ParameciumBy: Anastasia Alekseyeva (AA)

(4 Shwetha)

Classification/Diagnostic characteristics

Paramecia are in the kingdom Protista. Protista is a kingdom where organisms other than animals, plants, or fungi are classified.
Paramecium is in the phylum alveolata, which is characterized for having multiple sacs underneath the cell membrane called alveoli.
Paramecium is a genus in the class of ciliates. Ciliates are classified for their numerous hair-like cilia of uniform length that have various functions, the most prevalent of which is movement. Ciliates are also characterized by the procession of two different types of nuclei. Ciliates are also more complex in body form than most unicellular eukaryotes.
Paramecia are shoe shaped, unicellular, and are covered with cilia.

While most eukaryotes only have one DNA-containing nucleus, ciliates such as paramecia have two - one large macronucleus and at least one much smaller micronucleus, which sit next to each other within the cell. The macronucleus controls day-to-day functions associated with growth and reproduction, while the micronucleus remains inactive until the cell undergoes some type of sexual process. This unique characteristic makes it easier to identify ciliates and alters inheritance patterns. (5) (JLev)

Relationship to humans

Paramecia are often used in research; they are the most studied of all of the ciliates. They are used for many forms of biological research, from membrane function to population dynamics.
Paramecium are also used to control algae, bacteria, and other protists. They are helpful with cleaning small debris in water and small animals eat paramecium as food. Some paramecium can cause illness if living inside the human body. (LC) 4

Habitat and niche

Paramecia are widespread in freshwater environments. They are also especially common in scums. Because they feed on bacteria (which often slightly acidify their surroundings), Paramecia are attracted by acidic conditions. Paramecia are an essential link in the detrital food web in aquatic ecosytems as they occupy the niche in which they feed on bacteria and dead organic matter and are consumed by protists and small animals. (6) (JF)

[1] (FZ)
Video of Paramecium Bursaria. Paramecium Bursaria have a symbiotic relationship with green algae (the algae actually live inside the paramecium).

Predator avoidance

Paramecia are covered by an elaborate pellicle, a structure with an outer membrane and an inner layer of closely packed, membrane enclosed sacs called alveoli. The alveoli surround the bases of the cilia. Within the alveoli there are defense organelles called trichocysts. When there is a threat detected, a microscopic explosion will release the trichocysts from the alveoli. The trichocysts emerge as tiny, dart-like points at the end of an expanding filament.

Paramecia are eaten by other protists, as well as many other animals that eat microscopic organisms, such as water fleas and mussels. (4)(KG)

Nutrient acquisition

Paramecia are heterotrophs. They engulf solid food via endocytosis, a process in which a cell completely surrounds a particle with its cell membrane, forming a membrane enclosed pocket within the cell. In paramecia this pocket, when filled with food, is called a digestive vacuole, in which food is digested. Small vesicles containing digested food then pinch away from the digestive vacuole and enter the cytoplasm. These small vesicles allow for more surface area through which the cell can absorb the products of digestion.

In order to gather its food the paramecium uses its cilia to sweep the food along with some water into the cell mouth after it falls into the oral groove. The food goes through the cell mouth into the gullet, which is like the stomach. When there is enough food in it so that it has reached a certain size it breaks away and forms a digestive vacuole.[2] (CC)

Paramecium feed on microorganisms like bacteria, algae, and yeasts. (2)(KG)

(7) (E.S.S.)
Cilia not only aids paramecia in movement and transportation, the hair-like structures that stick out of the cell membrane also help in feeding. They sweep the food (algae, bacteria, etc.) into the oral groove (the dip in the paramecium that leads to their mouths) and into their mouths and through the gullet (the throat of the paramecium). [2] (AY)
Once the food enters into the hair-like structures called the cilia , it is pushed down a pathway where the food travels from the mouth to the stomach called the gullet. The food is broken down by enzymes and hydrochloric acid. After the food is broken down, whatever is left leaves through the thin skin of the paramecium called pellicles.(10)(NC)

Video of paramecium eating pigmented yeast. (8)(BB-V)

Reproduction and life cycle

Paramecia reproduce asexually by binary fission, a process in which nuclei and organelles are copied before the cell divides into two daughter cells. They also partake in a complicated sexual behavior called conjugation.
Paramecia have two types of nuclei within the cell: macronuclei and micronuclei. The cell usually has one macronuclei and one or more micronuclei. The micronuclei are typical eukaryotic nuclei and they are essential in conjugation. The macronuclei contain many copies of genetic information, which is divided into units with a few genes in each one. The macronuclear DNA is transcribed, translated, and used for cell function.
During conjugation, two paramecia line up next to each other and fuse near a region of the body called an oral groove. Nuclear material is exchanged over several hours, and the cells both end up with two haploid micronuclei (nuclei that contain one set of chromosomes), one from the original cell and one from the other cell. The two haploid micronuclei fuse to form one diploid micronuclei (that contains two sets of chromosomes). A new macronucleus develops through a series of complicates chromosomal rearrangements. The cells then separate, each with a new combination of alleles.The paramecium does not have a life span. The paramecium dies when the food supply runs out, when the stream dries up. (HSC)

Life Cycle of a Paramecium - (11) (WSS)

Growth and development

After reproducing via binary fission, the two paramecia quickly return to their full-grown size.


Paramecia are unicellular organisms with a semipermeable cell membrane. Their membrane is an elaborate system called a pellicle, which includes two parts. The outside is a phospholipid cell membrane, and the inside is a layer of closely packed alveoli. Coming out of the membrane are uniform length cilia that entirely cover the cell.


Paramecia use cilia to propel themselves backwards of forwards in a spiraling manner. It does this by coordinating the beating of its cilia. The coordination is the result of a differential distribution of ion channels in the plasma membrane near the two ends of the cell. Cilia are a more accurate and precise form of propulsion than flagella or pseudopods. If a paramecium encounters a barrier or a negative stimulus, it can quickly back off.

Sensing the environment

Paramecia have the ability to sense the environment. They can, for example, back away quickly from a barrier in their path.
Paramecia are organisms that are able to respond to chemical cues in their environment. One chemical which it responds to is the neurotransmitter glutamate. Paramecia are attracted to glutamate although the reason is not completely solidified yet. What is known is that there are receptors on the cells surface that are attracted to glutamate. Also it is known that once in contact with glutamate it causes the paramecium to become hyperpolarized (Being more negative than positive). One way it is thought that the paramecia becomes hyperpolarized is that the glutamate triggers the activation of calcium pumps in the cell membrane which would pump calcium cations out of the cell causing the cell to become more negative. This area is still under intense research. (9) (BH)

Gas exchange

Because paramecia are unicellular, gas exchange occurs through diffusion through the cell membrane. A more complicated system is not required for unicellular organisms.

Oxygen from the surrounding environment of water diffuses through the cell membrane into the cytoplasm, while carbon dioxide diffuses out of the cytoplasm through the cell membrane.[3] (TM)

Waste removal

Paramecia have anal pores for waste excretion.
When the nutritious contents of the vacuoles exit by diffusion, these vacuoles become smaller and the waste products are concentrated. The vacuole moves through the cytoplasm until all the nutrients are extracted, and then the vacuole contacts the anal pore where it lyses and the contents are put into the surrounding environment. This is exocytosis. (3) (MC)

external image paramecvacs.gif (JLau)

Environmental physiology (temperature, water and salt regulation)

Because paramecia like in freshwater, they are hypertonic to their environment and constantly take in excess water through osmosis. To expel the excess water paramecia have a contractile vacuole that excretes the water. After water collects in the vacuole, it contracts and the excess is expelled out of the cell.

Internal circulation

Because the paramecium is unicellular, it does not have an internal circulatory system.

Chemical control (i.e. endocrine system)

Paramecium is a unicellular organism, and as of right now, there are no signs of an endocrine system or its necessity. (ES)

Review Question
1) Hypothesize on the evolutionary mechanisms behind the paramecium's ability to reproduce both sexually and asexually. Why is it advantageous for paramecia to reproduce sexually? How about asexually? (SJ)

2) Paramecium, lacking eyes and complex organ systems, are under intense research. A scientist observed that if a paramecium encounters a barricade, it will back away. Paramecium do not have complex nervous systems. Explain how it might do so. Include an explanation of it moves as well. (AWC)

3) Cilia are an important part of paramecium because they assist in both eating and movement. Explain how cilia function and how they help in these processes. (SM)

4) How do paramecia respond to glutamate? (PS)

5) Paramecium live in freshwater and are constantly expelling water, what would happen if you placed a paramecium in saltwater? (BS)

6) Explain how paramecia acquire food, water, and nutrients. (DM)

7. Explain the differences between the nuclei within the paramecium. (DA)


Everything without a numbered citation is from:
Hillis, David M. Principles of Life. Sunderland, MA: Sinauer Associates, 2012. Print
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