Problem 17 - Objective Biology for NEET

Question

Isogamy is seen in (a) Chlamydomonas (b) Spirogyra (c) Both (a) and (b) (d) None of these

Step-by-Step Solution

Answer

(a) Chlamydomonas

Step 1: Analyze Chlamydomonas and Spirogyra

Research or recall knowledge about the reproduction methods of Chlamydomonas and Spirogyra. Chlamydomonas is a type of green algae that can reproduce sexually and asexually. With sexual reproduction, it undergoes isogamy, where the gametes are similar in size and shape. In contrast, Spirogyra is also a type of green algae, but during sexual reproduction, it undergoes conjugation, not isogamy.

Step 2: Compare the results

After analyzing both species, it can be seen that only Chlamydomonas exhibits isogamy, not Spirogyra. Therefore, the statement that both species show isogamy is incorrect.

Step 3: Final Answer

Based on the analysis, it can be seen that the correct answer is (a) Chlamydomonas.

Key Concepts

Chlamydomonas Reproduction

Understanding how Chlamydomonas, a form of green algae, reproduces is fundamental in the study of biology. This unicellular organism is known for its versatile modes of reproduction. Asexually, it divides through mitosis, where one cell splits to become two genetically identical cells. However, sexual reproduction is where Chlamydomonas displays isogamy.

Isogamy involves the fusion of two gametes that are morphologically and functionally similar. This process in Chlamydomonas begins when environmental conditions trigger the need for genetic diversity, such as changes in nutrients or light. The algae produce two gametes, which can be seen swimming with the help of their flagella until they find and fuse with another gamete. This fusion results in a zygote that eventually undergoes meiosis to produce new cells with varied genetic backgrounds, enhancing the species' ability to adapt to changing environments.

Now, let's illustrate this process using a simple analogy. Imagine a dance where all participants are wearing similar outfits, moving around the dance floor until they find a partner who matches their dance style perfectly. Upon finding each other, they pair up to perform a new dance routine together, representing the fusion of gametes in isogamy.

Spirogyra Reproduction

Spirogyra is another type of green algae that has a distinct way of reproducing compared to Chlamydomonas. Known for its filamentous, chain-like structures, Spirogyra primarily undergoes asexual reproduction by fragmentation; however, it also engages in a form of sexual reproduction called conjugation.

During conjugation, two filaments of Spirogyra lay side by side, and a conjugation tube forms between them. The cells of one filament transform into mobile gametes, which travel through the tube and fuse with the stationary cells of the other filament, creating a zygote known as a zygospore. Unlike isogamy, this does not involve the fusion of morphologically similar gametes.

Picture two neighbouring strands of pearls, where one strand sends a pearl across a bridge to another strand. This 'gifted' pearl then merges with a pearl from the receiving strand, a vivid image of how Spirogyra gametes combine. This unique process contributes to the genetic variability of the species, crucial for their survival and adaptability.

Sexual Reproduction in Algae

Sexual reproduction in algae is a diverse and complex process that can provide a competitive edge in survival. Algae exhibit a range of reproductive strategies, including both isogamy and another type called oogamy, where the gametes differ in size and structure.

In isogamous species, like some strains of Chlamydomonas, the gametes are identical, promoting genetic diversity without favoring larger or more mobile gametes, as seen in oogamy. On the other hand, oogamous reproduction, characteristic of many multicellular algae, involves a larger, non-motile female gamete (egg) and a smaller, motile male gamete (sperm).

These varied reproductive strategies illustrate the evolutionary adaptability of algae. By utilizing different methods, they can thrive in a multitude of ecological niches, from freshwater ponds to deep ocean waters. In learning about the sexual reproduction of algae, we unlock insights into their survival mechanisms, evolutionary trends, and the intrinsic beauty of their life cycles, revealing the wondrous adaptability of life itself.