Chapter 44: Problem 6

Diagram the internal structure of a dicot stem after primary growth, labeling and describing the function of the epidermis, cortex, pith, xylem, and phloem. How does the structure change after secondary growth?

Short Answer

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After primary growth in a dicot stem, the internal structure consists of concentric layers - the central pith, surrounded by xylem, phloem, cortex, and epidermis. The epidermis protects the stem, the cortex provides support and storage, the pith stores food and water, the xylem transports water and minerals, and the phloem transports sugars. During secondary growth, radial expansion occurs due to the formation of secondary xylem and phloem by the vascular cambium, leading to a thicker and stronger stem. The cortex and epidermis are typically replaced by the protective periderm tissue.

Step by step solution

Diagram the internal structure of a dicot stem after primary growth.

Draw a cross section of a dicot stem after primary growth. In this drawing, label the different layers, including the epidermis, cortex, pith, xylem, and phloem. These layers will be situated in concentric circles with the pith at the center, surrounded by xylem, phloem, cortex, and epidermis respectively.

Describe the function of the epidermis.

The epidermis is the outermost layer of cells in the dicot stem. Its primary function is to protect the internal tissues from water loss, mechanical injury, and invasion by pathogens. The epidermis consists of a single layer of tightly packed cells that secrete a waxy substance called cutin, which forms a protective, waterproof barrier called the cuticle.

Discuss the function of the cortex.

The cortex is located just below the epidermis and acts as a packing tissue, providing support to the stem. It consists of multiple layers of parenchyma cells that store food and water for the plant. Some of these cells may contain chloroplasts and carry out photosynthesis. Additionally, the cortex is involved in transporting water and nutrients across the stem.

Explain the function of the pith.

The pith is the central region of the dicot stem, surrounded by vascular tissues (xylem and phloem). It is composed of large, thin-walled parenchyma cells that store food and water for the plant. The pith also provides structural support to the stem.

Describe the function of the xylem.

The xylem is a vascular tissue found in the dicot stem, with two main functions: conducting water and dissolved minerals from the roots to the upper parts of the plant, and providing structural support to the stem. The xylem consists of dead, elongated cells called tracheids and vessel elements, connected end-to-end to form a continuous column.

Explain the function of the phloem.

The phloem is another vascular tissue present in the dicot stem. Its primary function is transporting food in the form of sugars (products of photosynthesis) from the leaves to the other parts of the plant. The phloem is composed of living cells called sieve tube elements, along with companion cells that support the sieve tube elements.

Describe the changes in the internal structure after secondary growth.

During secondary growth in a dicot stem, the plant undergoes radial expansion, thickening its stem. This process is facilitated by the formation of secondary xylem and phloem. A layer called the vascular cambium, present between the primary xylem and phloem, starts to divide, producing the secondary xylem (wood) toward the inside and secondary phloem (inner bark) toward the outside. As a result, the stem becomes thicker and stronger, with the cortex and epidermis usually being replaced by a protective tissue called the periderm.

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Diagram the internal structure of a dicot stem after primary growth, labeling and describing the function of the epidermis, cortex, pith, xylem, and phloem. How does the structure change after secondary growth?

Short Answer

Step by step solution

Diagram the internal structure of a dicot stem after primary growth.

Describe the function of the epidermis.

Discuss the function of the cortex.

Explain the function of the pith.

Describe the function of the xylem.

Explain the function of the phloem.

Describe the changes in the internal structure after secondary growth.

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