Question

Which of the following is the term for the outer layer of a lichen? a. the cortex b. the medulla c. the thallus d. the theca

Short answer

a. the cortex

Step-by-step solution

Understand the Question

The question is asking for the term that describes the outer layer of a lichen.

Identify the Options

Review the given options: a. the cortex b. the medulla c. the thallus d. the theca

Define Each Term

Lookup each term: the cortex - The outer layer of certain organisms or structures. the medulla - The inner region of an organ or tissue. the thallus - The body of a lichen. the theca - A sac, sheath, or case enclosing an organ.

Match the Definition to the Context

Since the question is about the outer layer, the term 'the cortex' is most appropriate, as it refers to an outer layer.

Select the Correct Option

The correct term for the outer layer of a lichen is option (a) the cortex.

Key concepts

outer layer of lichen

Lichens have a unique and fascinating structure. The outer layer of a lichen, known as the cortex, is essential to its overall function and protection. This outermost layer serves as a protective covering for the lichen, shielding it from harsh environmental factors like extreme temperatures and UV radiation. The cortex is typically composed of tightly packed fungal cells that provide stability and durability, helping the lichen to survive and thrive in various habitats.
Because lichens often grow on exposed surfaces such as rocks, trees, and soil, the protective role of the cortex becomes even more significant.
Understanding this outer layer is crucial for recognizing how lichens adapt to their environments and fulfill their roles in ecosystems as pioneering organisms.

cortex

The term 'cortex' in the context of lichens refers specifically to the outer protective layer. It is a vital component of lichen anatomy, providing both defense and structure. The cortex consists mainly of densely packed fungal hyphae, which form a strong barrier against external damage.
In some lichens, the cortex also includes pigments that offer protection from ultraviolet light. These pigments can give lichens their distinctive colors, ranging from greens to browns and even bright yellows.

• Protects internal structures
• Provides mechanical strength
• Contains pigments for UV protection

The development and maintenance of the cortex are crucial for the longevity of lichen, enabling it to establish itself in a variety of environments and endure periods of environmental stress.

lichen structure

The structure of a lichen is surprisingly complex, considering it is a symbiotic relationship between fungi and algae or cyanobacteria. This intricate structure is divided into several layers, each with distinct roles:
The upper cortex, composed of fungal cells, is the protective outer layer. Below the cortex is the algal layer, where photosynthesis occurs, providing essential nutrients for the fungus. Beneath the algal layer is the medulla, which mainly consists of loosely packed fungal hyphae, allowing for gas exchange and water storage. Finally, some lichens have a lower cortex that further protects and anchors the lichen to its substrate.
These layers work together seamlessly, ensuring the lichen's functionality and ecological success, highlighting the complexity and efficiency of this mutualistic partnership.

cortex function

The cortex of a lichen has several critical functions that contribute to the organism's survival. As the outermost layer, one of its primary roles is protection.
The cortex shields the delicate inner components of the lichen from physical damage, desiccation from harsh winds, and harmful UV radiation from direct sunlight. It also plays a part in regulating water loss, maintaining a balance that allows the lichen to endure drought conditions.

• Protection from environmental stress
• Regulation of water balance
• Defense against UV radiation

Moreover, in some lichens, the cortex may secrete substances that deter herbivores and inhibit the growth of competing organisms.
Overall, the cortex is not just a passive barrier but an active participant in the survival and resilience of lichen as a whole.