Chapter 19, Problem 3A

Summary Introduction

Introduction : 

Organisms belonging to the Kingdom Protista are eukaryotes. A eukaryotic organism or a eukaryotic cell is characterized by the presence of membrane-bound organelles and the presence of the 80S ribosome.

Answer to Problem 3A

Correct answer : 

The correct answer is option (c) endosymbiosis.

Explanation of Solution

Explanation/justification for the correct answer :

Option (c) endosymbiosis. The process of endosymbiosis is based on the symbiotic relationships among organisms. It has been stated and believed that during earlier times some large prokaryote engulfed small prokaryotes that somehow escaped the degradation and survived in the large prokaryote. These engulfed organisms then turned into the organelles like mitochondria and chloroplast and the larger prokaryote then turned into a eukaryotic cell having membrane-bound organelles. The evidence of this theory is given by the similarity between prokaryotes and organelles like chloroplast and mitochondria. So, the correct answer is option (c).

Explanation for incorrect answer : 

Option (a) aerobic respiration. Aerobic respiration is a process in which the organism uses oxygen during respiration. Such organisms require oxygen to survive but have no role in the formation of protists as some prokaryotes also follow aerobic mode of respiration. So, this is an incorrect option.

Option (b) decomposition. It is a process of breaking down dead and complex organic substances into simpler inorganic or organic matter. Decomposition is also done by prokaryotes and thus has no role in the formation of protists. So, this is an incorrect answer.

Option (d) photosynthesis. Photosynthesis is the process of the formation of complex organic substances or glucose using sunlight, water, and carbon dioxide. Photosynthesis is carried out in chloroplasts in eukaryotes and chloroplast is believed to have evolved through the process of endosymbiosis. So, this is an incorrect answer.