Problem 107 - Objective Biology for NEET

Question

Protonema is found in (a) Liverworts (b) Selaginella (c) Funaria (d) None

Step-by-Step Solution

Answer

The correct answer is (c) Funaria.

Step 1: Understanding the terms

Firstly, understand what protonema is. Protonema is the first stage of the life cycle of mosses and liverworts, when the growth emerges from the spore. Secondly, Liverworts, Selaginella, and Funaria are different types of plants. Liverworts are nonvascular plants belonging to the Marchantiophyta division. Selaginella is a vascular plant and belongs to the division Lycopodiophyta. Funaria belongs to mosses and hence, to Bryophyta division.

Step 2: Interpreting the options

Now based on the understanding of these terms, analyze the options. Liverworts do have a similar stage in their life cycle, but it's not referred to as protonema. Selaginella, being a lycopod, has an altogether different life cycle and does not consist of a protonema phase. Funaria is a moss and therefore, it has a protonema phase, as mosses form protonemal growth after the germination of spores.

Step 3: Select the correct answer

Based on the above reasoning, the only option that fits the description of having a protonema phase is Funaria. Hence, the correct answer is 'Funaria'.

Key Concepts

Moss Life Cycle

The life cycle of mosses is a fascinating journey that begins with a tiny, filamentous growth called protonema. After a moss spore germinates, it gives rise to the protonema, which resembles a tangle of green threads. This stage is crucial as it eventually develops into more complex structures called gametophores—these bear the reproductive organs of the moss.

Mosses exhibit a life cycle known as alternation of generations, which includes two distinct stages: the gametophyte and the sporophyte. The gametophyte is the predominant stage in mosses and is the green, leafy part that we commonly see. This phase produces gametes in specialized structures. When male and female gametes fuse, they form a zygote that grows into the sporophyte—the non-green, stalk-like structure emerging from the gametophyte. This sporophyte produces spores in a capsule at its tip, completing the cycle. These spores then disperse to start new protonemata, continuing the moss life cycle.

Understanding this cycle provides insight into questions such as the one about protonema found in different types of plants.

Liverworts

Liverwort Life Cycle Similarities and Differences

Liverworts, like mosses, are part of the bryophyte group and have a similar life cycle pattern, featuring alternation of generations. However, unlike mosses, the early growth from a liverwort spore is not typically called protonema but may be referred to as a thallus or a gametophyte. Liverworts spread both sexually, through spores, and asexually, through fragments called gemmae.

Their gametophyte stage is often more dominant than the sporophyte, and it can exist in two forms: thalloid liverworts, which are flat and ribbon-like, and leafy liverworts, which resemble small-scale mosses. The liverwort sporophyte is typically less prominent and remains attached to the gametophyte, relying on it for nutrients. This distinction helps in identifying the kinds of growths on various nonvascular plants, furthering comprehension of similarities and differences within bryophytes.

Bryophytes

Defining Bryophytes

Bryophytes are a group of plant species that include mosses, liverworts, and hornworts. They are known for their nonvascular nature, meaning they do not have vascular tissues like xylem and phloem found in other plant groups. This limits their size but also enables them to inhabit a vast range of habitats, especially moist environments where they can absorb water and nutrients directly through their cell walls.

Bryophytes play critical roles in ecosystems, such as soil formation, water retention, and providing habitats for microfauna. They also possess a simple yet intriguing life cycle that demonstrates the early evolutionary stages of plant life cycles. Bryophytes often serve as indicators of environmental quality due to their sensitivity to pollution and changes in their surroundings.

By understanding the group dynamics of bryophytes, students can better grasp the concept of protonema and differentiate between various plant divisions and their unique life cycle stages.