Video Transcript
Which two tissues, involved in
transport, make up the vascular bundle in plant stems? (A) Xylem and pith, (B) parenchyma
and epidermis, (C) phloem and cortex, or (D) xylem and phloem.
This question asks us to identify
the two tissues, which are involved in transport, that make up the vascular bundle
in plant stems. Let’s take a look at some of the
structures found within a typical dicot stem and discuss their functions. It’s worth noting that monocot
plant stems have a slightly different structure.
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 plant’s inner tissues and the external environment.
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 and are of
interest to us in this question. 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 will be 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.
This means that we have found the
tissues involved in transport that make up the vascular bundle in plant stems and,
therefore, the correct answer to this question. The two tissues that make up the
vascular bundles are (D) xylem and phloem.
