Question

From which algal group did green plants probably arise? Explain the evidence that supports this hypothesis.

Short answer

Green plants probably arose from the green algae (Chlorophyta) group. They share several features such as chlorophyll a and b, the same photosynthetic byproducts, similar cell structures, the storage of starch, and similar reproductive processes. Evidence supporting this hypothesis includes genetic studies, fossil records, and the theory of endosymbiosis. Molecular sequencing, phylogenetic analyses, and the age of fossils suggest that green plants and green algae share a common ancestor, which likely merged with a photosynthetic cyanobacterium through endosymbiosis, giving rise to chloroplasts.

Step-by-step solution

Identify the algal group

The algal group from which green plants probably arose is the green algae (Chlorophyta).

Discuss the similarities between green plants and green algae

Green plants and green algae share several features, such as: 1. Both contain chlorophyll a and b, which are the main pigments responsible for photosynthesis. This allows them to capture and utilize sunlight to produce energy. 2. Both have the same photosynthetic byproducts, such as oxygen and glucose. 3. They share similar cell structures, including cellulose-based cell walls and the presence of chloroplasts, which are essential for photosynthesis. 4. The storage of starch as a primary reserve of carbon and energy. 5. They have similar reproductive processes, including alternation of generations, with both haploid and diploid stages.

Explain scientific evidence supporting the hypothesis

The evidence supporting the hypothesis that green plants arose from green algae includes: 1. Genetic studies: Molecular sequencing and phylogenetic analyses of genes encoding for the large and small subunits of the ribulose-bisphosphate carboxylase protein (rbcL and rbcS) have shown that green plants and green algae are closely related, with green algae being the sister group to plants (Mishler et al., 1994). 2. Fossils: The oldest known green plant fossils are about 1 billion years old, similar to the age of the oldest green algae fossils. This suggests that the two groups share a common ancestor. 3. Endosymbiosis: Both green plants and green algae are believed to have descended from a common ancestor that merged with a photosynthetic cyanobacterium through a process known as endosymbiosis. This event gave rise to the chloroplasts we see in green plants and green algae today.

Conclude the explanation

In conclusion, green plants likely arose from the green algae group based on their shared features, genetic evidence, fossil records, and the theory of endosymbiosis. These similarities and research findings provide strong support for the hypothesis of the evolutionary connection between green plants and green algae.