In algae, sexual reproduction that occurs through the fusion of two gametes of dissimilar size is termed by which specific type?

Introduction / Context:

Algae exhibit a variety of reproductive strategies, including asexual and sexual methods. In sexual reproduction, the fusion of gametes can occur under different patterns depending on their size and motility. Recognising these patterns helps students understand evolutionary trends in reproduction from simple to more complex organisms. This question focuses on the type of sexual reproduction in algae where two gametes that fuse are of different sizes but may both be motile.

Given Data / Assumptions:

• The organisms are algae undergoing sexual reproduction.
• The key condition is that two gametes of dissimilar size fuse.
• Options include anisogamous, isogamous, oogamous, zoospore formation, and asexual fragmentation.
• We assume standard definitions of isogamy, anisogamy, and oogamy as taught in school botany.

Concept / Approach:

In isogamy, gametes that fuse are morphologically similar in size and structure, though they may be physiologically different. In anisogamy, gametes differ in size or form but both are usually motile; one is larger and one is smaller. In oogamy, there is a large non motile female gamete (egg) and a small motile male gamete (sperm). The question states that two dissimilar size gametes fuse, which matches the definition of anisogamy. Zoospore formation and fragmentation are asexual processes and do not involve gamete fusion, so they can be excluded.

Step-by-Step Solution:

Step 1: Identify that the question describes sexual reproduction involving fusion of gametes. Step 2: Recall the definitions: isogamy for similar gametes, anisogamy for dissimilar gametes of motile type, and oogamy for highly dissimilar gametes with a non motile egg. Step 3: Note that the question specifically mentions dissimilar size but does not require an egg type structure, which fits anisogamy. Step 4: Exclude zoospore formation and fragmentation as they are asexual and lack gamete fusion. Step 5: Select anisogamous (anisogamy) as the correct type of sexual reproduction described.

Verification / Alternative check:

Botany textbooks that discuss algae such as Eudorina and Pandorina describe anisogamy where the gametes differ slightly in size. They contrast this with isogamy in green algae like Ulothrix, where gametes are similar, and oogamy in higher algae and plants, where a large egg is fertilised by a small sperm. Diagrams often label anisogamous species and show the size difference. These explanations confirm that the fusion of two dissimilar sized gametes in algae is called anisogamy.

Why Other Options Are Wrong:

Option A, Zoospore formation, refers to asexual reproduction through motile spores and does not involve gametes. Option C, Isogamous, involves gametes that are morphologically similar, which contradicts the condition of dissimilar size. Option D, Oogamous, involves fusion of a large non motile egg with a small motile sperm and is typically considered a more advanced type than simple anisogamy. Option E, Asexual fragmentation, refers to breaking of the plant body into pieces that grow into new individuals, again with no gamete fusion.

Common Pitfalls:

Students may confuse anisogamy with oogamy because both involve gametes that are not identical. If they do not pay attention to whether the female gamete is non motile and egg like, they may choose oogamy incorrectly. Others may simply recall that isogamy and anisogamy are terms used in algae but forget which one means similar and which one means dissimilar. To avoid these errors, learners should link iso with equal and remember that anisogamy is unequal but still often motile, while oogamy is egg based with one non motile gamete.

Final Answer:

The sexual reproduction in algae through fusion of two dissimilar sized gametes is called anisogamous (anisogamy).