Which group is incorrectly paired with its description?
a. Diatoms—important producers in aquatic communities
b. Red algae—eukaryotes that acquired plastids by secondary endosymbiosis
c. Apicomplexans—unicellular parasites with intricate life cycles
d. Diplomonads—unicellular eukaryotes with modified mitochondria

Verified step by step guidance

1. Step 1: Begin by understanding the characteristics of each group mentioned in the options. Diatoms are a type of algae known for their silica cell walls and are indeed important producers in aquatic ecosystems.
2. Step 2: Examine red algae. They are eukaryotic organisms that contain plastids, but these plastids were acquired through primary endosymbiosis, not secondary endosymbiosis. This is a key point to consider.
3. Step 3: Consider apicomplexans. These are unicellular parasites, such as Plasmodium, which have complex life cycles often involving multiple hosts. This description is accurate.
4. Step 4: Look at diplomonads. These are unicellular eukaryotes, such as Giardia, that have modified mitochondria known as mitosomes. This description is correct.
5. Step 5: Compare each description with the known characteristics of the groups. Identify the group whose description does not match its known biological features, focusing on the distinction between primary and secondary endosymbiosis in red algae.

Key Concepts

Diatoms

Diatoms are a major group of algae and are among the most common types of phytoplankton. They are important producers in aquatic communities, contributing significantly to the global carbon cycle through photosynthesis. Diatoms have silica cell walls, which give them a unique and intricate appearance under a microscope.

Secondary Endosymbiosis

Secondary endosymbiosis refers to the process by which a eukaryotic cell engulfs another eukaryotic cell that has already undergone primary endosymbiosis. This process is believed to have led to the acquisition of plastids in certain algae, such as red algae, allowing them to perform photosynthesis. It is a key concept in understanding the evolution of complex cells.

Diplomonads

Diplomonads are a group of unicellular eukaryotes characterized by having modified mitochondria known as mitosomes, which lack the ability to perform oxidative phosphorylation. They are often parasitic, with Giardia lamblia being a well-known example that causes gastrointestinal infections in humans. Understanding their unique cellular structure is crucial for studying their biology and pathogenicity.