Question

The presence of cilia, an oral groove and food vacuoles and the absence of chloroplast in an unicellular organism indicate that the organism carries on
A. Sexual reproduction
B. Autotrophic nutrition
C. Extracellular digestion
D. Heterotrophic nutrition

Answer 1

Hint: Cilia are the small hair-like extensions that are present on the surface of some cells. Food vacuoles are the membrane-bound sac-like structure formed by phagocytosis of food particles. They are present mostly in protozoans.

Complete step by step answer: Sexual reproduction refers to the process that includes the formation and fusion of male and female gametes to give rise to the new organism. It includes two parents and the progeny obtained inherits the genetic traits from both the parents.
Digestion is the process of breaking down the nutrients present in the food into the simpler substances which then are absorbed by cells. Extracellular digestion occurs outside the cells and the organisms exhibiting it secretion the digestive enzyme directly onto the food. The end products of the digestion are absorbed by the cells. However, the presence of food vacuole indicates intracellular digestion wherein food is digested inside the cells. The ingested food is surrounded by a membrane to form the food vacuole. The food vacuole mostly fuses with a lysosome that has the digestive enzymes to digest the food. The digestion products are diffused into the cytoplasm to be used by the cells.
Cilia serve in locomotion or to move the substances across the cell surface. Cilia present on the surface of a unicellular organism are mostly involved in the locomotion.
Autotrophic nutrition is the ability of the organism to synthesize organic substances using simpler inorganic materials. The absence of chloroplasts in the mentioned organism represents its heterotrophic mode of nutrition. This is because chloroplasts are the double membrane-bound organelles that have the pigments called chlorophyll in them. Chlorophyll is the green pigments that trap the sunlight which in turn drives the process of photosynthesis. During photosynthesis, autotrophic organisms synthesize organic substances such as glucose from the raw materials (carbon dioxide and water). The oral groove represents the mouth of heterotrophic, unicellular organisms. It serves as the site for the ingestion of food particles in these organisms.
So, the correct answer is option D. Heterotrophic nutrition.

Note: Paramecium is a unicellular and heterotrophic organism. It is a ciliated organism and has cilia on its cell surface to serve in locomotion. Cilia also serve to drive the food particles into the oral groove. A vacuole is formed around the ingested food wherein the food is digested.