded by active transport into the
phloem from a source (ex. Leaves)
 Water enters by osmosis due to increase in solutes
 Pressure builds in sieve tubes pushing the sucroseladen fluid out of the source, into the stems, and on
the sink (ex. Fruit)
