Problem 10 - Biology: Concepts and Applications

Question

Bark is mainly __________. a. periderm and cork b. cork and wood c. periderm and phloem d. cork cambium and phloem

Step-by-Step Solution

Answer

The correct answer is (c) periderm and phloem.

Step 1: Understand the Anatomy of Bark

Bark is a term that refers to all the tissues outside the vascular cambium in woody plants. It includes several layers of tissues.

Step 2: Identify Components of Bark

Bark primarily consists of the periderm and the secondary phloem. The periderm includes the cork (phellem), cork cambium (phellogen), and phelloderm. The secondary phloem carries nutrients.

Step 3: Evaluate Answer Choices

Evaluate the answer options: (a) includes periderm and cork; (b) includes cork and wood; (c) includes periderm and phloem; (d) includes cork cambium and phloem. Bark is mainly composed of the periderm and phloem.

Step 4: Select the Correct Answer

Among the options, (c) 'periderm and phloem' correctly describes the primary components of bark. The periderm encompasses the protective outer layers, while phloem is responsible for nutrient transport.

Key Concepts

Bark Structure

Bark serves as an essential protective barrier for trees, shielding them from environmental stressors and pests. It is situated outside the vascular cambium and encompasses various layers that contribute to the tree's survival.
The main components of bark include:

• Periderm: This is the outermost layer and acts as a protective skin for the tree. It comprises cork (or phellem), cork cambium (phellogen), and phelloderm. The periderm functions to reduce water loss and protect against physical damage.
• Secondary Phloem: Located just beneath the periderm, this layer transports nutrients produced during photosynthesis to different parts of the plant.

Together, these layers form a complex structure that safeguards the tree, facilitating critical processes such as nutrient transportation and gas exchange while providing structural support.

Periderm

The periderm is a vital adaptation in woody plants that replaces the epidermis, serving as the new protective outer layer. It is a dynamic tissue that aids in protection and water conservation.
The periderm consists of three main components:

• Cork (Phellem): Formed by the phellogen, cork is composed of dead cells that are filled with suberin, a waxy substance that renders them waterproof. This helps reduce water loss and protects the inner tissues from pathogens.
• Cork Cambium (Phellogen): This is a lateral meristem that generates new cork cells on the outside and occasionally phelloderm cells on the inside, maintaining a continuous supply of protective tissue.
• Phelloderm: Located just beneath the phellogen, phelloderm is formed inwardly by the cork cambium and consists of living cells. Although less prominent than cork, it provides additional protection and sometimes contributes to nutrient storage.

With these components, the periderm acts as a barrier against environmental challenges, playing a crucial role in the plant's defense mechanism.

Phloem

Phloem is one of the two types of vascular tissue in plants, the other being xylem. It is primarily responsible for the distribution of nutrients, mainly the sugars produced by photosynthesis, throughout the plant.
Key characteristics of phloem include:

• Sieve Elements: These long tubular cells are involved in transport and have perforated ends that connect with adjacent cells, forming open passages for nutrient movement.
• Companion Cells: Associated with sieve elements, these cells facilitate loading and unloading of sugar into the sieve tubes. They play a crucial role in maintaining the metabolic functions necessary for nutrient transport.
• Phloem Parenchyma: These are storage cells that hold nutrients and other substances, supporting the functioning of the phloem tissue.
• Phloem Fibres: Providing structural support, these fibers help maintain the integrity of the phloem tissue.

Phloem's main function is to provide energy to the plant by distributing sugars and other nutrient substances. It is an integral part of the plant's vascular system, working in tandem with xylem to ensure healthy growth and development.