What Kind of Organism Is the Paramecium? Understanding Its Structure and Function in One Article

Anyone who has studied biology is surely familiar with the paramecium. Although it consists of only a single cell, its growth capacity is also very strong. Let us take a look below at what kind of organism the paramecium is and what its structure and function are.

I. What kind of organism is the paramecium?

The paramecium is a very small, cylindrical protozoan. It is made up of only one cell, making it a single-celled animal. The most common is the Paramecium caudatum. Its body length is only 80 to 300 micrometers. Because its body shape, viewed from a flat angle, resembles the sole of an upside-down straw sandal, it is called the paramecium.

The paramecium belongs to the single-celled animals because it is made up of one cell, has no chloroplasts in its body, and cannot synthesize organic matter on its own. Food enters its body, forms a food vacuole, and is digested within it. Oxygen can be obtained directly from water through the pellicle, and excess water in the body is expelled from the body through the anal pore.

II. What are the structure and function of the paramecium, and what do images show?

The entire surface of the paramecium body is covered with a thin but elastic pellicle, which is equivalent to an ordinary cell membrane. The surface of the pellicle forms many regularly arranged hexagonal or quadrilateral compartments, and each compartment grows 1 to 2 cilia. Under an electron microscope, the pellicle can be seen to be composed of three layers of membrane. The outermost membrane is continuous on the body surface and above the cilia. Between the inner two membranes, pellicle vesicles form near the base of each cilium. The pellicle keeps the body of the paramecium in a certain shape. The pellicle vesicles can both increase the hardness of the pellicle and not affect local bending of the paramecium body; they may also be a kind of buffer zone protecting the cytoplasm, and can prevent internal substances from passing through the outer cell membrane.

Below the pellicle there are many small and slender trichocysts, buried in the ectoplasm and arranged perpendicular to the body surface. The hardness of the trichocysts is in a semi-liquid state, and under certain conditions they can be pressed out of the body through small pores in the pellicle. When the paramecium is attacked, or affected by a weak acid solution, the liquid inside the trichocysts is ejected, and upon contact with water it becomes a slender and sticky thread that can entangle the enemy.

The paramecium is a common, fast-moving protozoan. It has an oval shape, resembling an inverted straw sandal, hence the name. The front end of the paramecium body is relatively blunt, the rear end is relatively pointed, and the middle and rear parts are relatively wide. The body surface is the pellicle, covered with a layer of short cilia. The paramecium swims in water by the beating of the cilia, usually swimming forward with the rounder end first, so this end is called the front end, though sometimes it can also move backward. From the front end of the body begins a groove that extends diagonally toward the middle of the body, called the oral groove. The side with the oral groove is the oral or ventral side of the paramecium. At the bottom of the oral groove is the cytostome, and the cytostome connects internally to the cytopharynx. The long and strong cilia in the oral groove and the cilia in the cytopharynx form the undulating membrane. When the cilia beat, they can roll small organisms such as bacteria in the water into the body, forming food vacuoles at the end of the cytopharynx. In the cytoplasm around the food vacuole, an acid is secreted to dissolve or digest the food, which is then carried away by the slow circulation of the cytoplasm. The digested food is absorbed by the cytoplasm to form new cytoplasm; what cannot be digested is expelled through the anal pore on the ventral side of the rear end. The paramecium has a certain effect on wastewater purification, because one paramecium can form 60 food vacuoles per hour,

each food vacuole can hold 30 bacteria, so each paramecium can swallow 43,200 bacteria in one day. Although the cytostome and anal pore are fixed structures, they can only be seen when the organism swallows or expels solid matter.

The cytoplasm of the paramecium is also composed of a relatively thin, granular endoplasm and a transparent, viscous ectoplasm. In the endoplasm, near the middle of the body, there is a large oval nucleus; there is also one or more small nuclei, located in the indented part of the large nucleus. In the paramecium body, there is one contractile vacuole at the front and one at the back, contracting alternately in a quite regular manner. The position of the contractile vacuoles is fixed. Each time they contract, water containing soluble waste is expelled from the body through small pores in the pellicle, and at this moment the contractile vacuoles can no longer be seen. From the cytoplasm around the contractile vacuoles, radially arranged collecting canals extend to collect water and waste. When the contractile vacuole contracts, the collecting canals become very obvious because they gradually fill with water and waste; when the collecting canals contract, they send the water and waste to the contractile vacuole. Therefore, the expansion and contraction of the two proceed alternately.

Reproduction in the paramecium occurs by transverse binary fission and conjugation, two kinds. The former is asexual reproduction, and the latter is sexual reproduction. In transverse binary fission, the organism elongates along the transverse axis, the nucleus divides first, and the paramecium is constricted transversely into two, taking about two hours from front to back.