Contractile vacuole function, diagram, and structure

The contractile vacuole function in certain organisms as a structure for the regulation of water levels. This organelle is found mostly in single-celled organisms that lack a cell wall. Basically, the function of the contractile vacuole is to expand and contract in order to regulate the water levels in and outside the cell. Contractile vacuoles (CV) are not the same as the other type of vacuoles in animal or plant cells that store food or water.

What is a contractile vacuole?

A contractile vacuole (CV) is a sub-cellular organelle in an organism that is involved in osmoregulation. This structure was previously known as the pulsatile or pulsating vacuole. It is a special kind of vacuole found in certain organisms most especially single-celled organisms that do not have a cell wall. Contractile vacuoles can be found predominantly in the kingdom Protista e.g amoeba and unicellular algae.

As the name suggests, a contractile vacuole expands and contracts to pump water out of the cell through a process known as osmoregulation. Osmoregulation involves the regulation of osmotic pressure. Contractile vacuoles occur in freshwater protists but occur mainly in the kingdom Protista as a whole. However, not all species with a contractile vacuole inhabit freshwater habitats, some are marine and soil microorganisms.

In as much as the contractile vacuoles are predominant in organisms without cell walls, there are few exceptions. The CV through the process of evolution was mostly eliminated in multicellular organisms. Nevertheless, this organelle still exists in the unicellular stage of several multicellular fungi and in several types of cells in sponges, such as pinacocytes, amoebocytes, and choanocytes.

Contractile vacuole definition in biology

Contractile vacuole can be defined in biology as a specialized vacuole in eukaryotic cells such as protozoa that are involved in osmoregulation. This organelle allows the flow of water from the cytoplasm of the cell and then by opening a permanent narrow neck, it discharges the water externally. In order words, a contractile vacuole is a structure that collects extra water and expels it from a protist or other organisms.

Contractile vacuoles are regulatory organelles. These organelles are usually spherical or star-like and can be found in freshwater protozoa and lower metazoans, such as sponges and hydras. The function of the contractile vacuole is to collect excess fluid from the protoplasm and periodically empty it into the surrounding medium. Also, the contractile vacuole function in the excretion of nitrogenous wastes. For example, sponges have a contractile vacuole that squeezes out waste.

How are contractile vacuoles different from other types of vacuoles?

A contractile vacuole is not like other types of vacuoles. Generally, vacuoles are membrane-bound sacs that are seen in various cell types. These organelles are seen in protists, plant cells, fungi, and some animal cells. However, contractile vacuoles should not be confused with the vacuoles that store food or water. Contractile vacuoles differ from other types of vacuoles because they can contract and expand to regulate the amount of water in the cell.

The other types of vacuoles have specific functions in the cells they are found in but a contractile vacuole is seen mostly in protists and unicellular algae. In freshwater habitats, the concentration of solutes in the cell is usually higher than the concentration of solutes outside the cell. Due to such conditions, water flows from the environment into the cell via osmosis. Under such conditions, the contractile vacuole function as a protective mechanism against cellular expansion (or explosion) from too much water. In the cell, the contractile vacuole is used to expel excess water from the cell by contracting.

Moreso, depending on the species, the filling and emptying cycle of water by a CV may last from seconds to a minute. The contractile vacuole in the amoeba changes position in relation to the organism’s movement. In most ciliates, contractile vacuoles follow a definite path through the cell. Whereas, the contractile vacuole in euglena and other flagellates remains stationary.

Water usually flows into the cytoplasm first from outside the cell of the organism and moves only into the CV from the cytoplasm for expulsion. Species with CV always use the organelle even in very hypertonic (high concentration of solutes) environments. This is because the cell tends to adjust its cytoplasm to become even more hyperosmotic than the environment. The rate of contraction of the CV and the amount of water expelled from the cell are related to the osmolarity of the environment. For instance, in a hyperosmotic environment, the amount of water expelled would be less and the contraction cycle will be longer.

Contractile vacuole structure

The structure of a contractile vacuole is not like other types of vacuoles that store food or water. When viewed with an electron microscope, the contractile vacuole structure is seen to be surrounded by a system of membranous vesicles and (or) tubules.

In most cells, several structures such as membrane folds, tubules, water tracts, and small vesicles are attached to the CV. These structures are known as the spongiome. Contractile vacuoles may also be associated with canals and a pore to the exterior. The CV together with the spongiome form the contractile vacuole complex (CVC).

Contractile vacuole diagram

contractile vacuole structure in an euglena
A contractile vacuole structure as shown in the diagram of a euglena

How does the contractile vacuole work?

When there is too much water, the contractile vacuole is used to expel excess water from the cell by contracting. In the cell, a set amount of solute (other material) vs solvent (water) is needed. This means the water in the cell needs to be in balance with other materials in the cell.

The cell works via osmosis and water moves across a semi-permeable membrane. The contractile vacuole, therefore, works to pump water out when the water is too much. This protects the cell because when there is excess water in the cell, the cell swells and swell until it ruptures and dies.

The contractile vacuole work to keep this water balance in check and the growth (water collection), as well as a contraction (water expulsion) of the CV, occur periodically. One cycle can take several seconds. This depends on the species and the osmolarity of the environment. Contractive vacuoles expand when water enters, and the stage at which water flows into the CV is called diastole. When the CV is filled with water, it contracts and takes the water along with the wastes outside of the cell. This stage of the contraction and expulsion of water out of the cell by the CV is called systole.

Diagram showing the Contractile vacuole function
A contractile vacuole expands and contracts to pump water out of the cell

How water enters the CV has not been really clear for years but there are several discoveries since the 1990s that have enhanced the understanding of the process. Theoretically, water could cross the membrane of the CV by osmosis, though only if the inside of the contractile vacuole is hyperosmotic to the cytoplasm. This means only if there is a higher solute concentration inside the CV than in the cytoplasm. Moreso, the pumping of protons either into or out of the contractile vacuoles can cause different ions to enter the CVs. For instance, some proton pumps function as cation exchangers, whereby a proton is pumped out of the CV and at the same time, a cation is pumped into the CV.

In other cases, protons pumped into the contractile vacuole drag anions with them (e.g carbonate) in order to balance the pH. This ion flux into the CV causes an increase in the osmolarity of the CV and due to this, water enters the vacuole by osmosis. In some species, water has been shown to enter the contractile vacuole through aquaporins. Moreso, acidocalcisomes have been implied to work together with the CV in responding to osmotic stress.

Acidocalcisomes are acidic calcium-storage organelles seen in diverse organisms. These organelles were detected in the vicinity of the vacuole found in Trypanosoma cruzi. When the cells were exposed to osmotic stress, acidocalcisomes were seen to fuse with the vacuole. Presumably, these organelles empty their ion contents into the contractile vacuole, thus increasing the osmolarity of the vacuole.

Contractile vacuole functions

  1. The function of the contractile vacuole is to protect the cell from absorbing too much water. CVs prevents the cell from potential explosion or lysis by excreting excess water.
  2. Contractile vacuoles function in a periodic cycle to release water. They do this by expanding while collecting water and contracting to excrete the water.
  3. The contractile vacuole is used to excrete wastes that are soluble in water e.g ammonia. These wastes are excreted from the cell along with the excess water.
  4. Salts are also removed through the contractile vacuole in order to maintain the osmotic balance of the cell.

What is the function of a contractile vacuole?

Contractile vacuoles are present in the cells of lower organisms to play an essential role in excretion and osmoregulation. Wastes such as ammonia and other salts can be excreted through the vacuoles in order to maintain the osmotic balance. Hence, the function of the contractile vacuole complex (CVC) is to act as an osmoregulatory organelle in organisms.

In free-living amoebae and protozoa, the CVC controls the intracellular water balance by collecting and expelling excess water out of the cell. For instance, in pond water, this allows the cells to survive under hypotonic stress. Without a functional CV complex, cells cannot expel water. They, therefore, become highly swollen and lyse

Contractile vacuole in protists

The contractile vacuole is an organelle found in protists such as paramecium, amoeba, euglena, Dictyostelium, and Trypanosoma. These organisms have the best understood contractile vacuoles and the role of the contractile vacuole in these unicellular organisms is to remove excess water from the cell. The number of contractile vacuoles per cell varies according to species. For instance, Amoeba has one CV whereas organisms such as Paramecium aurelia, Dictyostelium discoideum, and Chlamydomonas reinhardtii have two. Then, giant amoeba such as Chaos carolinensis, have many CVs. The number of CVs in each species is mostly constant and is usually used for species characterization in systematics.

Paramecium

Paramecium (paramecia) is a single-celled protist that naturally inhabits aquatic habitats. This organism has a large contractile vacuole with an average diameter of 13 um. There are two types of vacuoles seen in a paramecium- a contractile vacuole and a food vacuole. Nevertheless, the paramecium has two contractile vacuoles that are close to the dorsal side, one CV on each end of the body.

The contractile vacuole of a paramecium is comfortable to isolate, manipulate and assay. Presumably, the paramecium has the most complex and highly evolved contractile vacuole which is surrounded by several canals. Each of the paramecium’s contractile vacuole is connected to at least 5-12 radical canals that consist of a long ampulla. An ampulla is a terminal part and an injector canal that is short and opens directly into the CV.

These canals absorb water from the cytoplasm through osmosis and after they are filled with water they pump the water into the CV. Once the contractile vacuole in paramecium is full, it expels the water via a pore in the cytoplasm that can open and close. Therefore, the function of these canals is to pour all the liquid collected from the body of the paramecium into the CV. This eventually makes the vacuole increase in size and the liquid is then discharged outside by the CV through a permanent pore. The process used to remove excess water from the paramecium by the contractile vacuole is active transport because the paramecium’s contractile vacuoles used for the elimination of water are physical pumps. The contractile vacuole function in paramecium is to pump the water out of the cell to avoid cytolysis, the bursting of the cell membrane.

Normally, the contractile vacuole of a paramecium should be active when the paramecium is in a hypotonic environment. The two vacuoles in the paramecium are usually filled with fluids and located at a fixed position between the endoplasm and ectoplasm of the paramecium. However, the paramecium’s contractile vacuole disappears periodically and is therefore called temporary organs. Furthermore, the contraction of the contractile vacuole in paramecium is irregular. The posterior contractile vacuole of the paramecium is close to the cytopharynx and thus contract more quickly because more water passes through it. Therefore, the function of contractile vacuole in paramecium includes excretion, respiration, and osmoregulation.

Amoeba

Amoeba possesses one large contractile vacuole with an average diameter of 45 µm which is relatively comfortable to isolate, manipulate and assay. The function of contractile vacuole in amoeba is to excrete cellular waste e.g ammonia and excess water by exocytosis. This is done by the CV merging with the cell membrane to expel the waste into the environment. The contractile vacuole in the amoeba moves to the surface of the cell when full and undergoes exocytosis. Generally, the function of contractile vacuole in amoeba is to collect excretory waste from the intracellular fluid through diffusion and active transport.

Euglena

Euglena is a eukaryotic cell with complex cell organelles such as the CV. The contractile vacuole in the euglena is anterior and fixed. Moreso, the function of contractile vacuole in euglena is to expel the excess water in the cell towards the reservoir. Hence, the euglena contractile vacuole function to stop the cell from exploding due to excess water. This means that without the CV in the euglena, the cell will explode or lyse from taking in too much water due to osmosis.

Contractile vacuole vs central vacuole

A central vacuole is a type of vacuole found in plant cells. This vacuole is large occupying the center of the plant cell and is surrounded by cytoplasm. How the central vacuole in plant work is slightly different from the contractile vacuole in protists. This organelle in plants is involved in the storage of water, ions, enzymes, pigments, and waste products. Other functions of the central vacuole include maintaining the turgor pressure in plant cells, facilitating photosynthesis, molecular degradation, and disposal of metabolic waste.

Free-living single-celled organisms such as amoeba and euglena do not have a central vacuole like plants. These organisms live in fresh water and osmosis is a big problem for them. They constantly take up water across the semi-permeable membrane and require a contractile vacuole in order not to burst. These unicellular organisms would collect excess water into a CV that contracts and when the CV is filled up, the vacuole connects with the outside and pumps the water out of the cell in order for the organism to survive.

Video illustration

In the video below, close to the dorsal side of the paramecium, two contractile vacuoles can be seen. One CV on each end of the body. You can observe how these CVs contract to expel water. The paramecium’s contractile vacuole disappears periodically as seen in the video.

A video showing the contractile vacuole in paramecium

FAQs

Where do contractile vacuoles occur?

Contractile vacuoles occur in some organisms most especially single-celled organisms that do not have a cell wall. They can be found predominantly in the kingdom Protista e.g amoeba and unicellular algae.

What does the contractile vacuole do in a paramecium?

The contractile vacuole function in paramecium is to pump water out of the cell to avoid bursting of the cell membrane.

What is the role of the contractile vacuole in a protist?

The role of contractile vacuole in a protist is for osmoregulation and the excretion of waste. In protists, the contractile vacuole is used to collect water from the cytoplasm of the cell, and then by contracting, it expels the water out of the cell. Also, the function of contractile vacuole in protists is to excrete nitrogenous wastes.

How would the contractile vacuole of a freshwater amoeba respond?

The contractile vacuole in a freshwater amoeba is a specialized type of vacuole that regulates the quantity of water inside the amoeba. Usually in freshwater habitats, the concentration of solutes is hypotonic. This means the solute concentration is lesser outside than inside the cell.

Under such conditions, due to osmosis, water accumulates in the cell from the external environment. The contractile vacuole of a freshwater amoeba responds by acting as a protective mechanism that prevents the cell from absorbing too much water. This prevents the freshwater amoeba from rupturing through excessive internal pressure.

How does the contractile vacuole in a single-celled organism function to maintain homeostasis?

The contractile vacuole in single-celled organisms functions in a way that maintains homeostasis. Homeostasis is the ability of an organism to maintain the body’s internal environment within limits that allow it to survive.

For instance, in aquatic single-celled organisms like protozoa and algae, the cell is hypertonic relative to its surrounding. This means inside the cell has a higher concentration of solutes than the environment. Due to this, water flows into the cell through osmosis.

The contractile vacuole maintains homeostasis by preventing excessive water influx that could harm and cause rupture (lysis) to the cell. It contracts to expel water out of the single-celled organism.

What is the purpose of a contractile vacuole?

A contractile vacuole is a special kind of vacuole in eukaryotic cells, such as certain unicellular algae and protozoa. The purpose of a contractile vacuole in organisms is for osmoregulation. Osmoregulation involves the regulation of the water potential in organisms in order to maintain the fluid and electrolyte balance within the organism relative to the surrounding. It is essential because it maintains a constant optimal osmotic pressure in the cell. Through it, the cell is able to keep the right amount of solute concentration and water.

How does the contractile vacuole in a paramecium help maintain homeostasis?

The contractile vacuole in a paramecium help maintain homeostasis. Homeostasis is the ability of an organism to maintain the body’s internal environment within limits that allow it to survive. Hence, the contractile vacuole function in paramecium is to pump the water out of the cell to avoid cytolysis, the bursting of the cell membrane.

How does the contractile vacuole help the paramecium survive in a freshwater environment?

Usually in freshwater habitats, the concentration of solutes is hypotonic. This means the solute concentration is lesser outside than inside the cell. As a result, the contractile vacuole of a paramecium should be active when the paramecium is in a hypotonic environment.

Due to osmosis in a freshwater environment, water accumulates in the paramecium from the external environment. The contractile vacuole helps the paramecium survive in a freshwater environment by pumping the water out to prevent the freshwater paramecium from rupturing through excessive internal pressure.

What does the contractile vacuole do?

Contractile vacuoles are present in the cells of lower organisms to play an essential role in excretion and osmoregulation. Wastes such as ammonia and other salts can be excreted through the vacuoles in order to maintain the osmotic balance. Hence, the function of the contractile vacuole complex (CVC) is to act as an osmoregulatory organelle in organisms.

Is contractile vacuole active or passive?

The process used to remove excess water from the organisms by the contractile vacuole is active transport. This process is not passive transport because the cell is required to expend energy. In order to remove water, the contractile vacuoles collect the excess water and then contract to pump the water out of the cell. For instance, the contractile vacuoles in amoeba through diffusion and active transport collect excretory waste from the intracellular fluid.

If a paramecium’s contractile vacuole stops working, what might happen to the organism?

If a paramecium’s contractile vacuole stops working, the organism will explode or lyse from taking in too much water due to osmosis.

What does contractile vacuole mean?

Contractile vacuoles are regulatory organelles found in freshwater protozoa and lower metazoans, such as sponges and hydras. The function of the contractile vacuole is to collect excess fluid from the protoplasm and periodically empty it into the surrounding medium.

How does the contractile vacuole help maintain homeostasis?

The contractile vacuole help maintain homeostasis by preventing excessive water influx that could harm and cause rupture (lysis) to the cell. It collects excess fluids and contracts to periodically empty them into the surrounding medium, out of the organism.

Does paramecium have a contractile vacuole?

Yes, paramecium has a large contractile vacuole with an average diameter of 13 um. In a paramecium, there are two contractile vacuoles that are close to the dorsal side, one on each end of the body.

What is a contractile vacuole and how does it function?

A contractile vacuole is a specialized vacuole in eukaryotic cells such as protozoa that are involved in osmoregulation. The contractile vacuole function by allowing the flow of water from the cytoplasm of the cell and then by opening a permanent narrow neck, it discharges the water externally. In order words, a contractile vacuole is a structure that collects extra water and expels it from a protist or other organisms.

What does the contractile vacuole do in an amoeba?

The function of contractile vacuole in amoeba is to excrete cellular waste e.g ammonia and excess water by exocytosis. This is done by the contractile vacuole merging with the cell membrane to expel the waste into the environment. The contractile vacuole moves to the surface of the cell when full and undergoes exocytosis.

What does a contractile vacuole do in a paramecium?

The function of contractile vacuole in paramecium includes excretion, respiration, and osmoregulation.

Does euglena have a contractile vacuole?

Yes, the euglena has a contractile vacuole that is anterior and fixed. The function of contractile vacuole in euglena is to expel the excess water in the cell towards the reservoir.

Where is the contractile vacuole located?

The contractile vacuole is located within the cytoplasm of the cells of protists.

What is the function of contractile vacuole in euglena?

The function of contractile vacuole in euglena is to expel the excess water in the cell towards the reservoir.

Do amoeba have contractile vacuoles?

Yes, amoeba possesses one large contractile vacuole with an average diameter of 45 µm. The function of contractile vacuole in amoeba is to excrete cellular waste e.g ammonia and excess water by exocytosis.

What does a contractile vacuole look like?

When viewed with an electron microscope, the contractile vacuole structure looks like a space surrounded by a system of membranous vesicles and (or) tubules. In most cells, several structures such as membrane folds, tubules, water tracts, and small vesicles are attached to the contractile vacuole.

Why does an amoeba need a contractile vacuole?

An amoeba needs a contractile vacuole because it controls the intracellular water balance of the cell by collecting and expelling excess water out of the cell. This allows the amoeba to survive under hypotonic stress.

What cells have contractile vacuole?

It’s mostly cells that lack cell walls that have contractile vacuole. This special kind of vacuole is found in single-celled organisms without a cell wall. Contractile vacuoles can be found predominantly in the kingdom Protista e.g amoeba, paramecium, euglena, etc.

What is the function of the contractile vacuole in protozoans?

In protozoans, the function of the contractile vacuole is to control the intracellular water balance by accumulating and expelling excess water out of the cell. This allows these organisms to survive under hypotonic stress as in pond water.

Would a contractile vacuole contract more or less in saltwater?

A contractile vacuole does not contract to expel water in saltwater. This is because the solute concentration outside the cell is more than the solute concentration inside the cell. Hence, the water flows out of the cell down the concentration gradient.

Whereas, in freshwater, contractile vacuoles are needed to move water out against the concentration gradient because water comes into the cell due to osmosis. This occurs in freshwater because the solute concentration outside the cell is less than the solute concentration inside the cell.

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