Which arrangements of the organisms represents a rank ordering (based on size/importance) from dominant gametophyte on the left to dominant sporophyte on the right?

Options

A. Polytrichum,Cycas,Equisetum
B. Lycopodium,Zostera,Riccia
C. Sphagnum,Pteridium,Cedrus
D. Pinus,Selaginella,Marchantia

Answer

To determine the correct arrangement of organisms that represents a rank ordering from dominant gametophyte to dominant sporophyte, we need to analyze the life cycles of the organisms mentioned in the question. Here’s a step-by-step breakdown:

### Step 1: Understand the Concept of Alternation of Generations
- **Definition**: Alternation of generations is a reproductive cycle in plants and some algae where the organism alternates between a haploid gametophyte generation and a diploid sporophyte generation.
- **Importance**: In some groups of plants, one generation is more dominant than the other in terms of size and importance.

### Step 2: Identify the Dominant Generation in Sphagnum
- **Organism**: Sphagnum (a type of bryophyte)
- **Dominant Generation**: In Sphagnum, the gametophyte is the dominant generation and is haploid. The sporophyte is dependent on the gametophyte and is diploid.
- **Conclusion**: Sphagnum represents the left end of our ranking (dominant gametophyte).

### Step 3: Identify the Dominant Generation in Pteridium
- **Organism**: Pteridium (a type of pteridophyte)
- **Dominant Generation**: In Pteridium, the gametophyte is also dominant, but it is more complex than in bryophytes. The sporophyte is still dependent on the gametophyte but is more developed than in Sphagnum.
- **Conclusion**: Pteridium represents a middle position in our ranking.

### Step 4: Identify the Dominant Generation in Cedrus
- **Organism**: Cedrus (a type of gymnosperm)
- **Dominant Generation**: In Cedrus, the sporophyte is the dominant generation, which is diploid. The gametophytes are reduced and dependent on the sporophyte.
- **Conclusion**: Cedrus represents the right end of our ranking (dominant sporophyte).

### Step 5: Arrange the Organisms
Based on the analysis:
1. **Sphagnum** (dominant gametophyte)
2. **Pteridium** (intermediate, still has a dominant gametophyte but more developed sporophyte)
3. **Cedrus** (dominant sporophyte)

### Final Answer
The correct arrangement from dominant gametophyte to dominant sporophyte is:
**Sphagnum → Pteridium → Cedrus**

---