Question

Fusion between two similar gametes, two dissimilar gametes, and non-motile and motile gametes occurs in these organisms respectively.

• A. Chlamydomonas, Volvox, Fucus
• B. Volvox, Spirogyra, Fucus
• C. Chlamydomonas, Spirogyra, Volvox
• D. Spirogyra, Chlamydomonas, Volvox

Hint:

Understanding the types of gamete fusion (isogamy, anisogamy, oogamy) is key to classifying algal reproduction. Chlamydomonas often shows isogamy, Spirogyra exhibits conjugation with functional differentiation, and Volvox displays clear oogamy.

Answer 1

The Correct Option is C

To solve this question, we need to identify the reproductive strategies of the given organisms, focusing on the types of gamete fusion: (i) fusion between two similar gametes (isogamy), (ii) fusion between two dissimilar gametes (anisogamy or oogamy), and (iii) fusion between non-motile and motile gametes. Let’s break this down by analyzing the organisms and their reproductive modes. - Type 1: Fusion between two similar gametes (Isogamy) Isogamy refers to the fusion of two gametes that are morphologically and physiologically similar, meaning they are of the same size and structure. Chlamydomonas, a unicellular green alga, exhibits isogamy in many of its species. In Chlamydomonas, two gametes of the same size and appearance (usually motile with flagella) fuse to form a zygote. While some species of Chlamydomonas can show anisogamy (fusion of dissimilar gametes), isogamy is a well-documented and common reproductive strategy in this genus. Therefore, Chlamydomonas fits the first criterion. - Type 2: Fusion between two dissimilar gametes (Anisogamy or Oogamy) Anisogamy involves the fusion of two gametes that differ in size or structure, such as a smaller motile gamete (sperm-like) and a larger non-motile gamete (egg-like). Oogamy, a specialized form of anisogamy, involves a large non-motile egg and a small motile sperm. Spirogyra, a filamentous green alga, exhibits a form of reproduction called conjugation, which is often considered a primitive form of sexual reproduction. During conjugation in Spirogyra, gametes from two filaments come into contact, and the contents of one cell (acting as the male gamete) move into the other cell (acting as the female gamete) through a conjugation tube. While Spirogyra’s gametes are often described as isogamous in basic terms because they appear similar, the process involves physiological differences (one cell donates its contents, and the other receives), and in some species, there can be slight morphological differences. In the context of this question, Spirogyra is often interpreted as showing a form of dissimilar gamete fusion due to the functional differentiation during conjugation. Thus, Spirogyra fits the second criterion. - Type 3: Fusion between non-motile and motile gametes (Oogamy) This type of fusion is characteristic of oogamy, where a large, non-motile female gamete (egg) fuses with a smaller, motile male gamete (sperm). Volvox, a colonial green alga, exhibits oogamy. In Volvox, sexual reproduction involves the production of a large, non-motile egg within a specialized cell called an oogonium, and smaller, motile sperm produced in an antheridium. The motile sperm swim to the egg to fertilize it, forming a zygote. This clearly matches the description of fusion between non-motile and motile gametes, so Volvox fits the third criterion. Now, let’s evaluate the options: - Option 1: Chlamydomonas, Volvox, Fucus Chlamydomonas matches isogamy (similar gametes). However, Volvox exhibits oogamy (non-motile and motile gametes), not anisogamy (dissimilar gametes). Fucus, a brown alga, also shows oogamy with a non-motile egg and motile sperm, which fits the third criterion but not the second. This option does not match the sequence. - Option 2: Volvox, Spirogyra, Fucus Volvox shows oogamy (non-motile and motile gametes), not isogamy. Spirogyra fits the second criterion (dissimilar gametes in the context of conjugation). Fucus shows oogamy, which fits the third criterion, but the first organism (Volvox) does not match isogamy. This option is incorrect. - Option 3: Chlamydomonas, Spirogyra, Volvox Chlamydomonas matches isogamy (similar gametes). Spirogyra fits the second criterion (dissimilar gametes via conjugation). Volvox matches the third criterion (non-motile and motile gametes via oogamy). This option aligns perfectly with the question’s requirements. - Option 4: Spirogyra, Chlamydomonas, Volvox Spirogyra does not exhibit typical isogamy in the same way Chlamydomonas does; its conjugation involves functional differentiation. Chlamydomonas does not show anisogamy as its primary mode. Volvox fits the third criterion, but the first two do not align correctly. This option is incorrect. Therefore, the correct answer is (3) Chlamydomonas, Spirogyra, Volvox, as it matches the sequence of reproductive strategies: isogamy in Chlamydomonas, anisogamy-like conjugation in Spirogyra, and oogamy in Volvox. Thus, the correct answer is Chlamydomonas, Spirogyra, Volvox.

Answer 2

In sexual reproduction, the fusion of gametes can occur in different ways depending on the organism:

1. Fusion between two similar gametes (Isogamy): In this type of fusion, the gametes are morphologically similar in size and shape. This occurs in the green alga Chlamydomonas, where both gametes are flagellated, similar in size, and capable of movement. This is called isogamy.

2. Fusion between two dissimilar gametes (Anisogamy): Here, the gametes differ in size or form but both are motile. This is seen in Spirogyra, a filamentous green alga, where the gametes that fuse are unequal in size or morphology but both are capable of movement.

3. Fusion between non-motile and motile gametes (Oogamy): In this type, the female gamete is large and non-motile, while the male gamete is small and motile. This kind of fusion occurs in Volvox, a colonial green alga, where the egg (female gamete) is non-motile and the sperm (male gamete) is motile.

This classification highlights the diversity of sexual reproduction in algae and the evolution of gamete types from similar to highly specialized forms.