Video Transcript
The diagram provided shows a
simplified structure of a dicotyledonous plant stem. What structure is indicated by the
question mark? (A) Epidermis, (B) cortex, (C)
pith, or (D) vascular bundle.
This diagram shows us a cross
section of a dicot stem. And we need to identify one of the
structures within it. To do this, let’s look at the dicot
stem structures that are mentioned in these answer options.
The epidermis is a single layer of
cells around the plant stem that forms a boundary to the external environment,
acting as a tough skin for the plant. The epidermis often produces a waxy
cuticle to coat it that can protect the stem from mechanical damage or water loss
and may help prevent the entrance of dangerous microorganisms that may cause
infection.
Just below the epidermis are
several layers of cells that make up a region called the cortex. The cortex is a spongy region made
up of many simple tissues, such as parenchyma tissues, and in growing stems
collenchyma tissues, right below the epidermis. While parenchyma cells make up a
lot of the soft fleshy tissues within various parts of the plant, collenchyma cells
provide some structure and flexibility to growing stems.
Pith is a spongy tissue found in
the center of dicot stems. Pith is also mainly made up of
parenchyma cells, as its primary function is storage of substances like water and
sugars.
The question mark is pointing to a
structure called a vascular bundle. The vascular bundles are the
plant’s transport systems, which move essential nutrients, like water and sugars,
around the plant to the different organs that require them. Around the exterior of each
vascular bundle is a tough region of sclerenchyma tissues, which helps to support
the vascular bundle. The vascular bundle also includes
phloem tissues, which transport sugars and amino acids around the plant, and has
been shown in this diagram in blue.
Moving closer to the pith, the
vascular bundle also contains xylem tissues. Xylem is responsible for
transporting water and dissolved mineral ions from the roots of the plant to the
other parts that require them. It’s shown in this diagram in
red. Therefore, the structure that was
marked with a question mark in this diagram was the vascular bundle.
