Problem 124 - Objective Biology for NEET

Question

Gametophyte of pteridophyte (a) Parasite on sporophyte (b) Not a free living stage (c) Photosynthetical and free living (d) Is unicellular

Step-by-Step Solution

Answer

The correct answer is C) Photosynthetical and free living.

Step 1: Understanding Pteridophytes

Pteridophytes are essentially from the fern group of plants. They switch between diploid sporophyte and haploid gametophyte in their life cycles.

Step 2: Pteridophyte Gametophyte Characteristics

The gametophyte of pteridophytes is not parasitic on the sporophyte. They are free-living and are photosynthetic in nature, utilizing sunlight for their food making processes.

Step 3: Analysing the Choices

\nA) Parasite on sporophyte: From our analysis in Step 2, we know this is false because the gametophyte is free-living. \nB) Not a free living stage: Again, from Step 2, we learn this is false - the gametophyte is free-living. \nC) Photosynthetical and free living: This matches what we concluded in Step 2, so it seems to be the correct answer. \nD) Is unicellular: This is false. The gametophyte of pteridophytes is not unicellular.

Key Concepts

Plant Life Cycles

To fully grasp the nature of pteridophyte gametophytes, it's essential to understand the broader context in which they exist. Plant life cycles exhibit a pattern called alternation of generations, which involves the succession of two distinct forms: the haploid gametophyte and the diploid sporophyte.

In this cycle, the haploid gametophyte stage produces gametes (male and female sex cells) which can merge to form a diploid zygote. This zygote then develops into a diploid sporophyte, which in turn produces haploid spores through meiosis. These spores then grow into new gametophytes, thereby completing the cycle. It's a remarkable and complex dance of cellular division and differentiation that ensures the continuation of plant species.

Pteridophytes, a group that predominantly includes ferns, exhibit this life cycle prominently. Their gametophytes and sporophytes are completely separate stages, with the gametophyte stage being significantly smaller and less conspicuous than the leafy, often-lush sporophyte that most people would recognize as 'a fern.'

Photosynthesis in Pteridophytes

Understanding the photosynthetic capabilities of pteridophytes provides insight into how these plants sustain themselves and contribute to their ecosystems. Photosynthesis in pteridophytes, as with all photosynthetic plants, involves the conversion of light energy into chemical energy, which is stored in the form of glucose and used to fuel vital life processes.

The gametophytes of pteridophytes are photosynthetically active, which means they have the ability to capture light energy using chlorophyll contained within their cells. This energy is then used to convert carbon dioxide and water into sugars and oxygen, the latter of which is released into the atmosphere, contributing to the air we breathe. For students, it’s fascinating to conceptualize that even these small, often overlooked stages of a plant's life are contributing to broader ecological cycles and processes.

Fern Reproduction

Fern Gametophyte Stage

During the gametophyte stage, reproduction begins when the spores – which are released by the sporophyte – grow into a new, multicellular gametophyte plant. This tiny gametophyte, often heart-shaped, nurtures and protects the developing sex cells.

Fern Fertilization

After the gametes are produced, fertilization occurs in the presence of water, as male gametes need to swim to the female gametes. This limitation is one reason why ferns and their relatives typically thrive in moist environments.

Development of Sporophyte

Once fertilization takes place, a new sporophyte begins to grow, eventually giving rise to the familiar large fern structure. This sporophyte will produce fronds and eventually spores of its own, which allows the life cycle to continue. The fascinating aspect of fern reproduction is the independence of the sporophyte stage; unlike some other plants, once it is established, it is self-sufficient and does not rely on the gametophyte for sustenance.