Plastids that are surrounded by more than two membranes are evidence of a. evolution from mitochondria. b. fusion of plastids. c. origin of the plastids from archaea. d. secondary endosymbiosis.

Verified step by step guidance

1. Identify the key term in the question: 'Plastids that are surrounded by more than two membranes'. This indicates a complexity in the structure of plastids.
2. Recall the concept of endosymbiosis in biology, which is a symbiotic relationship where one organism lives inside the other. Primary endosymbiosis involves the engulfment of a bacterium by a eukaryotic cell, leading to organelles like mitochondria and chloroplasts.
3. Understand that secondary endosymbiosis occurs when an already complex eukaryotic cell (that has undergone primary endosymbiosis) is engulfed by another eukaryotic cell. This results in the organelle being surrounded by more than two membranes.
4. Analyze the options given: (a) evolution from mitochondria, (b) fusion of plastids, (c) origin of the plastids from archaea, (d) secondary endosymbiosis. Only option (d) directly relates to the concept of an organelle being surrounded by more than two membranes due to the engulfment by another eukaryotic cell.
5. Conclude that the correct answer is (d) secondary endosymbiosis, as it explains why plastids would be surrounded by more than two membranes.

Key Concepts

Plastids

Plastids are organelles found in the cells of plants and algae, responsible for various functions such as photosynthesis, storage, and the synthesis of other important molecules. They include chloroplasts, chromoplasts, and leucoplasts. The structure of plastids typically involves a double membrane, but some plastids can have additional membranes due to evolutionary processes.

Endosymbiotic Theory

The endosymbiotic theory posits that certain organelles, like mitochondria and plastids, originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells. This theory explains the double membrane structure of these organelles, as they retain their own genetic material and machinery, resembling bacteria. Secondary endosymbiosis refers to a further engulfment event, leading to plastids with more than two membranes.

Secondary Endosymbiosis

Secondary endosymbiosis occurs when a eukaryotic cell engulfs another eukaryotic cell that already contains plastids. This process can result in plastids that are surrounded by multiple membranes, reflecting the original membranes of both the engulfed and the engulfing cells. This concept is crucial for understanding the diversity of plastids in various eukaryotic lineages, particularly in certain algae.