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Question Video: Recalling the Types of Plant Tissues Found in the Cortex Biology

The diagram provided shows a simplified structure of a dicotyledonous plant stem. Which two types of plant tissue make up the stem cortex?


Video Transcript

The diagram provided shows a simplified structure of a dicotyledonous plant stem. Which two types of plant tissue make up the stem cortex? (A) Phloem and xylem, (B) parenchyma and collenchyma, (C) parenchyma and pith, or (D) collenchyma and epidermis.

This question is asking specifically about tissues in the cortex of the stem of dicotyledonous plants, sometimes called dicotyledons or dicots for short. It’s important to note that the stem structure of monocots is slightly different, but as this question is focusing on the stem structure of dicots, let’s dive right in.

The epidermis is an outer, protective, single layer of cells that sometimes produces a waxy cuticle to further protect the stem from physical damage. The waxy cuticle also helps reduce water loss and protect the plant from the entrance of pathogens. The cortex is found just inside the epidermis, and it is made up of several layers of simple tissues: parenchyma and collenchyma.

Simple tissues are made up of very similar cells that work together to carry out a particular role. Parenchyma cells make up the majority of the soft, spongy tissues within a plant, which are well adapted for gas exchange due to the air spaces surrounding them. Parenchyma cells usually contain many chloroplasts, as another one of their functions is to carry out photosynthesis.

Collenchyma cells are longer than parenchyma cells. They are also harder as the cell walls are reinforced with pectin, which helps them to provide structure. Collenchyma cells also usually contain chloroplasts for photosynthesis. These cells are often found just below the epidermis of the stem and are very important in the growing regions of plants to provide some support and flexibility.

The vascular bundles, one of which has been circled in orange, make up the transport system of a plant. They are composed of two main tissues: phloem and xylem. The phloem transports sugars and amino acids both up and down the stem to wherever they are needed in the plant. The xylem transports water and dissolved mineral ions up the plant stem from the roots to the leaves. In the center of the stem is the pith, which is made of spongy parenchyma tissue and is used for storage.

Now that we’ve reviewed many of the basic components of dicot stems, let’s return to the question, which asks us which two types of plant tissue make up the stem cortex. We can narrow down the answers from what we now know. The epidermis is found around the outside of the stem and forms an outer skin around the cortex but is not part of the cortex itself, so we can rule out option (D), collenchyma and epidermis. The vascular bundles, which are the transport system in plants, are made up of xylem and phloem, so we can rule out option (A), phloem and xylem. The pith is found in the center of the plant, while the cortex is located just under the epidermis, so we can rule out (C), parenchyma and pith.

Now we know the correct answer. The cortex of a dicot stem is made up of (B) parenchyma and collenchyma.

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