In the life cycle of algae, sexual reproduction that occurs through the fusion of two morphologically similar and equal sized gametes is called ________.

Introduction / Context:
This botany question focuses on the different types of sexual reproduction observed in algae. Algae exhibit a variety of sexual processes depending on the nature and size of the gametes involved. Recognising the correct term for fusion of two similar sized gametes is essential for understanding algal diversity and reproductive strategies, commonly tested in biology exams.

Given Data / Assumptions:
- The context is sexual reproduction in algae. - The question specifies that the two gametes involved are of similar size and morphology. - Various reproductive terms are provided as options. - Standard definitions of isogamy, anisogamy, and oogamy are assumed.

Concept / Approach:
Sexual reproduction in algae is classified based on the structure and relative size of the gametes. In isogamy, the two gametes are morphologically similar and equal or nearly equal in size, often both motile. In anisogamy, the gametes differ in size or form, usually with one being larger than the other. In oogamy, a large non motile female gamete (egg) fuses with a small motile male gamete (sperm). Zoospores, by contrast, are asexual reproductive units that are motile but do not arise from gamete fusion. Therefore, fusion of two similar sized gametes is called isogamous reproduction.

Step-by-Step Solution:
Step 1: Focus on the key phrase in the question: two similar size gametes. Step 2: Recall that in isogamy, gametes are morphologically similar and generally equal in size. Step 3: Remember that anisogamy involves gametes that are dissimilar, with one larger or differently shaped than the other. Step 4: Note that in oogamy, the gametes are highly dissimilar, with a large non motile egg and a small motile sperm, typical of many higher plants and animals. Step 5: Recognise that zoospores are asexual spore like structures and do not describe any type of sexual gamete fusion. Step 6: Conclude that the term describing fusion of similar size gametes is isogamous.

Verification / Alternative check:
Standard botany texts often present a comparative table of isogamy, anisogamy, and oogamy with diagrams. In these, isogamous reproduction is illustrated with two nearly identical motile gametes fusing, whereas anisogamy and oogamy show obvious size differences. Examples of isogamy are given in some species of green algae like Ulothrix and Spirogyra. This consistent description ensures that when you see similar size gametes, isogamous should be the term that comes to mind.

Why Other Options Are Wrong:
Zoospore formation: Zoospores are asexual reproductive bodies produced without gamete fusion, so this term does not describe any sexual process. Anisogamous: This describes sexual reproduction where gametes differ in size or shape, so it cannot apply to the case of similar sized gametes. Oogamous: This form involves a large immobile egg and a small motile sperm, clearly not equal sized gametes.

Common Pitfalls:
Students sometimes confuse isogamy and anisogamy because the words look similar. The prefix iso means equal, which should remind you that isogamous involves equal sized gametes, while aniso indicates unequal. Another pitfall is treating zoospores as any motile cell, failing to distinguish between asexual spores and true gametes. Keeping the key idea of equal versus unequal sizes in mind helps pick the right term quickly.

Final Answer:
Sexual reproduction involving fusion of two similar sized gametes in algae is called Isogamous reproduction.