Video Transcript
The diagram provided shows a
simplified structure of a dicotyledonous plant stem. The pith occupies the center of the
stem and is comprised of parenchyma cells. What is the main purpose of the
pith? (A) To break down or destroy dead
plant cells, (B) to dissolve excess carbon dioxide, (C) to act as the site of
respiration, (D) to store and transport nutrients, or (E) to provide mechanical
support to the stem.
This question presents us with an
image showing a cross section of a dicotyledonous stem and asks us to identify the
main purpose of the pith. It’s worth noting that
monocotyledonous plant stems have a slightly different structure.
Let’s take a look at the structures
found within a dicotyledonous stem that have been labeled on the diagram and discuss
their functions.
The outermost layer of cells in the
plant stem and also in their leaves, roots, and flowers is called the epidermis. The epidermis forms a protective
boundary between the external environment and the plant’s inner tissues. Moving inward from the epidermis
are several layers of spongy tissues that make up a region called the cortex,
consisting of parenchyma and collenchyma tissues. The majority of the cortex is made
up of soft, fleshy parenchyma tissue. The cells in parenchyma tissues
have plenty of air spaces between them to promote gas exchange and chloroplasts to
carry out photosynthesis.
The collenchyma tissue in the
cortex is found directly below the epidermis of growing stems. Collenchyma cells have thickened,
reinforced cell walls to provide structural support and some flexibility to growing
regions of the plant.
We can also see several vascular
bundles in this diagram, which make up the plant’s transport system. One vascular bundle has been
circled in orange. Each vascular bundle contains
phloem tissue and xylem tissue. Phloem is responsible for
transporting sugars and amino acids up and down the plant stem, primarily from the
leaves, as this is where most of them are produced, to the different parts of the
plant that require them.
Xylem is responsible for
transporting water and some dissolved mineral ions up the stem from the roots to all
the other parts of the plant. The innermost region of the plant
stem consists of a spongy tissue called pith, which is composed of parenchyma
cells. The main function of the pith is to
store essential nutrients like water and sugars, which can be transported between
the pith and the vascular bundles.
This means that we have found the
main purpose of the pith and therefore the correct answer to this question. The main purpose of the pith is
(D): to store and transport nutrients.
