Problem 3 - Biology Today and Tomorrow with Physiology

Question

Epidermis and periderm are ________ tissues. a. ground b. vascular c. dermal d. mesoderm

Step-by-Step Solution

Answer

Epidermis and periderm are dermal tissues.

Step 1: Identify the Question

We need to determine the category of tissues that epidermis and periderm belong to.

Step 2: Understand Tissue Categories

Plant tissues are generally classified into three main types: dermal, vascular, and ground tissues. Dermal tissues cover and protect the plant, ground tissues are involved in photosynthesis, storage, and support, while vascular tissues are responsible for water and nutrient transport.

Step 3: Define Dermal Tissues

Dermal tissue is the outer protective layer of the plant, which includes the epidermis and, in woody plants, the periderm, which replaces the epidermis.

Step 4: Match Epidermis and Periderm to Tissue Type

Since both the epidermis and periderm function as protective layers on the outer surface of the plant, they are categorized as dermal tissues.

Key Concepts

Epidermis

The epidermis is the outermost layer of cells in the plant, functioning as a protective barrier between the plant and its external environment. It plays a crucial role in protecting plants from water loss, pathogens, and physical damage.
It also facilitates the exchange of gases necessary for photosynthesis, thanks to structures known as stomata. These are small openings regulated by guard cells, and they allow carbon dioxide in while releasing oxygen.

• Protection from dehydration: The epidermis helps retain essential water within plant tissues.
• Defense against pathogens: It acts as the first line of defense against pests and diseases.
• Gas exchange and water regulation: Stomata help balance gas exchange and water conservation.

The epidermis can often have a waxy coating called the cuticle for additional protection, particularly in dry environments. This layer not only reduces water loss but also provides an additional shield against external threats.

Periderm

In woody plants, the periderm replaces the epidermis as the protective outer layer as the plant ages. This thicker, more robust layer is vital for continued protection as plants grow in diameter.
The periderm is composed mainly of three layers: the cork, the cork cambium, and the phelloderm. The cork layer, often called bark, is what gives trees their tough protective outer covering.

• Cork: This is the outermost layer that prevents water loss and provides mechanical protection.
• Cork Cambium: A layer of dividing cells responsible for producing the cork cells.
• Phelloderm: A layer of cells produced by the cork cambium located inside the cork itself.

The periderm not only performs protective functions but also has an aesthetic impact, giving trees their characteristic bark appearance. It is crucial for plants that need to reinforce their structure as they mature and expand.

Plant Tissue Types

Plants have a unique system that offers specialized tissues, each with its roles that are key to plant survival and function. The three main types of plant tissues are dermal, ground, and vascular tissues.
Dermal Tissue: As already discussed, this includes both the epidermis and periderm, serving as the outermost layer that protects the plant from external factors.
Ground Tissue: This type handles various critical functions within the plant:

• Photosynthesis: Assists in the conversion of sunlight into energy.
• Storage: Helps store nutrients and water for future use.
• Support: Provides structural integrity to plants, allowing them to hold upright and withstand environmental forces.

Vascular Tissue: Integral for transport in plants, it includes:

• Xylem: Carries water and minerals from roots to the rest of the plant.
• Phloem: Transports sugars and nutrients produced through photosynthesis to different parts.

Understanding these tissue types is essential for recognizing how plants grow, survive, and reproduce. They work together harmoniously to ensure that plants meet their fundamental needs for survival.